xref: /openbmc/qemu/migration/dirtyrate.c (revision c4601322)
1 /*
2  * Dirtyrate implement code
3  *
4  * Copyright (c) 2020 HUAWEI TECHNOLOGIES CO.,LTD.
5  *
6  * Authors:
7  *  Chuan Zheng <zhengchuan@huawei.com>
8  *
9  * This work is licensed under the terms of the GNU GPL, version 2 or later.
10  * See the COPYING file in the top-level directory.
11  */
12 
13 #include "qemu/osdep.h"
14 #include "qemu/error-report.h"
15 #include <zlib.h>
16 #include "qapi/error.h"
17 #include "cpu.h"
18 #include "exec/ramblock.h"
19 #include "exec/ram_addr.h"
20 #include "qemu/rcu_queue.h"
21 #include "qemu/main-loop.h"
22 #include "qapi/qapi-commands-migration.h"
23 #include "ram.h"
24 #include "trace.h"
25 #include "dirtyrate.h"
26 #include "monitor/hmp.h"
27 #include "monitor/monitor.h"
28 #include "qapi/qmp/qdict.h"
29 #include "sysemu/kvm.h"
30 #include "sysemu/runstate.h"
31 #include "exec/memory.h"
32 
33 /*
34  * total_dirty_pages is procted by BQL and is used
35  * to stat dirty pages during the period of two
36  * memory_global_dirty_log_sync
37  */
38 uint64_t total_dirty_pages;
39 
40 typedef struct DirtyPageRecord {
41     uint64_t start_pages;
42     uint64_t end_pages;
43 } DirtyPageRecord;
44 
45 static int CalculatingState = DIRTY_RATE_STATUS_UNSTARTED;
46 static struct DirtyRateStat DirtyStat;
47 static DirtyRateMeasureMode dirtyrate_mode =
48                 DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING;
49 
50 static int64_t dirty_stat_wait(int64_t msec, int64_t initial_time)
51 {
52     int64_t current_time;
53 
54     current_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
55     if ((current_time - initial_time) >= msec) {
56         msec = current_time - initial_time;
57     } else {
58         g_usleep((msec + initial_time - current_time) * 1000);
59     }
60 
61     return msec;
62 }
63 
64 static inline void record_dirtypages(DirtyPageRecord *dirty_pages,
65                                      CPUState *cpu, bool start)
66 {
67     if (start) {
68         dirty_pages[cpu->cpu_index].start_pages = cpu->dirty_pages;
69     } else {
70         dirty_pages[cpu->cpu_index].end_pages = cpu->dirty_pages;
71     }
72 }
73 
74 static int64_t do_calculate_dirtyrate(DirtyPageRecord dirty_pages,
75                                       int64_t calc_time_ms)
76 {
77     uint64_t memory_size_MB;
78     uint64_t increased_dirty_pages =
79         dirty_pages.end_pages - dirty_pages.start_pages;
80 
81     memory_size_MB = (increased_dirty_pages * TARGET_PAGE_SIZE) >> 20;
82 
83     return memory_size_MB * 1000 / calc_time_ms;
84 }
85 
86 void global_dirty_log_change(unsigned int flag, bool start)
87 {
88     qemu_mutex_lock_iothread();
89     if (start) {
90         memory_global_dirty_log_start(flag);
91     } else {
92         memory_global_dirty_log_stop(flag);
93     }
94     qemu_mutex_unlock_iothread();
95 }
96 
97 /*
98  * global_dirty_log_sync
99  * 1. sync dirty log from kvm
100  * 2. stop dirty tracking if needed.
