xref: /openbmc/qemu/migration/dirtyrate.c (revision b7bc6b18) 
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 <zlib.h>
15 #include "qapi/error.h"
16 #include "cpu.h"
17 #include "exec/ramblock.h"
18 #include "qemu/rcu_queue.h"
19 #include "qemu/main-loop.h"
20 #include "qapi/qapi-commands-migration.h"
21 #include "ram.h"
22 #include "trace.h"
23 #include "dirtyrate.h"
24 #include "monitor/hmp.h"
25 #include "monitor/monitor.h"
26 #include "qapi/qmp/qdict.h"
27 #include "sysemu/kvm.h"
28 #include "sysemu/runstate.h"
29 #include "exec/memory.h"
30 
31 typedef struct DirtyPageRecord {
32     uint64_t start_pages;
33     uint64_t end_pages;
34 } DirtyPageRecord;
35 
36 static int CalculatingState = DIRTY_RATE_STATUS_UNSTARTED;
37 static struct DirtyRateStat DirtyStat;
38 static DirtyRateMeasureMode dirtyrate_mode =
39                 DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING;
40 
41 static int64_t set_sample_page_period(int64_t msec, int64_t initial_time)
42 {
43     int64_t current_time;
44 
45     current_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
46     if ((current_time - initial_time) >= msec) {
47         msec = current_time - initial_time;
48     } else {
49         g_usleep((msec + initial_time - current_time) * 1000);
50     }
51 
52     return msec;
53 }
54 
55 static bool is_sample_period_valid(int64_t sec)
56 {
57     if (sec < MIN_FETCH_DIRTYRATE_TIME_SEC ||
58         sec > MAX_FETCH_DIRTYRATE_TIME_SEC) {
59         return false;
60     }
61 
62     return true;
63 }
64 
65 static bool is_sample_pages_valid(int64_t pages)
66 {
67     return pages >= MIN_SAMPLE_PAGE_COUNT &&
68            pages <= MAX_SAMPLE_PAGE_COUNT;
69 }
70 
71 static int dirtyrate_set_state(int *state, int old_state, int new_state)
72 {
73     assert(new_state < DIRTY_RATE_STATUS__MAX);
74     trace_dirtyrate_set_state(DirtyRateStatus_str(new_state));
75     if (qatomic_cmpxchg(state, old_state, new_state) == old_state) {
76         return 0;
77     } else {
78         return -1;
79     }
80 }
81 
82 static struct DirtyRateInfo *query_dirty_rate_info(void)
83 {
84     int i;
85     int64_t dirty_rate = DirtyStat.dirty_rate;
86     struct DirtyRateInfo *info = g_malloc0(sizeof(DirtyRateInfo));
87     DirtyRateVcpuList *head = NULL, **tail = &head;
88 
89     info->status = CalculatingState;
90     info->start_time = DirtyStat.start_time;
91     info->calc_time = DirtyStat.calc_time;
92     info->sample_pages = DirtyStat.sample_pages;
93     info->mode = dirtyrate_mode;
94 
95     if (qatomic_read(&CalculatingState) == DIRTY_RATE_STATUS_MEASURED) {
96         info->has_dirty_rate = true;
97         info->dirty_rate = dirty_rate;
98 
99         if (dirtyrate_mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) {
100             /*
101              * set sample_pages with 0 to indicate page sampling
102              * isn't enabled
103              **/
104             info->sample_pages = 0;
105             info->has_vcpu_dirty_rate = true;
106             for (i = 0; i < DirtyStat.dirty_ring.nvcpu; i++) {
107                 DirtyRateVcpu *rate = g_malloc0(sizeof(DirtyRateVcpu));
108                 rate->id = DirtyStat.dirty_ring.rates[i].id;
109                 rate->dirty_rate = DirtyStat.dirty_ring.rates[i].dirty_rate;
110                 QAPI_LIST_APPEND(tail, rate);
111             }
112             info->vcpu_dirty_rate = head;
113         }
114     }
115 
116     trace_query_dirty_rate_info(DirtyRateStatus_str(CalculatingState));
117 
118     return info;
119 }
120 
121 static void init_dirtyrate_stat(int64_t start_time,
122                                 struct DirtyRateConfig config)
123 {
124     DirtyStat.dirty_rate = -1;
125     DirtyStat.start_time = start_time;
126     DirtyStat.calc_time = config.sample_period_seconds;
127     DirtyStat.sample_pages = config.sample_pages_per_gigabytes;
128 
129     switch (config.mode) {
130     case DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING:
131         DirtyStat.page_sampling.total_dirty_samples = 0;
132         DirtyStat.page_sampling.total_sample_count = 0;
133         DirtyStat.page_sampling.total_block_mem_MB = 0;
134         break;
135     case DIRTY_RATE_MEASURE_MODE_DIRTY_RING:
136         DirtyStat.dirty_ring.nvcpu = -1;
137         DirtyStat.dirty_ring.rates = NULL;
138         break;
139     default:
140         break;
141     }
142 }
