1perf-c2c(1)
2===========
3
4NAME
5----
6perf-c2c - Shared Data C2C/HITM Analyzer.
7
8SYNOPSIS
9--------
10[verse]
11'perf c2c record' [<options>] <command>
12'perf c2c record' [<options>] -- [<record command options>] <command>
13'perf c2c report' [<options>]
14
15DESCRIPTION
16-----------
17C2C stands for Cache To Cache.
18
19The perf c2c tool provides means for Shared Data C2C/HITM analysis. It allows
20you to track down the cacheline contentions.
21
22On x86, the tool is based on load latency and precise store facility events
23provided by Intel CPUs. On PowerPC, the tool uses random instruction sampling
24with thresholding feature.
25
26These events provide:
27  - memory address of the access
28  - type of the access (load and store details)
29  - latency (in cycles) of the load access
30
31The c2c tool provide means to record this data and report back access details
32for cachelines with highest contention - highest number of HITM accesses.
33
34The basic workflow with this tool follows the standard record/report phase.
35User uses the record command to record events data and report command to
36display it.
37
38
39RECORD OPTIONS
40--------------
41-e::
42--event=::
43	Select the PMU event. Use 'perf c2c record -e list'
44	to list available events.
45
46-v::
47--verbose::
48	Be more verbose (show counter open errors, etc).
49
50-l::
51--ldlat::
52	Configure mem-loads latency. (x86 only)
53
54-k::
55--all-kernel::
56	Configure all used events to run in kernel space.
57
58-u::
59--all-user::
60	Configure all used events to run in user space.
61
62REPORT OPTIONS
63--------------
64-k::
65--vmlinux=<file>::
66	vmlinux pathname
67
68-v::
69--verbose::
70	Be more verbose (show counter open errors, etc).
71
72-i::
73--input::
74	Specify the input file to process.
75
76-N::
77--node-info::
78	Show extra node info in report (see NODE INFO section)
79
80-c::
81--coalesce::
82	Specify sorting fields for single cacheline display.
83	Following fields are available: tid,pid,iaddr,dso
84	(see COALESCE)
85
86-g::
87--call-graph::
88	Setup callchains parameters.
89	Please refer to perf-report man page for details.
90
91--stdio::
92	Force the stdio output (see STDIO OUTPUT)
93
94--stats::
95	Display only statistic tables and force stdio mode.
96
97--full-symbols::
98	Display full length of symbols.
99
100--no-source::
101	Do not display Source:Line column.
102
103--show-all::
104	Show all captured HITM lines, with no regard to HITM % 0.0005 limit.
105
106-f::
107--force::
108	Don't do ownership validation.
109
110-d::
111--display::
112	Switch to HITM type (rmt, lcl) to display and sort on. Total HITMs as default.
113
114--stitch-lbr::
115	Show callgraph with stitched LBRs, which may have more complete
116	callgraph. The perf.data file must have been obtained using
117	perf c2c record --call-graph lbr.
118	Disabled by default. In common cases with call stack overflows,
119	it can recreate better call stacks than the default lbr call stack
120	output. But this approach is not full proof. There can be cases
121	where it creates incorrect call stacks from incorrect matches.
122	The known limitations include exception handing such as
123	setjmp/longjmp will have calls/returns not match.
124
125C2C RECORD
126----------
127The perf c2c record command setup options related to HITM cacheline analysis
128and calls standard perf record command.
129
130Following perf record options are configured by default:
131(check perf record man page for details)
132
133  -W,-d,--phys-data,--sample-cpu
134
135Unless specified otherwise with '-e' option, following events are monitored by
136default on x86:
137
138  cpu/mem-loads,ldlat=30/P
139  cpu/mem-stores/P
140
141and following on PowerPC:
142
143  cpu/mem-loads/
144  cpu/mem-stores/
145
146User can pass any 'perf record' option behind '--' mark, like (to enable
147callchains and system wide monitoring):
148
149  $ perf c2c record -- -g -a
150
151Please check RECORD OPTIONS section for specific c2c record options.
152
153C2C REPORT
154----------
155The perf c2c report command displays shared data analysis.  It comes in two
156display modes: stdio and tui (default).
