1.. include:: <isonum.txt>
2
3============================================
4Reliability, Availability and Serviceability
5============================================
6
7RAS concepts
8************
9
10Reliability, Availability and Serviceability (RAS) is a concept used on
11servers meant to measure their robustness.
12
13Reliability
14  is the probability that a system will produce correct outputs.
15
16  * Generally measured as Mean Time Between Failures (MTBF)
17  * Enhanced by features that help to avoid, detect and repair hardware faults
18
19Availability
20  is the probability that a system is operational at a given time
21
22  * Generally measured as a percentage of downtime per a period of time
23  * Often uses mechanisms to detect and correct hardware faults in
24    runtime;
25
26Serviceability (or maintainability)
27  is the simplicity and speed with which a system can be repaired or
28  maintained
29
30  * Generally measured on Mean Time Between Repair (MTBR)
31
32Improving RAS
33-------------
34
35In order to reduce systems downtime, a system should be capable of detecting
36hardware errors, and, when possible correcting them in runtime. It should
37also provide mechanisms to detect hardware degradation, in order to warn
38the system administrator to take the action of replacing a component before
39it causes data loss or system downtime.
40
41Among the monitoring measures, the most usual ones include:
42
43* CPU – detect errors at instruction execution and at L1/L2/L3 caches;
44* Memory – add error correction logic (ECC) to detect and correct errors;
45* I/O – add CRC checksums for transferred data;
46* Storage – RAID, journal file systems, checksums,
47  Self-Monitoring, Analysis and Reporting Technology (SMART).
48
49By monitoring the number of occurrences of error detections, it is possible
50to identify if the probability of hardware errors is increasing, and, on such
51case, do a preventive maintenance to replace a degraded component while
52those errors are correctable.
53
54Types of errors
55---------------
56
57Most mechanisms used on modern systems use technologies like Hamming
58Codes that allow error correction when the number of errors on a bit packet
59is below a threshold. If the number of errors is above, those mechanisms
60can indicate with a high degree of confidence that an error happened, but
61they can't correct.
62
63Also, sometimes an error occur on a component that it is not used. For
64example, a part of the memory that it is not currently allocated.
65
66That defines some categories of errors:
67
68* **Correctable Error (CE)** - the error detection mechanism detected and
69  corrected the error. Such errors are usually not fatal, although some
70  Kernel mechanisms allow the system administrator to consider them as fatal.
71
72* **Uncorrected Error (UE)** - the amount of errors happened above the error
73  correction threshold, and the system was unable to auto-correct.
74
75* **Fatal Error** - when an UE error happens on a critical component of the
76  system (for example, a piece of the Kernel got corrupted by an UE), the
77  only reliable way to avoid data corruption is to hang or reboot the machine.
78
79* **Non-fatal Error** - when an UE error happens on an unused component,
80  like a CPU in power down state or an unused memory bank, the system may
81  still run, eventually replacing the affected hardware by a hot spare,
82  if available.
83
84  Also, when an error happens on a userspace process, it is also possible to
85  kill such process and let userspace restart it.
86
87The mechanism for handling non-fatal errors is usually complex and may
88require the help of some userspace application, in order to apply the
89policy desired by the system administrator.
90
91Identifying a bad hardware component
92------------------------------------
93
94Just detecting a hardware flaw is usually not enough, as the system needs
95to pinpoint to the minimal replaceable unit (MRU) that should be exchanged
96to make the hardware reliable again.
97
98So, it requires not only error logging facilities, but also mechanisms that
99will translate the error message to the silkscreen or component label for
100the MRU.
101
102Typically, it is very complex for memory, as modern CPUs interlace memory
103from different memory modules, in order to provide a better performance. The
104DMI BIOS usually have a list of memory module labels, with can be obtained
105using the ``dmidecode`` tool. For example, on a desktop machine, it shows::
106
107	Memory Device
108		Total Width: 64 bits
109		Data Width: 64 bits
110		Size: 16384 MB
111		Form Factor: SODIMM
112		Set: None
113		Locator: ChannelA-DIMM0
114		Bank Locator: BANK 0
115		Type: DDR4
116		Type Detail: Synchronous
117		Speed: 2133 MHz
118		Rank: 2
119		Configured Clock Speed: 2133 MHz
120
121On the above example, a DDR4 SO-DIMM memory module is located at the
122system's memory labeled as "BANK 0", as given by the *bank locator* field.
123Please notice that, on such system, the *total width* is equal to the
124*data width*. It means that such memory module doesn't have error
125detection/correction mechanisms.
126
127Unfortunately, not all systems use the same field to specify the memory
128bank. On this example, from an older server, ``dmidecode`` shows::
129
130	Memory Device
131		Array Handle: 0x1000
132		Error Information Handle: Not Provided
133		Total Width: 72 bits
134		Data Width: 64 bits
135		Size: 8192 MB
136		Form Factor: DIMM
137		Set: 1
138		Locator: DIMM_A1
139		Bank Locator: Not Specified
140		Type: DDR3
141		Type Detail: Synchronous Registered (Buffered)
142		Speed: 1600 MHz
143		Rank: 2
144		Configured Clock Speed: 1600 MHz
145
146There, the DDR3 RDIMM memory module is located at the system's memory labeled
147as "DIMM_A1", as given by the *locator* field. Please notice that this
148memory module has 64 bits of *data width* and 72 bits of *total width*. So,
149it has 8 extra bits to be used by error detection and correction mechanisms.
150Such kind of memory is called Error-correcting code memory (ECC memory).