101  */
102 static void global_dirty_log_sync(unsigned int flag, bool one_shot)
103 {
104     qemu_mutex_lock_iothread();
105     memory_global_dirty_log_sync();
106     if (one_shot) {
107         memory_global_dirty_log_stop(flag);
108     }
109     qemu_mutex_unlock_iothread();
110 }
111 
112 static DirtyPageRecord *vcpu_dirty_stat_alloc(VcpuStat *stat)
113 {
114     CPUState *cpu;
115     int nvcpu = 0;
116 
117     CPU_FOREACH(cpu) {
118         nvcpu++;
119     }
120 
121     stat->nvcpu = nvcpu;
122     stat->rates = g_new0(DirtyRateVcpu, nvcpu);
123 
124     return g_new0(DirtyPageRecord, nvcpu);
125 }
126 
127 static void vcpu_dirty_stat_collect(VcpuStat *stat,
128                                     DirtyPageRecord *records,
129                                     bool start)
130 {
131     CPUState *cpu;
132 
133     CPU_FOREACH(cpu) {
134         record_dirtypages(records, cpu, start);
135     }
136 }
137 
138 int64_t vcpu_calculate_dirtyrate(int64_t calc_time_ms,
139                                  VcpuStat *stat,
140                                  unsigned int flag,
141                                  bool one_shot)
142 {
143     DirtyPageRecord *records;
144     int64_t init_time_ms;
145     int64_t duration;
146     int64_t dirtyrate;
147     int i = 0;
148     unsigned int gen_id;
149 
150 retry:
151     init_time_ms = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
152 
153     WITH_QEMU_LOCK_GUARD(&qemu_cpu_list_lock) {
154         gen_id = cpu_list_generation_id_get();
155         records = vcpu_dirty_stat_alloc(stat);
156         vcpu_dirty_stat_collect(stat, records, true);
157     }
158 
159     duration = dirty_stat_wait(calc_time_ms, init_time_ms);
160 
161     global_dirty_log_sync(flag, one_shot);
162 
163     WITH_QEMU_LOCK_GUARD(&qemu_cpu_list_lock) {
164         if (gen_id != cpu_list_generation_id_get()) {
165             g_free(records);
166             g_free(stat->rates);
167             cpu_list_unlock();
168             goto retry;
169         }
170         vcpu_dirty_stat_collect(stat, records, false);
171     }
172 
173     for (i = 0; i < stat->nvcpu; i++) {
174         dirtyrate = do_calculate_dirtyrate(records[i], duration);
175 
176         stat->rates[i].id = i;
177         stat->rates[i].dirty_rate = dirtyrate;
178 
179         trace_dirtyrate_do_calculate_vcpu(i, dirtyrate);
180     }
181 
182     g_free(records);
183 
184     return duration;
185 }
186 
187 static bool is_sample_period_valid(int64_t sec)
188 {
189     if (sec < MIN_FETCH_DIRTYRATE_TIME_SEC ||
190         sec > MAX_FETCH_DIRTYRATE_TIME_SEC) {
191         return false;
192     }
193 
194     return true;
195 }
196 
197 static bool is_sample_pages_valid(int64_t pages)
198 {
199     return pages >= MIN_SAMPLE_PAGE_COUNT &&
200            pages <= MAX_SAMPLE_PAGE_COUNT;
201 }
202 
203 static int dirtyrate_set_state(int *state, int old_state, int new_state)
204 {
205     assert(new_state < DIRTY_RATE_STATUS__MAX);
206     trace_dirtyrate_set_state(DirtyRateStatus_str(new_state));
207     if (qatomic_cmpxchg(state, old_state, new_state) == old_state) {
208         return 0;
209     } else {
210         return -1;
211     }
212 }
213 
214 static struct DirtyRateInfo *query_dirty_rate_info(void)
215 {
216     int i;
217     int64_t dirty_rate = DirtyStat.dirty_rate;
218     struct DirtyRateInfo *info = g_new0(DirtyRateInfo, 1);
219     DirtyRateVcpuList *head = NULL, **tail = &head;
220 
221     info->status = CalculatingState;
222     info->start_time = DirtyStat.start_time;
223     info->calc_time = DirtyStat.calc_time;
224     info->sample_pages = DirtyStat.sample_pages;
225     info->mode = dirtyrate_mode;
226 
227     if (qatomic_read(&CalculatingState) == DIRTY_RATE_STATUS_MEASURED) {
228         info->has_dirty_rate = true;
229         info->dirty_rate = dirty_rate;
230 
231         if (dirtyrate_mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) {
232             /*
233              * set sample_pages with 0 to indicate page sampling
234              * isn't enabled
235              **/
236             info->sample_pages = 0;
237             info->has_vcpu_dirty_rate = true;
238             for (i = 0; i < DirtyStat.dirty_ring.nvcpu; i++) {
239                 DirtyRateVcpu *rate = g_new0(DirtyRateVcpu, 1);