157
158The report command workflow is following:
159  - sort all the data based on the cacheline address
160  - store access details for each cacheline
161  - sort all cachelines based on user settings
162  - display data
163
164In general perf report output consist of 2 basic views:
165  1) most expensive cachelines list
166  2) offsets details for each cacheline
167
168For each cacheline in the 1) list we display following data:
169(Both stdio and TUI modes follow the same fields output)
170
171  Index
172  - zero based index to identify the cacheline
173
174  Cacheline
175  - cacheline address (hex number)
176
177  Total records
178  - sum of all cachelines accesses
179
180  Rmt/Lcl Hitm
181  - cacheline percentage of all Remote/Local HITM accesses
182
183  LLC Load Hitm - Total, Lcl, Rmt
184  - count of Total/Local/Remote load HITMs
185
186  Store Reference - Total, L1Hit, L1Miss
187    Total - all store accesses
188    L1Hit - store accesses that hit L1
189    L1Hit - store accesses that missed L1
190
191  Load Dram
192  - count of local and remote DRAM accesses
193
194  LLC Ld Miss
195  - count of all accesses that missed LLC
196
197  Total Loads
198  - sum of all load accesses
199
200  Core Load Hit - FB, L1, L2
201  - count of load hits in FB (Fill Buffer), L1 and L2 cache
202
203  LLC Load Hit - Llc, Rmt
204  - count of LLC and Remote load hits
205
206For each offset in the 2) list we display following data:
207
208  HITM - Rmt, Lcl
209  - % of Remote/Local HITM accesses for given offset within cacheline
210
211  Store Refs - L1 Hit, L1 Miss
212  - % of store accesses that hit/missed L1 for given offset within cacheline
213
214  Data address - Offset
215  - offset address
216
217  Pid
218  - pid of the process responsible for the accesses
219
220  Tid
221  - tid of the process responsible for the accesses
222
223  Code address
224  - code address responsible for the accesses
225
226  cycles - rmt hitm, lcl hitm, load
227    - sum of cycles for given accesses - Remote/Local HITM and generic load
228
229  cpu cnt
230    - number of cpus that participated on the access
231
232  Symbol
233    - code symbol related to the 'Code address' value
234
235  Shared Object
236    - shared object name related to the 'Code address' value
237
238  Source:Line
239    - source information related to the 'Code address' value
240
241  Node
242    - nodes participating on the access (see NODE INFO section)
243
244NODE INFO
245---------
246The 'Node' field displays nodes that accesses given cacheline
247offset. Its output comes in 3 flavors:
248  - node IDs separated by ','
249  - node IDs with stats for each ID, in following format:
250      Node{cpus %hitms %stores}
251  - node IDs with list of affected CPUs in following format:
252      Node{cpu list}
253
254User can switch between above flavors with -N option or
255use 'n' key to interactively switch in TUI mode.
256
257COALESCE
258--------
259User can specify how to sort offsets for cacheline.
260
261Following fields are available and governs the final
262output fields set for caheline offsets output:
263
264  tid   - coalesced by process TIDs
265  pid   - coalesced by process PIDs
266  iaddr - coalesced by code address, following fields are displayed:
267             Code address, Code symbol, Shared Object, Source line
268  dso   - coalesced by shared object
269
270By default the coalescing is setup with 'pid,iaddr'.
271
272STDIO OUTPUT
273------------
274The stdio output displays data on standard output.
275
276Following tables are displayed:
277  Trace Event Information
278  - overall statistics of memory accesses
279
280  Global Shared Cache Line Event Information
281  - overall statistics on shared cachelines
282
283  Shared Data Cache Line Table
284  - list of most expensive cachelines
285
286  Shared Cache Line Distribution Pareto
287  - list of all accessed offsets for each cacheline
288
289TUI OUTPUT
290----------
291The TUI output provides interactive interface to navigate
292through cachelines list and to display offset details.
293
294For details please refer to the help window by pressing '?' key.
295
296CREDITS
297-------
298Although Don Zickus, Dick Fowles and Joe Mario worked together
299to get this implemented, we got lots of early help from Arnaldo
300Carvalho de Melo, Stephane Eranian, Jiri Olsa and Andi Kleen.
301
302C2C BLOG
303--------
304Check Joe's blog on c2c tool for detailed use case explanation:
305  https://joemario.github.io/blog/2016/09/01/c2c-blog/
306
307SEE ALSO
308--------
309linkperf:perf-record[1], linkperf:perf-mem[1]
310