151
152To make things even worse, it is not uncommon that systems with different
153labels on their system's board to use exactly the same BIOS, meaning that
154the labels provided by the BIOS won't match the real ones.
155
156ECC memory
157----------
158
159As mentioned in the previous section, ECC memory has extra bits to be
160used for error correction. In the above example, a memory module has
16164 bits of *data width*, and 72 bits of *total width*.  The extra 8
162bits which are used for the error detection and correction mechanisms
163are referred to as the *syndrome*\ [#f1]_\ [#f2]_.
164
165So, when the cpu requests the memory controller to write a word with
166*data width*, the memory controller calculates the *syndrome* in real time,
167using Hamming code, or some other error correction code, like SECDED+,
168producing a code with *total width* size. Such code is then written
169on the memory modules.
170
171At read, the *total width* bits code is converted back, using the same
172ECC code used on write, producing a word with *data width* and a *syndrome*.
173The word with *data width* is sent to the CPU, even when errors happen.
174
175The memory controller also looks at the *syndrome* in order to check if
176there was an error, and if the ECC code was able to fix such error.
177If the error was corrected, a Corrected Error (CE) happened. If not, an
178Uncorrected Error (UE) happened.
179
180The information about the CE/UE errors is stored on some special registers
181at the memory controller and can be accessed by reading such registers,
182either by BIOS, by some special CPUs or by Linux EDAC driver. On x86 64
183bit CPUs, such errors can also be retrieved via the Machine Check
184Architecture (MCA)\ [#f3]_.
185
186.. [#f1] Please notice that several memory controllers allow operation on a
187  mode called "Lock-Step", where it groups two memory modules together,
188  doing 128-bit reads/writes. That gives 16 bits for error correction, with
189  significantly improves the error correction mechanism, at the expense
190  that, when an error happens, there's no way to know what memory module is
191  to blame. So, it has to blame both memory modules.
192
193.. [#f2] Some memory controllers also allow using memory in mirror mode.
194  On such mode, the same data is written to two memory modules. At read,
195  the system checks both memory modules, in order to check if both provide
196  identical data. On such configuration, when an error happens, there's no
197  way to know what memory module is to blame. So, it has to blame both
198  memory modules (or 4 memory modules, if the system is also on Lock-step
199  mode).
200
201.. [#f3] For more details about the Machine Check Architecture (MCA),
202  please read Documentation/arch/x86/x86_64/machinecheck.rst at the Kernel tree.
203
204EDAC - Error Detection And Correction
205*************************************
206
207.. note::
208
209   "bluesmoke" was the name for this device driver subsystem when it
210   was "out-of-tree" and maintained at http://bluesmoke.sourceforge.net.
211   That site is mostly archaic now and can be used only for historical
212   purposes.
213
214   When the subsystem was pushed upstream for the first time, on
215   Kernel 2.6.16, it was renamed to ``EDAC``.
216
217Purpose
218-------
219
220The ``edac`` kernel module's goal is to detect and report hardware errors
221that occur within the computer system running under linux.
222
223Memory
224------
225
226Memory Correctable Errors (CE) and Uncorrectable Errors (UE) are the
227primary errors being harvested. These types of errors are harvested by
228the ``edac_mc`` device.
229
230Detecting CE events, then harvesting those events and reporting them,
231**can** but must not necessarily be a predictor of future UE events. With
232CE events only, the system can and will continue to operate as no data
233has been damaged yet.
234
235However, preventive maintenance and proactive part replacement of memory
236modules exhibiting CEs can reduce the likelihood of the dreaded UE events
237and system panics.
238
239Other hardware elements
240-----------------------
241
242A new feature for EDAC, the ``edac_device`` class of device, was added in
243the 2.6.23 version of the kernel.
244
245This new device type allows for non-memory type of ECC hardware detectors
246to have their states harvested and presented to userspace via the sysfs
247interface.
248
249Some architectures have ECC detectors for L1, L2 and L3 caches,
250along with DMA engines, fabric switches, main data path switches,
251interconnections, and various other hardware data paths. If the hardware
252reports it, then a edac_device device probably can be constructed to
253harvest and present that to userspace.
254
255
256PCI bus scanning
257----------------
258
259In addition, PCI devices are scanned for PCI Bus Parity and SERR Errors
260in order to determine if errors are occurring during data transfers.
261
262The presence of PCI Parity errors must be examined with a grain of salt.
263There are several add-in adapters that do **not** follow the PCI specification
264with regards to Parity generation and reporting. The specification says
265the vendor should tie the parity status bits to 0 if they do not intend
266to generate parity.  Some vendors do not do this, and thus the parity bit
267can "float" giving false positives.
268
269There is a PCI device attribute located in sysfs that is checked by
270the EDAC PCI scanning code. If that attribute is set, PCI parity/error
271scanning is skipped for that device. The attribute is::
272
273	broken_parity_status
274
275and is located in ``/sys/devices/pci<XXX>/0000:XX:YY.Z`` directories for
276PCI devices.
277
278
279Versioning
280----------
281
282EDAC is composed of a "core" module (``edac_core.ko``) and several Memory
283Controller (MC) driver modules. On a given system, the CORE is loaded
284and one MC driver will be loaded. Both the CORE and the MC driver (or
285``edac_device`` driver) have individual versions that reflect current
286release level of their respective modules.
287
288Thus, to "report" on what version a system is running, one must report
289both the CORE's and the MC driver's versions.