240                 rate->id = DirtyStat.dirty_ring.rates[i].id;
241                 rate->dirty_rate = DirtyStat.dirty_ring.rates[i].dirty_rate;
242                 QAPI_LIST_APPEND(tail, rate);
243             }
244             info->vcpu_dirty_rate = head;
245         }
246 
247         if (dirtyrate_mode == DIRTY_RATE_MEASURE_MODE_DIRTY_BITMAP) {
248             info->sample_pages = 0;
249         }
250     }
251 
252     trace_query_dirty_rate_info(DirtyRateStatus_str(CalculatingState));
253 
254     return info;
255 }
256 
257 static void init_dirtyrate_stat(int64_t start_time,
258                                 struct DirtyRateConfig config)
259 {
260     DirtyStat.dirty_rate = -1;
261     DirtyStat.start_time = start_time;
262     DirtyStat.calc_time = config.sample_period_seconds;
263     DirtyStat.sample_pages = config.sample_pages_per_gigabytes;
264 
265     switch (config.mode) {
266     case DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING:
267         DirtyStat.page_sampling.total_dirty_samples = 0;
268         DirtyStat.page_sampling.total_sample_count = 0;
269         DirtyStat.page_sampling.total_block_mem_MB = 0;
270         break;
271     case DIRTY_RATE_MEASURE_MODE_DIRTY_RING:
272         DirtyStat.dirty_ring.nvcpu = -1;
273         DirtyStat.dirty_ring.rates = NULL;
274         break;
275     default:
276         break;
277     }
278 }
279 
280 static void cleanup_dirtyrate_stat(struct DirtyRateConfig config)
281 {
282     /* last calc-dirty-rate qmp use dirty ring mode */
283     if (dirtyrate_mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) {
284         free(DirtyStat.dirty_ring.rates);
285         DirtyStat.dirty_ring.rates = NULL;
286     }
287 }
288 
289 static void update_dirtyrate_stat(struct RamblockDirtyInfo *info)
290 {
291     DirtyStat.page_sampling.total_dirty_samples += info->sample_dirty_count;
292     DirtyStat.page_sampling.total_sample_count += info->sample_pages_count;
293     /* size of total pages in MB */
294     DirtyStat.page_sampling.total_block_mem_MB += (info->ramblock_pages *
295                                                    TARGET_PAGE_SIZE) >> 20;
296 }
297 
298 static void update_dirtyrate(uint64_t msec)
299 {
300     uint64_t dirtyrate;
301     uint64_t total_dirty_samples = DirtyStat.page_sampling.total_dirty_samples;
302     uint64_t total_sample_count = DirtyStat.page_sampling.total_sample_count;
303     uint64_t total_block_mem_MB = DirtyStat.page_sampling.total_block_mem_MB;
304 
305     dirtyrate = total_dirty_samples * total_block_mem_MB *
306                 1000 / (total_sample_count * msec);
307 
308     DirtyStat.dirty_rate = dirtyrate;
309 }
310 
311 /*
312  * get hash result for the sampled memory with length of TARGET_PAGE_SIZE
313  * in ramblock, which starts from ramblock base address.
314  */
315 static uint32_t get_ramblock_vfn_hash(struct RamblockDirtyInfo *info,
316                                       uint64_t vfn)
317 {
318     uint32_t crc;
319 
320     crc = crc32(0, (info->ramblock_addr +
321                 vfn * TARGET_PAGE_SIZE), TARGET_PAGE_SIZE);
322 
323     trace_get_ramblock_vfn_hash(info->idstr, vfn, crc);
324     return crc;
325 }
326 
327 static bool save_ramblock_hash(struct RamblockDirtyInfo *info)
328 {
329     unsigned int sample_pages_count;
330     int i;
331     GRand *rand;
332 
333     sample_pages_count = info->sample_pages_count;
334 
335     /* ramblock size less than one page, return success to skip this ramblock */
336     if (unlikely(info->ramblock_pages == 0 || sample_pages_count == 0)) {
337         return true;
338     }
339 
340     info->hash_result = g_try_malloc0_n(sample_pages_count,
341                                         sizeof(uint32_t));
342     if (!info->hash_result) {
343         return false;
344     }
345 
346     info->sample_page_vfn = g_try_malloc0_n(sample_pages_count,
347                                             sizeof(uint64_t));
348     if (!info->sample_page_vfn) {
349         g_free(info->hash_result);
350         return false;
351     }
352 
353     rand  = g_rand_new();
354     for (i = 0; i < sample_pages_count; i++) {
355         info->sample_page_vfn[i] = g_rand_int_range(rand, 0,