143 
144 static void cleanup_dirtyrate_stat(struct DirtyRateConfig config)
145 {
146     /* last calc-dirty-rate qmp use dirty ring mode */
147     if (dirtyrate_mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) {
148         free(DirtyStat.dirty_ring.rates);
149         DirtyStat.dirty_ring.rates = NULL;
150     }
151 }
152 
153 static void update_dirtyrate_stat(struct RamblockDirtyInfo *info)
154 {
155     DirtyStat.page_sampling.total_dirty_samples += info->sample_dirty_count;
156     DirtyStat.page_sampling.total_sample_count += info->sample_pages_count;
157     /* size of total pages in MB */
158     DirtyStat.page_sampling.total_block_mem_MB += (info->ramblock_pages *
159                                                    TARGET_PAGE_SIZE) >> 20;
160 }
161 
162 static void update_dirtyrate(uint64_t msec)
163 {
164     uint64_t dirtyrate;
165     uint64_t total_dirty_samples = DirtyStat.page_sampling.total_dirty_samples;
166     uint64_t total_sample_count = DirtyStat.page_sampling.total_sample_count;
167     uint64_t total_block_mem_MB = DirtyStat.page_sampling.total_block_mem_MB;
168 
169     dirtyrate = total_dirty_samples * total_block_mem_MB *
170                 1000 / (total_sample_count * msec);
171 
172     DirtyStat.dirty_rate = dirtyrate;
173 }
174 
175 /*
176  * get hash result for the sampled memory with length of TARGET_PAGE_SIZE
177  * in ramblock, which starts from ramblock base address.
178  */
179 static uint32_t get_ramblock_vfn_hash(struct RamblockDirtyInfo *info,
180                                       uint64_t vfn)
181 {
182     uint32_t crc;
183 
184     crc = crc32(0, (info->ramblock_addr +
185                 vfn * TARGET_PAGE_SIZE), TARGET_PAGE_SIZE);
186 
187     trace_get_ramblock_vfn_hash(info->idstr, vfn, crc);
188     return crc;
189 }
190 
191 static bool save_ramblock_hash(struct RamblockDirtyInfo *info)
192 {
193     unsigned int sample_pages_count;
194     int i;
195     GRand *rand;
196 
197     sample_pages_count = info->sample_pages_count;
198 
199     /* ramblock size less than one page, return success to skip this ramblock */
200     if (unlikely(info->ramblock_pages == 0 || sample_pages_count == 0)) {
201         return true;
202     }
203 
204     info->hash_result = g_try_malloc0_n(sample_pages_count,
205                                         sizeof(uint32_t));
206     if (!info->hash_result) {
207         return false;
208     }
209 
210     info->sample_page_vfn = g_try_malloc0_n(sample_pages_count,
211                                             sizeof(uint64_t));
212     if (!info->sample_page_vfn) {
213         g_free(info->hash_result);
214         return false;
215     }
216 
217     rand  = g_rand_new();
218     for (i = 0; i < sample_pages_count; i++) {
219         info->sample_page_vfn[i] = g_rand_int_range(rand, 0,
220                                                     info->ramblock_pages - 1);
221         info->hash_result[i] = get_ramblock_vfn_hash(info,
222                                                      info->sample_page_vfn[i]);
223     }
224     g_rand_free(rand);
225 
226     return true;
227 }
228 
229 static void get_ramblock_dirty_info(RAMBlock *block,
230                                     struct RamblockDirtyInfo *info,
231                                     struct DirtyRateConfig *config)
232 {
233     uint64_t sample_pages_per_gigabytes = config->sample_pages_per_gigabytes;
234 
235     /* Right shift 30 bits to calc ramblock size in GB */
236     info->sample_pages_count = (qemu_ram_get_used_length(block) *
237                                 sample_pages_per_gigabytes) >> 30;
238     /* Right shift TARGET_PAGE_BITS to calc page count */
239     info->ramblock_pages = qemu_ram_get_used_length(block) >>
240                            TARGET_PAGE_BITS;
241     info->ramblock_addr = qemu_ram_get_host_addr(block);
242     strcpy(info->idstr, qemu_ram_get_idstr(block));
243 }
244 
245 static void free_ramblock_dirty_info(struct RamblockDirtyInfo *infos, int count)
246 {
247     int i;
248 
249     if (!infos) {
250         return;
251     }
252 
253     for (i = 0; i < count; i++) {
254         g_free(infos[i].sample_page_vfn);
255         g_free(infos[i].hash_result);
256     }
257     g_free(infos);
258 }
259 
260 static bool skip_sample_ramblock(RAMBlock *block)
261 {
262     /*
263      * Sample only blocks larger than MIN_RAMBLOCK_SIZE.