290
291
292Loading
293-------
294
295If ``edac`` was statically linked with the kernel then no loading
296is necessary. If ``edac`` was built as modules then simply modprobe
297the ``edac`` pieces that you need. You should be able to modprobe
298hardware-specific modules and have the dependencies load the necessary
299core modules.
300
301Example::
302
303	$ modprobe amd76x_edac
304
305loads both the ``amd76x_edac.ko`` memory controller module and the
306``edac_mc.ko`` core module.
307
308
309Sysfs interface
310---------------
311
312EDAC presents a ``sysfs`` interface for control and reporting purposes. It
313lives in the /sys/devices/system/edac directory.
314
315Within this directory there currently reside 2 components:
316
317	======= ==============================
318	mc	memory controller(s) system
319	pci	PCI control and status system
320	======= ==============================
321
322
323
324Memory Controller (mc) Model
325----------------------------
326
327Each ``mc`` device controls a set of memory modules [#f4]_. These modules
328are laid out in a Chip-Select Row (``csrowX``) and Channel table (``chX``).
329There can be multiple csrows and multiple channels.
330
331.. [#f4] Nowadays, the term DIMM (Dual In-line Memory Module) is widely
332  used to refer to a memory module, although there are other memory
333  packaging alternatives, like SO-DIMM, SIMM, etc. The UEFI
334  specification (Version 2.7) defines a memory module in the Common
335  Platform Error Record (CPER) section to be an SMBIOS Memory Device
336  (Type 17). Along this document, and inside the EDAC subsystem, the term
337  "dimm" is used for all memory modules, even when they use a
338  different kind of packaging.
339
340Memory controllers allow for several csrows, with 8 csrows being a
341typical value. Yet, the actual number of csrows depends on the layout of
342a given motherboard, memory controller and memory module characteristics.
343
344Dual channels allow for dual data length (e. g. 128 bits, on 64 bit systems)
345data transfers to/from the CPU from/to memory. Some newer chipsets allow
346for more than 2 channels, like Fully Buffered DIMMs (FB-DIMMs) memory
347controllers. The following example will assume 2 channels:
348
349	+------------+-----------------------+
350	| CS Rows    |       Channels        |
351	+------------+-----------+-----------+
352	|            |  ``ch0``  |  ``ch1``  |
353	+============+===========+===========+
354	|            |**DIMM_A0**|**DIMM_B0**|
355	+------------+-----------+-----------+
356	| ``csrow0`` |   rank0   |   rank0   |
357	+------------+-----------+-----------+
358	| ``csrow1`` |   rank1   |   rank1   |
359	+------------+-----------+-----------+
360	|            |**DIMM_A1**|**DIMM_B1**|
361	+------------+-----------+-----------+
362	| ``csrow2`` |    rank0  |  rank0    |
363	+------------+-----------+-----------+
364	| ``csrow3`` |    rank1  |  rank1    |
365	+------------+-----------+-----------+
366
367In the above example, there are 4 physical slots on the motherboard
368for memory DIMMs:
369
370	+---------+---------+
371	| DIMM_A0 | DIMM_B0 |
372	+---------+---------+
373	| DIMM_A1 | DIMM_B1 |
374	+---------+---------+
375
376Labels for these slots are usually silk-screened on the motherboard.
377Slots labeled ``A`` are channel 0 in this example. Slots labeled ``B`` are
378channel 1. Notice that there are two csrows possible on a physical DIMM.
379These csrows are allocated their csrow assignment based on the slot into
380which the memory DIMM is placed. Thus, when 1 DIMM is placed in each
381Channel, the csrows cross both DIMMs.
382
383Memory DIMMs come single or dual "ranked". A rank is a populated csrow.
384In the example above 2 dual ranked DIMMs are similarly placed. Thus,
385both csrow0 and csrow1 are populated. On the other hand, when 2 single
386ranked DIMMs are placed in slots DIMM_A0 and DIMM_B0, then they will
387have just one csrow (csrow0) and csrow1 will be empty. The pattern
388repeats itself for csrow2 and csrow3. Also note that some memory
389controllers don't have any logic to identify the memory module, see
390``rankX`` directories below.
391
392The representation of the above is reflected in the directory
393tree in EDAC's sysfs interface. Starting in directory
394``/sys/devices/system/edac/mc``, each memory controller will be
395represented by its own ``mcX`` directory, where ``X`` is the
396index of the MC::
397
398	..../edac/mc/
399		   |
400		   |->mc0
401		   |->mc1
402		   |->mc2
403		   ....
404
405Under each ``mcX`` directory each ``csrowX`` is again represented by a
406``csrowX``, where ``X`` is the csrow index::
407
408	.../mc/mc0/
409		|
410		|->csrow0
411		|->csrow2
412		|->csrow3
413		....
414
415Notice that there is no csrow1, which indicates that csrow0 is composed
416of a single ranked DIMMs. This should also apply in both Channels, in
417order to have dual-channel mode be operational. Since both csrow2 and
418csrow3 are populated, this indicates a dual ranked set of DIMMs for
419channels 0 and 1.
420
421Within each of the ``mcX`` and ``csrowX`` directories are several EDAC
422control and attribute files.
423
424``mcX`` directories
425-------------------
426
427In ``mcX`` directories are EDAC control and attribute files for
428this ``X`` instance of the memory controllers.
429
430For a description of the sysfs API, please see:
431
432	Documentation/ABI/testing/sysfs-devices-edac
433
434
435``dimmX`` or ``rankX`` directories
436----------------------------------
437
438The recommended way to use the EDAC subsystem is to look at the information
439provided by the ``dimmX`` or ``rankX`` directories [#f5]_.