356                                                     info->ramblock_pages - 1);
357         info->hash_result[i] = get_ramblock_vfn_hash(info,
358                                                      info->sample_page_vfn[i]);
359     }
360     g_rand_free(rand);
361 
362     return true;
363 }
364 
365 static void get_ramblock_dirty_info(RAMBlock *block,
366                                     struct RamblockDirtyInfo *info,
367                                     struct DirtyRateConfig *config)
368 {
369     uint64_t sample_pages_per_gigabytes = config->sample_pages_per_gigabytes;
370 
371     /* Right shift 30 bits to calc ramblock size in GB */
372     info->sample_pages_count = (qemu_ram_get_used_length(block) *
373                                 sample_pages_per_gigabytes) >> 30;
374     /* Right shift TARGET_PAGE_BITS to calc page count */
375     info->ramblock_pages = qemu_ram_get_used_length(block) >>
376                            TARGET_PAGE_BITS;
377     info->ramblock_addr = qemu_ram_get_host_addr(block);
378     strcpy(info->idstr, qemu_ram_get_idstr(block));
379 }
380 
381 static void free_ramblock_dirty_info(struct RamblockDirtyInfo *infos, int count)
382 {
383     int i;
384 
385     if (!infos) {
386         return;
387     }
388 
389     for (i = 0; i < count; i++) {
390         g_free(infos[i].sample_page_vfn);
391         g_free(infos[i].hash_result);
392     }
393     g_free(infos);
394 }
395 
396 static bool skip_sample_ramblock(RAMBlock *block)
397 {
398     /*
399      * Sample only blocks larger than MIN_RAMBLOCK_SIZE.
400      */
401     if (qemu_ram_get_used_length(block) < (MIN_RAMBLOCK_SIZE << 10)) {
402         trace_skip_sample_ramblock(block->idstr,
403                                    qemu_ram_get_used_length(block));
404         return true;
405     }
406 
407     return false;
408 }
409 
410 static bool record_ramblock_hash_info(struct RamblockDirtyInfo **block_dinfo,
411                                       struct DirtyRateConfig config,
412                                       int *block_count)
413 {
414     struct RamblockDirtyInfo *info = NULL;
415     struct RamblockDirtyInfo *dinfo = NULL;
416     RAMBlock *block = NULL;
417     int total_count = 0;
418     int index = 0;
419     bool ret = false;
420 
421     RAMBLOCK_FOREACH_MIGRATABLE(block) {
422         if (skip_sample_ramblock(block)) {
423             continue;
424         }
425         total_count++;
426     }
427 
428     dinfo = g_try_malloc0_n(total_count, sizeof(struct RamblockDirtyInfo));
429     if (dinfo == NULL) {
430         goto out;
431     }
432 
433     RAMBLOCK_FOREACH_MIGRATABLE(block) {
434         if (skip_sample_ramblock(block)) {
435             continue;
436         }
437         if (index >= total_count) {
438             break;
439         }
440         info = &dinfo[index];
441         get_ramblock_dirty_info(block, info, &config);
442         if (!save_ramblock_hash(info)) {
443             goto out;
444         }
445         index++;
446     }
447     ret = true;
448 
449 out:
450     *block_count = index;
451     *block_dinfo = dinfo;
452     return ret;
453 }
454 
455 static void calc_page_dirty_rate(struct RamblockDirtyInfo *info)
456 {
457     uint32_t crc;
458     int i;
459 
460     for (i = 0; i < info->sample_pages_count; i++) {
461         crc = get_ramblock_vfn_hash(info, info->sample_page_vfn[i]);
462         if (crc != info->hash_result[i]) {
463             trace_calc_page_dirty_rate(info->idstr, crc, info->hash_result[i]);
464             info->sample_dirty_count++;
465         }
466     }
467 }
468 
469 static struct RamblockDirtyInfo *
470 find_block_matched(RAMBlock *block, int count,
471                   struct RamblockDirtyInfo *infos)
472 {
473     int i;
474 
475     for (i = 0; i < count; i++) {
476         if (!strcmp(infos[i].idstr, qemu_ram_get_idstr(block))) {
477             break;
478         }
479     }
480 
481     if (i == count) {
482         return NULL;
483     }
484 
485     if (infos[i].ramblock_addr != qemu_ram_get_host_addr(block) ||
486         infos[i].ramblock_pages !=
487             (qemu_ram_get_used_length(block) >> TARGET_PAGE_BITS)) {
488         trace_find_page_matched(block->idstr);
489         return NULL;
490     }
491 
492     return &infos[i];
493 }
494 