264      */
265     if (qemu_ram_get_used_length(block) < (MIN_RAMBLOCK_SIZE << 10)) {
266         trace_skip_sample_ramblock(block->idstr,
267                                    qemu_ram_get_used_length(block));
268         return true;
269     }
270 
271     return false;
272 }
273 
274 static bool record_ramblock_hash_info(struct RamblockDirtyInfo **block_dinfo,
275                                       struct DirtyRateConfig config,
276                                       int *block_count)
277 {
278     struct RamblockDirtyInfo *info = NULL;
279     struct RamblockDirtyInfo *dinfo = NULL;
280     RAMBlock *block = NULL;
281     int total_count = 0;
282     int index = 0;
283     bool ret = false;
284 
285     RAMBLOCK_FOREACH_MIGRATABLE(block) {
286         if (skip_sample_ramblock(block)) {
287             continue;
288         }
289         total_count++;
290     }
291 
292     dinfo = g_try_malloc0_n(total_count, sizeof(struct RamblockDirtyInfo));
293     if (dinfo == NULL) {
294         goto out;
295     }
296 
297     RAMBLOCK_FOREACH_MIGRATABLE(block) {
298         if (skip_sample_ramblock(block)) {
299             continue;
300         }
301         if (index >= total_count) {
302             break;
303         }
304         info = &dinfo[index];
305         get_ramblock_dirty_info(block, info, &config);
306         if (!save_ramblock_hash(info)) {
307             goto out;
308         }
309         index++;
310     }
311     ret = true;
312 
313 out:
314     *block_count = index;
315     *block_dinfo = dinfo;
316     return ret;
317 }
318 
319 static void calc_page_dirty_rate(struct RamblockDirtyInfo *info)
320 {
321     uint32_t crc;
322     int i;
323 
324     for (i = 0; i < info->sample_pages_count; i++) {
325         crc = get_ramblock_vfn_hash(info, info->sample_page_vfn[i]);
326         if (crc != info->hash_result[i]) {
327             trace_calc_page_dirty_rate(info->idstr, crc, info->hash_result[i]);
328             info->sample_dirty_count++;
329         }
330     }
331 }
332 
333 static struct RamblockDirtyInfo *
334 find_block_matched(RAMBlock *block, int count,
335                   struct RamblockDirtyInfo *infos)
336 {
337     int i;
338     struct RamblockDirtyInfo *matched;
339 
340     for (i = 0; i < count; i++) {
341         if (!strcmp(infos[i].idstr, qemu_ram_get_idstr(block))) {
342             break;
343         }
344     }
345 
346     if (i == count) {
347         return NULL;
348     }
349 
350     if (infos[i].ramblock_addr != qemu_ram_get_host_addr(block) ||
351         infos[i].ramblock_pages !=
352             (qemu_ram_get_used_length(block) >> TARGET_PAGE_BITS)) {
353         trace_find_page_matched(block->idstr);
354         return NULL;
355     }
356 
357     matched = &infos[i];
358 
359     return matched;
360 }
361 
362 static bool compare_page_hash_info(struct RamblockDirtyInfo *info,
363                                   int block_count)
364 {
365     struct RamblockDirtyInfo *block_dinfo = NULL;
366     RAMBlock *block = NULL;
367 
368     RAMBLOCK_FOREACH_MIGRATABLE(block) {
369         if (skip_sample_ramblock(block)) {
370             continue;
371         }
372         block_dinfo = find_block_matched(block, block_count, info);
373         if (block_dinfo == NULL) {
374             continue;
375         }
376         calc_page_dirty_rate(block_dinfo);
377         update_dirtyrate_stat(block_dinfo);
378     }
379 
380     if (DirtyStat.page_sampling.total_sample_count == 0) {
381         return false;
382     }
383 
384     return true;
385 }
386 
387 static inline void record_dirtypages(DirtyPageRecord *dirty_pages,
388                                      CPUState *cpu, bool start)
389 {
390     if (start) {
391         dirty_pages[cpu->cpu_index].start_pages = cpu->dirty_pages;
392     } else {