440
441A typical EDAC system has the following structure under
442``/sys/devices/system/edac/``\ [#f6]_::
443
444	/sys/devices/system/edac/
445	├── mc
446	│   ├── mc0
447	│   │   ├── ce_count
448	│   │   ├── ce_noinfo_count
449	│   │   ├── dimm0
450	│   │   │   ├── dimm_ce_count
451	│   │   │   ├── dimm_dev_type
452	│   │   │   ├── dimm_edac_mode
453	│   │   │   ├── dimm_label
454	│   │   │   ├── dimm_location
455	│   │   │   ├── dimm_mem_type
456	│   │   │   ├── dimm_ue_count
457	│   │   │   ├── size
458	│   │   │   └── uevent
459	│   │   ├── max_location
460	│   │   ├── mc_name
461	│   │   ├── reset_counters
462	│   │   ├── seconds_since_reset
463	│   │   ├── size_mb
464	│   │   ├── ue_count
465	│   │   ├── ue_noinfo_count
466	│   │   └── uevent
467	│   ├── mc1
468	│   │   ├── ce_count
469	│   │   ├── ce_noinfo_count
470	│   │   ├── dimm0
471	│   │   │   ├── dimm_ce_count
472	│   │   │   ├── dimm_dev_type
473	│   │   │   ├── dimm_edac_mode
474	│   │   │   ├── dimm_label
475	│   │   │   ├── dimm_location
476	│   │   │   ├── dimm_mem_type
477	│   │   │   ├── dimm_ue_count
478	│   │   │   ├── size
479	│   │   │   └── uevent
480	│   │   ├── max_location
481	│   │   ├── mc_name
482	│   │   ├── reset_counters
483	│   │   ├── seconds_since_reset
484	│   │   ├── size_mb
485	│   │   ├── ue_count
486	│   │   ├── ue_noinfo_count
487	│   │   └── uevent
488	│   └── uevent
489	└── uevent
490
491In the ``dimmX`` directories are EDAC control and attribute files for
492this ``X`` memory module:
493
494- ``size`` - Total memory managed by this csrow attribute file
495
496	This attribute file displays, in count of megabytes, the memory
497	that this csrow contains.
498
499- ``dimm_ue_count`` - Uncorrectable Errors count attribute file
500
501	This attribute file displays the total count of uncorrectable
502	errors that have occurred on this DIMM. If panic_on_ue is set
503	this counter will not have a chance to increment, since EDAC
504	will panic the system.
505
506- ``dimm_ce_count`` - Correctable Errors count attribute file
507
508	This attribute file displays the total count of correctable
509	errors that have occurred on this DIMM. This count is very
510	important to examine. CEs provide early indications that a
511	DIMM is beginning to fail. This count field should be
512	monitored for non-zero values and report such information
513	to the system administrator.
514
515- ``dimm_dev_type``  - Device type attribute file
516
517	This attribute file will display what type of DRAM device is
518	being utilized on this DIMM.
519	Examples:
520
521		- x1
522		- x2
523		- x4
524		- x8
525
526- ``dimm_edac_mode`` - EDAC Mode of operation attribute file
527
528	This attribute file will display what type of Error detection
529	and correction is being utilized.
530
531- ``dimm_label`` - memory module label control file
532
533	This control file allows this DIMM to have a label assigned
534	to it. With this label in the module, when errors occur
535	the output can provide the DIMM label in the system log.
536	This becomes vital for panic events to isolate the
537	cause of the UE event.
538
539	DIMM Labels must be assigned after booting, with information
540	that correctly identifies the physical slot with its
541	silk screen label. This information is currently very
542	motherboard specific and determination of this information
543	must occur in userland at this time.
544
545- ``dimm_location`` - location of the memory module
546
547	The location can have up to 3 levels, and describe how the
548	memory controller identifies the location of a memory module.
549	Depending on the type of memory and memory controller, it
550	can be:
551
552		- *csrow* and *channel* - used when the memory controller
553		  doesn't identify a single DIMM - e. g. in ``rankX`` dir;
554		- *branch*, *channel*, *slot* - typically used on FB-DIMM memory
555		  controllers;
556		- *channel*, *slot* - used on Nehalem and newer Intel drivers.
557
558- ``dimm_mem_type`` - Memory Type attribute file
559
560	This attribute file will display what type of memory is currently
561	on this csrow. Normally, either buffered or unbuffered memory.
562	Examples:
563
564		- Registered-DDR
565		- Unbuffered-DDR
566
567.. [#f5] On some systems, the memory controller doesn't have any logic
568  to identify the memory module. On such systems, the directory is called ``rankX`` and works on a similar way as the ``csrowX`` directories.
569  On modern Intel memory controllers, the memory controller identifies the
570  memory modules directly. On such systems, the directory is called ``dimmX``.
571
572.. [#f6] There are also some ``power`` directories and ``subsystem``
573  symlinks inside the sysfs mapping that are automatically created by
574  the sysfs subsystem. Currently, they serve no purpose.
575
576``csrowX`` directories
577----------------------
578
579When CONFIG_EDAC_LEGACY_SYSFS is enabled, sysfs will contain the ``csrowX``
580directories. As this API doesn't work properly for Rambus, FB-DIMMs and
581modern Intel Memory Controllers, this is being deprecated in favor of
582``dimmX`` directories.