495 static bool compare_page_hash_info(struct RamblockDirtyInfo *info,
496                                   int block_count)
497 {
498     struct RamblockDirtyInfo *block_dinfo = NULL;
499     RAMBlock *block = NULL;
500 
501     RAMBLOCK_FOREACH_MIGRATABLE(block) {
502         if (skip_sample_ramblock(block)) {
503             continue;
504         }
505         block_dinfo = find_block_matched(block, block_count, info);
506         if (block_dinfo == NULL) {
507             continue;
508         }
509         calc_page_dirty_rate(block_dinfo);
510         update_dirtyrate_stat(block_dinfo);
511     }
512 
513     if (DirtyStat.page_sampling.total_sample_count == 0) {
514         return false;
515     }
516 
517     return true;
518 }
519 
520 static inline void record_dirtypages_bitmap(DirtyPageRecord *dirty_pages,
521                                             bool start)
522 {
523     if (start) {
524         dirty_pages->start_pages = total_dirty_pages;
525     } else {
526         dirty_pages->end_pages = total_dirty_pages;
527     }
528 }
529 
530 static inline void dirtyrate_manual_reset_protect(void)
531 {
532     RAMBlock *block = NULL;
533 
534     WITH_RCU_READ_LOCK_GUARD() {
535         RAMBLOCK_FOREACH_MIGRATABLE(block) {
536             memory_region_clear_dirty_bitmap(block->mr, 0,
537                                              block->used_length);
538         }
539     }
540 }
541 
542 static void calculate_dirtyrate_dirty_bitmap(struct DirtyRateConfig config)
543 {
544     int64_t msec = 0;
545     int64_t start_time;
546     DirtyPageRecord dirty_pages;
547 
548     qemu_mutex_lock_iothread();
549     memory_global_dirty_log_start(GLOBAL_DIRTY_DIRTY_RATE);
550 
551     /*
552      * 1'round of log sync may return all 1 bits with
553      * KVM_DIRTY_LOG_INITIALLY_SET enable
554      * skip it unconditionally and start dirty tracking
555      * from 2'round of log sync
556      */
557     memory_global_dirty_log_sync();
558 
559     /*
560      * reset page protect manually and unconditionally.
561      * this make sure kvm dirty log be cleared if
562      * KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE cap is enabled.
563      */
564     dirtyrate_manual_reset_protect();
565     qemu_mutex_unlock_iothread();
566 
567     record_dirtypages_bitmap(&dirty_pages, true);
568 
569     start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
570     DirtyStat.start_time = start_time / 1000;
571 
572     msec = config.sample_period_seconds * 1000;
573     msec = dirty_stat_wait(msec, start_time);
574     DirtyStat.calc_time = msec / 1000;
575 
576     /*
577      * do two things.
578      * 1. fetch dirty bitmap from kvm
579      * 2. stop dirty tracking
580      */
581     global_dirty_log_sync(GLOBAL_DIRTY_DIRTY_RATE, true);
582 
583     record_dirtypages_bitmap(&dirty_pages, false);
584 
585     DirtyStat.dirty_rate = do_calculate_dirtyrate(dirty_pages, msec);
586 }
587 
588 static void calculate_dirtyrate_dirty_ring(struct DirtyRateConfig config)
589 {
590     int64_t duration;
591     uint64_t dirtyrate = 0;
592     uint64_t dirtyrate_sum = 0;
593     int i = 0;
594 
595     /* start log sync */
596     global_dirty_log_change(GLOBAL_DIRTY_DIRTY_RATE, true);
597 
598     DirtyStat.start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
599 
600     /* calculate vcpu dirtyrate */
601     duration = vcpu_calculate_dirtyrate(config.sample_period_seconds * 1000,
602                                         &DirtyStat.dirty_ring,
603                                         GLOBAL_DIRTY_DIRTY_RATE,
604                                         true);
605 
606     DirtyStat.calc_time = duration / 1000;
607 
608     /* calculate vm dirtyrate */
609     for (i = 0; i < DirtyStat.dirty_ring.nvcpu; i++) {
610         dirtyrate = DirtyStat.dirty_ring.rates[i].dirty_rate;
611         DirtyStat.dirty_ring.rates[i].dirty_rate = dirtyrate;
612         dirtyrate_sum += dirtyrate;
613     }
614 
615     DirtyStat.dirty_rate = dirtyrate_sum;
616 }
617 
618 static void calculate_dirtyrate_sample_vm(struct DirtyRateConfig config)
619 {
620     struct RamblockDirtyInfo *block_dinfo = NULL;
621     int block_count = 0;
622     int64_t msec = 0;
623     int64_t initial_time;
624 
625     rcu_read_lock();