583
584In the ``csrowX`` directories are EDAC control and attribute files for
585this ``X`` instance of csrow:
586
587
588- ``ue_count`` - Total Uncorrectable Errors count attribute file
589
590	This attribute file displays the total count of uncorrectable
591	errors that have occurred on this csrow. If panic_on_ue is set
592	this counter will not have a chance to increment, since EDAC
593	will panic the system.
594
595
596- ``ce_count`` - Total Correctable Errors count attribute file
597
598	This attribute file displays the total count of correctable
599	errors that have occurred on this csrow. This count is very
600	important to examine. CEs provide early indications that a
601	DIMM is beginning to fail. This count field should be
602	monitored for non-zero values and report such information
603	to the system administrator.
604
605
606- ``size_mb`` - Total memory managed by this csrow attribute file
607
608	This attribute file displays, in count of megabytes, the memory
609	that this csrow contains.
610
611
612- ``mem_type`` - Memory Type attribute file
613
614	This attribute file will display what type of memory is currently
615	on this csrow. Normally, either buffered or unbuffered memory.
616	Examples:
617
618		- Registered-DDR
619		- Unbuffered-DDR
620
621
622- ``edac_mode`` - EDAC Mode of operation attribute file
623
624	This attribute file will display what type of Error detection
625	and correction is being utilized.
626
627
628- ``dev_type`` - Device type attribute file
629
630	This attribute file will display what type of DRAM device is
631	being utilized on this DIMM.
632	Examples:
633
634		- x1
635		- x2
636		- x4
637		- x8
638
639
640- ``ch0_ce_count`` - Channel 0 CE Count attribute file
641
642	This attribute file will display the count of CEs on this
643	DIMM located in channel 0.
644
645
646- ``ch0_ue_count`` - Channel 0 UE Count attribute file
647
648	This attribute file will display the count of UEs on this
649	DIMM located in channel 0.
650
651
652- ``ch0_dimm_label`` - Channel 0 DIMM Label control file
653
654
655	This control file allows this DIMM to have a label assigned
656	to it. With this label in the module, when errors occur
657	the output can provide the DIMM label in the system log.
658	This becomes vital for panic events to isolate the
659	cause of the UE event.
660
661	DIMM Labels must be assigned after booting, with information
662	that correctly identifies the physical slot with its
663	silk screen label. This information is currently very
664	motherboard specific and determination of this information
665	must occur in userland at this time.
666
667
668- ``ch1_ce_count`` - Channel 1 CE Count attribute file
669
670
671	This attribute file will display the count of CEs on this
672	DIMM located in channel 1.
673
674
675- ``ch1_ue_count`` - Channel 1 UE Count attribute file
676
677
678	This attribute file will display the count of UEs on this
679	DIMM located in channel 0.
680
681
682- ``ch1_dimm_label`` - Channel 1 DIMM Label control file
683
684	This control file allows this DIMM to have a label assigned
685	to it. With this label in the module, when errors occur
686	the output can provide the DIMM label in the system log.
687	This becomes vital for panic events to isolate the
688	cause of the UE event.
689
690	DIMM Labels must be assigned after booting, with information
691	that correctly identifies the physical slot with its
692	silk screen label. This information is currently very
693	motherboard specific and determination of this information
694	must occur in userland at this time.
695
696
697System Logging
698--------------
699
700If logging for UEs and CEs is enabled, then system logs will contain
701information indicating that errors have been detected::
702
703  EDAC MC0: CE page 0x283, offset 0xce0, grain 8, syndrome 0x6ec3, row 0, channel 1 "DIMM_B1": amd76x_edac
704  EDAC MC0: CE page 0x1e5, offset 0xfb0, grain 8, syndrome 0xb741, row 0, channel 1 "DIMM_B1": amd76x_edac
705
706
707The structure of the message is:
708
709	+---------------------------------------+-------------+
710	| Content                               | Example     |
711	+=======================================+=============+
712	| The memory controller                 | MC0         |
713	+---------------------------------------+-------------+
714	| Error type                            | CE          |
715	+---------------------------------------+-------------+
716	| Memory page                           | 0x283       |
717	+---------------------------------------+-------------+
718	| Offset in the page                    | 0xce0       |
719	+---------------------------------------+-------------+
720	| The byte granularity                  | grain 8     |
721	| or resolution of the error            |             |
722	+---------------------------------------+-------------+
723	| The error syndrome                    | 0xb741      |
724	+---------------------------------------+-------------+
725	| Memory row                            | row 0       |
726	+---------------------------------------+-------------+
727	| Memory channel                        | channel 1   |
728	+---------------------------------------+-------------+
729	| DIMM label, if set prior              | DIMM B1     |
730	+---------------------------------------+-------------+
731	| And then an optional, driver-specific |             |
732	| message that may have additional      |             |
733	| information.                          |             |
734	+---------------------------------------+-------------+
735
736Both UEs and CEs with no info will lack all but memory controller, error
737type, a notice of "no info" and then an optional, driver-specific error
738message.
739
740
741PCI Bus Parity Detection
742------------------------
743
744On Header Type 00 devices, the primary status is looked at for any
745parity error regardless of whether parity is enabled on the device or
746not. (The spec indicates parity is generated in some cases). On Header
747Type 01 bridges, the secondary status register is also looked at to see
748if parity occurred on the bus on the other side of the bridge.
749
750
751Sysfs configuration
752-------------------
753
754Under ``/sys/devices/system/edac/pci`` are control and attribute files as
755follows:
756
757
758- ``check_pci_parity`` - Enable/Disable PCI Parity checking control file
759
760	This control file enables or disables the PCI Bus Parity scanning
761	operation. Writing a 1 to this file enables the scanning. Writing
762	a 0 to this file disables the scanning.
763
764	Enable::
765
766		echo "1" >/sys/devices/system/edac/pci/check_pci_parity
767
768	Disable::
769
770		echo "0" >/sys/devices/system/edac/pci/check_pci_parity
771
772
773- ``pci_parity_count`` - Parity Count
774
775	This attribute file will display the number of parity errors that
776	have been detected.
777
778
779Module parameters
780-----------------
781
782- ``edac_mc_panic_on_ue`` - Panic on UE control file
783
784	An uncorrectable error will cause a machine panic.  This is usually
785	desirable.  It is a bad idea to continue when an uncorrectable error
786	occurs - it is indeterminate what was uncorrected and the operating
787	system context might be so mangled that continuing will lead to further
788	corruption. If the kernel has MCE configured, then EDAC will never
789	notice the UE.
790
791	LOAD TIME::
792
793		module/kernel parameter: edac_mc_panic_on_ue=[0|1]
794
795	RUN TIME::
796
797		echo "1" > /sys/module/edac_core/parameters/edac_mc_panic_on_ue
798
799
800- ``edac_mc_log_ue`` - Log UE control file
801
802
803	Generate kernel messages describing uncorrectable errors.  These errors
804	are reported through the system message log system.  UE statistics
805	will be accumulated even when UE logging is disabled.
806
807	LOAD TIME::
808
809		module/kernel parameter: edac_mc_log_ue=[0|1]
810
811	RUN TIME::
812
813		echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ue
814
815
816- ``edac_mc_log_ce`` - Log CE control file
817
818
819	Generate kernel messages describing correctable errors.  These
820	errors are reported through the system message log system.
821	CE statistics will be accumulated even when CE logging is disabled.
822
823	LOAD TIME::
824
825		module/kernel parameter: edac_mc_log_ce=[0|1]
826
827	RUN TIME::
828
829		echo "1" > /sys/module/edac_core/parameters/edac_mc_log_ce
830
831
832- ``edac_mc_poll_msec`` - Polling period control file
833
834
835	The time period, in milliseconds, for polling for error information.
836	Too small a value wastes resources.  Too large a value might delay
837	necessary handling of errors and might loose valuable information for
838	locating the error.  1000 milliseconds (once each second) is the current
839	default. Systems which require all the bandwidth they can get, may
840	increase this.
841
842	LOAD TIME::
843
844		module/kernel parameter: edac_mc_poll_msec=[0|1]
845
846	RUN TIME::
847
848		echo "1000" > /sys/module/edac_core/parameters/edac_mc_poll_msec
849
850
851- ``panic_on_pci_parity`` - Panic on PCI PARITY Error
852
853
854	This control file enables or disables panicking when a parity
855	error has been detected.
856
857
858	module/kernel parameter::
859
860			edac_panic_on_pci_pe=[0|1]
861
862	Enable::
863
864		echo "1" > /sys/module/edac_core/parameters/edac_panic_on_pci_pe
865
866	Disable::
867
868		echo "0" > /sys/module/edac_core/parameters/edac_panic_on_pci_pe
869
870
871
872EDAC device type
873----------------
874
875In the header file, edac_pci.h, there is a series of edac_device structures
876and APIs for the EDAC_DEVICE.
877
878User space access to an edac_device is through the sysfs interface.
879
880At the location ``/sys/devices/system/edac`` (sysfs) new edac_device devices
881will appear.
882
883There is a three level tree beneath the above ``edac`` directory. For example,
884the ``test_device_edac`` device (found at the http://bluesmoke.sourceforget.net
885website) installs itself as::
886
887	/sys/devices/system/edac/test-instance
888
889in this directory are various controls, a symlink and one or more ``instance``
890directories.
891
892The standard default controls are:
893
894	==============	=======================================================
895	log_ce		boolean to log CE events
896	log_ue		boolean to log UE events
897	panic_on_ue	boolean to ``panic`` the system if an UE is encountered
898			(default off, can be set true via startup script)
899	poll_msec	time period between POLL cycles for events
900	==============	=======================================================
901
902The test_device_edac device adds at least one of its own custom control:
903
904	==============	==================================================
905	test_bits	which in the current test driver does nothing but
906			show how it is installed. A ported driver can
907			add one or more such controls and/or attributes
908			for specific uses.
909			One out-of-tree driver uses controls here to allow
910			for ERROR INJECTION operations to hardware
911			injection registers
912	==============	==================================================
913
914The symlink points to the 'struct dev' that is registered for this edac_device.
915
916Instances
917---------
918
919One or more instance directories are present. For the ``test_device_edac``
920case:
921
922	+----------------+
923	| test-instance0 |
924	+----------------+
925
926
927In this directory there are two default counter attributes, which are totals of
928counter in deeper subdirectories.