626     initial_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
627     if (!record_ramblock_hash_info(&block_dinfo, config, &block_count)) {
628         goto out;
629     }
630     rcu_read_unlock();
631 
632     msec = config.sample_period_seconds * 1000;
633     msec = dirty_stat_wait(msec, initial_time);
634     DirtyStat.start_time = initial_time / 1000;
635     DirtyStat.calc_time = msec / 1000;
636 
637     rcu_read_lock();
638     if (!compare_page_hash_info(block_dinfo, block_count)) {
639         goto out;
640     }
641 
642     update_dirtyrate(msec);
643 
644 out:
645     rcu_read_unlock();
646     free_ramblock_dirty_info(block_dinfo, block_count);
647 }
648 
649 static void calculate_dirtyrate(struct DirtyRateConfig config)
650 {
651     if (config.mode == DIRTY_RATE_MEASURE_MODE_DIRTY_BITMAP) {
652         calculate_dirtyrate_dirty_bitmap(config);
653     } else if (config.mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) {
654         calculate_dirtyrate_dirty_ring(config);
655     } else {
656         calculate_dirtyrate_sample_vm(config);
657     }
658 
659     trace_dirtyrate_calculate(DirtyStat.dirty_rate);
660 }
661 
662 void *get_dirtyrate_thread(void *arg)
663 {
664     struct DirtyRateConfig config = *(struct DirtyRateConfig *)arg;
665     int ret;
666     rcu_register_thread();
667 
668     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_UNSTARTED,
669                               DIRTY_RATE_STATUS_MEASURING);
670     if (ret == -1) {
671         error_report("change dirtyrate state failed.");
672         return NULL;
673     }
674 
675     calculate_dirtyrate(config);
676 
677     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_MEASURING,
678                               DIRTY_RATE_STATUS_MEASURED);
679     if (ret == -1) {
680         error_report("change dirtyrate state failed.");
681     }
682 
683     rcu_unregister_thread();
684     return NULL;
685 }
686 
687 void qmp_calc_dirty_rate(int64_t calc_time,
688                          bool has_sample_pages,
689                          int64_t sample_pages,
690                          bool has_mode,
691                          DirtyRateMeasureMode mode,
692                          Error **errp)
693 {
694     static struct DirtyRateConfig config;
695     QemuThread thread;
696     int ret;
697     int64_t start_time;
698 
699     /*
700      * If the dirty rate is already being measured, don't attempt to start.
701      */
702     if (qatomic_read(&CalculatingState) == DIRTY_RATE_STATUS_MEASURING) {
703         error_setg(errp, "the dirty rate is already being measured.");
704         return;
705     }
706 
707     if (!is_sample_period_valid(calc_time)) {
708         error_setg(errp, "calc-time is out of range[%d, %d].",
709                          MIN_FETCH_DIRTYRATE_TIME_SEC,
710                          MAX_FETCH_DIRTYRATE_TIME_SEC);
711         return;
712     }
713 
714     if (!has_mode) {
715         mode =  DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING;
716     }
717 
718     if (has_sample_pages && mode != DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING) {
719         error_setg(errp, "sample-pages is used only in page-sampling mode");
720         return;
721     }
722 
723     if (has_sample_pages) {
724         if (!is_sample_pages_valid(sample_pages)) {
725             error_setg(errp, "sample-pages is out of range[%d, %d].",
726                             MIN_SAMPLE_PAGE_COUNT,
727                             MAX_SAMPLE_PAGE_COUNT);
728             return;
729         }
730     } else {
731         sample_pages = DIRTYRATE_DEFAULT_SAMPLE_PAGES;
732     }
733 
734     /*
735      * dirty ring mode only works when kvm dirty ring is enabled.
736      * on the contrary, dirty bitmap mode is not.
737      */
738     if (((mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) &&
739         !kvm_dirty_ring_enabled()) ||
740         ((mode == DIRTY_RATE_MEASURE_MODE_DIRTY_BITMAP) &&
741          kvm_dirty_ring_enabled())) {
742         error_setg(errp, "mode %s is not enabled, use other method instead.",
743                          DirtyRateMeasureMode_str(mode));
744          return;
745     }
746 
747     /*
748      * Init calculation state as unstarted.