929
930	==============	====================================
931	ce_count	total of CE events of subdirectories
932	ue_count	total of UE events of subdirectories
933	==============	====================================
934
935Blocks
936------
937
938At the lowest directory level is the ``block`` directory. There can be 0, 1
939or more blocks specified in each instance:
940
941	+-------------+
942	| test-block0 |
943	+-------------+
944
945In this directory the default attributes are:
946
947	==============	================================================
948	ce_count	which is counter of CE events for this ``block``
949			of hardware being monitored
950	ue_count	which is counter of UE events for this ``block``
951			of hardware being monitored
952	==============	================================================
953
954
955The ``test_device_edac`` device adds 4 attributes and 1 control:
956
957	================== ====================================================
958	test-block-bits-0	for every POLL cycle this counter
959				is incremented
960	test-block-bits-1	every 10 cycles, this counter is bumped once,
961				and test-block-bits-0 is set to 0
962	test-block-bits-2	every 100 cycles, this counter is bumped once,
963				and test-block-bits-1 is set to 0
964	test-block-bits-3	every 1000 cycles, this counter is bumped once,
965				and test-block-bits-2 is set to 0
966	================== ====================================================
967
968
969	================== ====================================================
970	reset-counters		writing ANY thing to this control will
971				reset all the above counters.
972	================== ====================================================
973
974
975Use of the ``test_device_edac`` driver should enable any others to create their own
976unique drivers for their hardware systems.
977
978The ``test_device_edac`` sample driver is located at the
979http://bluesmoke.sourceforge.net project site for EDAC.
980
981
982Usage of EDAC APIs on Nehalem and newer Intel CPUs
983--------------------------------------------------
984
985On older Intel architectures, the memory controller was part of the North
986Bridge chipset. Nehalem, Sandy Bridge, Ivy Bridge, Haswell, Sky Lake and
987newer Intel architectures integrated an enhanced version of the memory
988controller (MC) inside the CPUs.
989
990This chapter will cover the differences of the enhanced memory controllers
991found on newer Intel CPUs, such as ``i7core_edac``, ``sb_edac`` and
992``sbx_edac`` drivers.
993
994.. note::
995
996   The Xeon E7 processor families use a separate chip for the memory
997   controller, called Intel Scalable Memory Buffer. This section doesn't
998   apply for such families.
999
10001) There is one Memory Controller per Quick Patch Interconnect
1001   (QPI). At the driver, the term "socket" means one QPI. This is
1002   associated with a physical CPU socket.
1003
1004   Each MC have 3 physical read channels, 3 physical write channels and
1005   3 logic channels. The driver currently sees it as just 3 channels.
1006   Each channel can have up to 3 DIMMs.
1007
1008   The minimum known unity is DIMMs. There are no information about csrows.
1009   As EDAC API maps the minimum unity is csrows, the driver sequentially
1010   maps channel/DIMM into different csrows.
1011
1012   For example, supposing the following layout::
1013
1014	Ch0 phy rd0, wr0 (0x063f4031): 2 ranks, UDIMMs
1015	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
1016	  dimm 1 1024 Mb offset: 4, bank: 8, rank: 1, row: 0x4000, col: 0x400
1017        Ch1 phy rd1, wr1 (0x063f4031): 2 ranks, UDIMMs
1018	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
1019	Ch2 phy rd3, wr3 (0x063f4031): 2 ranks, UDIMMs
1020	  dimm 0 1024 Mb offset: 0, bank: 8, rank: 1, row: 0x4000, col: 0x400
1021
1022   The driver will map it as::
1023
1024	csrow0: channel 0, dimm0
1025	csrow1: channel 0, dimm1
1026	csrow2: channel 1, dimm0
1027	csrow3: channel 2, dimm0
1028
1029   exports one DIMM per csrow.
1030
1031   Each QPI is exported as a different memory controller.
1032
10332) The MC has the ability to inject errors to test drivers. The drivers
1034   implement this functionality via some error injection nodes:
1035
1036   For injecting a memory error, there are some sysfs nodes, under
1037   ``/sys/devices/system/edac/mc/mc?/``:
1038
1039   - ``inject_addrmatch/*``:
1040      Controls the error injection mask register. It is possible to specify
1041      several characteristics of the address to match an error code::
1042
1043         dimm = the affected dimm. Numbers are relative to a channel;
1044         rank = the memory rank;
1045         channel = the channel that will generate an error;
1046         bank = the affected bank;
1047         page = the page address;
1048         column (or col) = the address column.
1049
1050      each of the above values can be set to "any" to match any valid value.
1051
1052      At driver init, all values are set to any.
1053
1054      For example, to generate an error at rank 1 of dimm 2, for any channel,
1055      any bank, any page, any column::
1056
1057		echo 2 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/dimm
1058		echo 1 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/rank
1059
1060	To return to the default behaviour of matching any, you can do::
1061
1062		echo any >/sys/devices/system/edac/mc/mc0/inject_addrmatch/dimm
1063		echo any >/sys/devices/system/edac/mc/mc0/inject_addrmatch/rank
1064
1065   - ``inject_eccmask``:
1066          specifies what bits will have troubles,
1067
1068   - ``inject_section``:
1069       specifies what ECC cache section will get the error::
1070
1071		3 for both
1072		2 for the highest
1073		1 for the lowest
1074
1075   - ``inject_type``:
1076       specifies the type of error, being a combination of the following bits::
1077
1078		bit 0 - repeat
1079		bit 1 - ecc
1080		bit 2 - parity
1081
1082   - ``inject_enable``:
1083       starts the error generation when something different than 0 is written.
1084
1085   All inject vars can be read. root permission is needed for write.
1086
1087   Datasheet states that the error will only be generated after a write on an
1088   address that matches inject_addrmatch. It seems, however, that reading will
1089   also produce an error.