749      */
750     ret = dirtyrate_set_state(&CalculatingState, CalculatingState,
751                               DIRTY_RATE_STATUS_UNSTARTED);
752     if (ret == -1) {
753         error_setg(errp, "init dirty rate calculation state failed.");
754         return;
755     }
756 
757     config.sample_period_seconds = calc_time;
758     config.sample_pages_per_gigabytes = sample_pages;
759     config.mode = mode;
760 
761     cleanup_dirtyrate_stat(config);
762 
763     /*
764      * update dirty rate mode so that we can figure out what mode has
765      * been used in last calculation
766      **/
767     dirtyrate_mode = mode;
768 
769     start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
770     init_dirtyrate_stat(start_time, config);
771 
772     qemu_thread_create(&thread, "get_dirtyrate", get_dirtyrate_thread,
773                        (void *)&config, QEMU_THREAD_DETACHED);
774 }
775 
776 struct DirtyRateInfo *qmp_query_dirty_rate(Error **errp)
777 {
778     return query_dirty_rate_info();
779 }
780 
781 void hmp_info_dirty_rate(Monitor *mon, const QDict *qdict)
782 {
783     DirtyRateInfo *info = query_dirty_rate_info();
784 
785     monitor_printf(mon, "Status: %s\n",
786                    DirtyRateStatus_str(info->status));
787     monitor_printf(mon, "Start Time: %"PRIi64" (ms)\n",
788                    info->start_time);
789     if (info->mode == DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING) {
790         monitor_printf(mon, "Sample Pages: %"PRIu64" (per GB)\n",
791                        info->sample_pages);
792     }
793     monitor_printf(mon, "Period: %"PRIi64" (sec)\n",
794                    info->calc_time);
795     monitor_printf(mon, "Mode: %s\n",
796                    DirtyRateMeasureMode_str(info->mode));
797     monitor_printf(mon, "Dirty rate: ");
798     if (info->has_dirty_rate) {
799         monitor_printf(mon, "%"PRIi64" (MB/s)\n", info->dirty_rate);
800         if (info->has_vcpu_dirty_rate) {
801             DirtyRateVcpuList *rate, *head = info->vcpu_dirty_rate;
802             for (rate = head; rate != NULL; rate = rate->next) {
803                 monitor_printf(mon, "vcpu[%"PRIi64"], Dirty rate: %"PRIi64
804                                " (MB/s)\n", rate->value->id,
805                                rate->value->dirty_rate);
806             }
807         }
808     } else {
809         monitor_printf(mon, "(not ready)\n");
810     }
811 
812     qapi_free_DirtyRateVcpuList(info->vcpu_dirty_rate);
813     g_free(info);
814 }
815 
816 void hmp_calc_dirty_rate(Monitor *mon, const QDict *qdict)
817 {
818     int64_t sec = qdict_get_try_int(qdict, "second", 0);
819     int64_t sample_pages = qdict_get_try_int(qdict, "sample_pages_per_GB", -1);
820     bool has_sample_pages = (sample_pages != -1);
821     bool dirty_ring = qdict_get_try_bool(qdict, "dirty_ring", false);
822     bool dirty_bitmap = qdict_get_try_bool(qdict, "dirty_bitmap", false);
823     DirtyRateMeasureMode mode = DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING;
824     Error *err = NULL;
825 
826     if (!sec) {
827         monitor_printf(mon, "Incorrect period length specified!\n");
828         return;
829     }
830 
831     if (dirty_ring && dirty_bitmap) {
832         monitor_printf(mon, "Either dirty ring or dirty bitmap "
833                        "can be specified!\n");
834         return;
835     }
836 
837     if (dirty_bitmap) {
838         mode = DIRTY_RATE_MEASURE_MODE_DIRTY_BITMAP;
839     } else if (dirty_ring) {
840         mode = DIRTY_RATE_MEASURE_MODE_DIRTY_RING;
841     }
842 
843     qmp_calc_dirty_rate(sec, has_sample_pages, sample_pages, true,
844                         mode, &err);
845     if (err) {
846         hmp_handle_error(mon, err);
847         return;
848     }
849 
850     monitor_printf(mon, "Starting dirty rate measurement with period %"PRIi64
851                    " seconds\n", sec);
852     monitor_printf(mon, "[Please use 'info dirty_rate' to check results]\n");
853 }
854