1090
1091   For example, the following code will generate an error for any write access
1092   at socket 0, on any DIMM/address on channel 2::
1093
1094	echo 2 >/sys/devices/system/edac/mc/mc0/inject_addrmatch/channel
1095	echo 2 >/sys/devices/system/edac/mc/mc0/inject_type
1096	echo 64 >/sys/devices/system/edac/mc/mc0/inject_eccmask
1097	echo 3 >/sys/devices/system/edac/mc/mc0/inject_section
1098	echo 1 >/sys/devices/system/edac/mc/mc0/inject_enable
1099	dd if=/dev/mem of=/dev/null seek=16k bs=4k count=1 >& /dev/null
1100
1101   For socket 1, it is needed to replace "mc0" by "mc1" at the above
1102   commands.
1103
1104   The generated error message will look like::
1105
1106	EDAC MC0: UE row 0, channel-a= 0 channel-b= 0 labels "-": NON_FATAL (addr = 0x0075b980, socket=0, Dimm=0, Channel=2, syndrome=0x00000040, count=1, Err=8c0000400001009f:4000080482 (read error: read ECC error))
1107
11083) Corrected Error memory register counters
1109
1110   Those newer MCs have some registers to count memory errors. The driver
1111   uses those registers to report Corrected Errors on devices with Registered
1112   DIMMs.
1113
1114   However, those counters don't work with Unregistered DIMM. As the chipset
1115   offers some counters that also work with UDIMMs (but with a worse level of
1116   granularity than the default ones), the driver exposes those registers for
1117   UDIMM memories.
1118
1119   They can be read by looking at the contents of ``all_channel_counts/``::
1120
1121     $ for i in /sys/devices/system/edac/mc/mc0/all_channel_counts/*; do echo $i; cat $i; done
1122	/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm0
1123	0
1124	/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm1
1125	0
1126	/sys/devices/system/edac/mc/mc0/all_channel_counts/udimm2
1127	0
1128
1129   What happens here is that errors on different csrows, but at the same
1130   dimm number will increment the same counter.
1131   So, in this memory mapping::
1132
1133	csrow0: channel 0, dimm0
1134	csrow1: channel 0, dimm1
1135	csrow2: channel 1, dimm0
1136	csrow3: channel 2, dimm0
1137
1138   The hardware will increment udimm0 for an error at the first dimm at either
1139   csrow0, csrow2  or csrow3;
1140
1141   The hardware will increment udimm1 for an error at the second dimm at either
1142   csrow0, csrow2  or csrow3;
1143
1144   The hardware will increment udimm2 for an error at the third dimm at either
1145   csrow0, csrow2  or csrow3;
1146
11474) Standard error counters
1148
1149   The standard error counters are generated when an mcelog error is received
1150   by the driver. Since, with UDIMM, this is counted by software, it is
1151   possible that some errors could be lost. With RDIMM's, they display the
1152   contents of the registers
1153
1154Reference documents used on ``amd64_edac``
1155------------------------------------------
1156
1157``amd64_edac`` module is based on the following documents
1158(available from http://support.amd.com/en-us/search/tech-docs):
1159
11601. :Title:  BIOS and Kernel Developer's Guide for AMD Athlon 64 and AMD
1161	   Opteron Processors
1162   :AMD publication #: 26094
1163   :Revision: 3.26
1164   :Link: http://support.amd.com/TechDocs/26094.PDF
1165
11662. :Title:  BIOS and Kernel Developer's Guide for AMD NPT Family 0Fh
1167	   Processors
1168   :AMD publication #: 32559
1169   :Revision: 3.00
1170   :Issue Date: May 2006
1171   :Link: http://support.amd.com/TechDocs/32559.pdf
1172
11733. :Title:  BIOS and Kernel Developer's Guide (BKDG) For AMD Family 10h
1174	   Processors
1175   :AMD publication #: 31116
1176   :Revision: 3.00
1177   :Issue Date: September 07, 2007
1178   :Link: http://support.amd.com/TechDocs/31116.pdf
1179
11804. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 15h
1181	  Models 30h-3Fh Processors
1182   :AMD publication #: 49125
1183   :Revision: 3.06
1184   :Issue Date: 2/12/2015 (latest release)
1185   :Link: http://support.amd.com/TechDocs/49125_15h_Models_30h-3Fh_BKDG.pdf
1186
11875. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 15h
1188	  Models 60h-6Fh Processors
1189   :AMD publication #: 50742
1190   :Revision: 3.01
1191   :Issue Date: 7/23/2015 (latest release)
1192   :Link: http://support.amd.com/TechDocs/50742_15h_Models_60h-6Fh_BKDG.pdf
1193
11946. :Title: BIOS and Kernel Developer's Guide (BKDG) for AMD Family 16h
1195	  Models 00h-0Fh Processors
1196   :AMD publication #: 48751
1197   :Revision: 3.03
1198   :Issue Date: 2/23/2015 (latest release)
1199   :Link: http://support.amd.com/TechDocs/48751_16h_bkdg.pdf
1200
1201Credits
1202=======
1203
1204* Written by Doug Thompson <dougthompson@xmission.com>
1205
1206  - 7 Dec 2005
1207  - 17 Jul 2007	Updated
1208
1209* |copy| Mauro Carvalho Chehab
1210
1211  - 05 Aug 2009	Nehalem interface
1212  - 26 Oct 2016 Converted to ReST and cleanups at the Nehalem section
1213
1214* EDAC authors/maintainers:
1215
1216  - Doug Thompson, Dave Jiang, Dave Peterson et al,
1217  - Mauro Carvalho Chehab
1218  - Borislav Petkov
1219  - original author: Thayne Harbaugh
1220