393         dirty_pages[cpu->cpu_index].end_pages = cpu->dirty_pages;
394     }
395 }
396 
397 static void dirtyrate_global_dirty_log_start(void)
398 {
399     qemu_mutex_lock_iothread();
400     memory_global_dirty_log_start(GLOBAL_DIRTY_DIRTY_RATE);
401     qemu_mutex_unlock_iothread();
402 }
403 
404 static void dirtyrate_global_dirty_log_stop(void)
405 {
406     qemu_mutex_lock_iothread();
407     memory_global_dirty_log_sync();
408     memory_global_dirty_log_stop(GLOBAL_DIRTY_DIRTY_RATE);
409     qemu_mutex_unlock_iothread();
410 }
411 
412 static int64_t do_calculate_dirtyrate_vcpu(DirtyPageRecord dirty_pages)
413 {
414     uint64_t memory_size_MB;
415     int64_t time_s;
416     uint64_t increased_dirty_pages =
417         dirty_pages.end_pages - dirty_pages.start_pages;
418 
419     memory_size_MB = (increased_dirty_pages * TARGET_PAGE_SIZE) >> 20;
420     time_s = DirtyStat.calc_time;
421 
422     return memory_size_MB / time_s;
423 }
424 
425 static void calculate_dirtyrate_dirty_ring(struct DirtyRateConfig config)
426 {
427     CPUState *cpu;
428     int64_t msec = 0;
429     int64_t start_time;
430     uint64_t dirtyrate = 0;
431     uint64_t dirtyrate_sum = 0;
432     DirtyPageRecord *dirty_pages;
433     int nvcpu = 0;
434     int i = 0;
435 
436     CPU_FOREACH(cpu) {
437         nvcpu++;
438     }
439 
440     dirty_pages = malloc(sizeof(*dirty_pages) * nvcpu);
441 
442     DirtyStat.dirty_ring.nvcpu = nvcpu;
443     DirtyStat.dirty_ring.rates = malloc(sizeof(DirtyRateVcpu) * nvcpu);
444 
445     dirtyrate_global_dirty_log_start();
446 
447     CPU_FOREACH(cpu) {
448         record_dirtypages(dirty_pages, cpu, true);
449     }
450 
451     start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
452     DirtyStat.start_time = start_time / 1000;
453 
454     msec = config.sample_period_seconds * 1000;
455     msec = set_sample_page_period(msec, start_time);
456     DirtyStat.calc_time = msec / 1000;
457 
458     dirtyrate_global_dirty_log_stop();
459 
460     CPU_FOREACH(cpu) {
461         record_dirtypages(dirty_pages, cpu, false);
462     }
463 
464     for (i = 0; i < DirtyStat.dirty_ring.nvcpu; i++) {
465         dirtyrate = do_calculate_dirtyrate_vcpu(dirty_pages[i]);
466         trace_dirtyrate_do_calculate_vcpu(i, dirtyrate);
467 
468         DirtyStat.dirty_ring.rates[i].id = i;
469         DirtyStat.dirty_ring.rates[i].dirty_rate = dirtyrate;
470         dirtyrate_sum += dirtyrate;
471     }
472 
473     DirtyStat.dirty_rate = dirtyrate_sum;
474     free(dirty_pages);
475 }
476 
477 static void calculate_dirtyrate_sample_vm(struct DirtyRateConfig config)
478 {
479     struct RamblockDirtyInfo *block_dinfo = NULL;
480     int block_count = 0;
481     int64_t msec = 0;
482     int64_t initial_time;
483 
484     rcu_read_lock();
485     initial_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
486     if (!record_ramblock_hash_info(&block_dinfo, config, &block_count)) {
487         goto out;
488     }
489     rcu_read_unlock();
490 
491     msec = config.sample_period_seconds * 1000;
492     msec = set_sample_page_period(msec, initial_time);
493     DirtyStat.start_time = initial_time / 1000;
494     DirtyStat.calc_time = msec / 1000;
495 
496     rcu_read_lock();
497     if (!compare_page_hash_info(block_dinfo, block_count)) {
498         goto out;
499     }
500 
501     update_dirtyrate(msec);
502 
503 out:
504     rcu_read_unlock();
505     free_ramblock_dirty_info(block_dinfo, block_count);
506 }
507 
508 static void calculate_dirtyrate(struct DirtyRateConfig config)
509 {
510     if (config.mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) {
511         calculate_dirtyrate_dirty_ring(config);
512     } else {
513         calculate_dirtyrate_sample_vm(config);
514     }
515 
516     trace_dirtyrate_calculate(DirtyStat.dirty_rate);
517 }
518 
519 void *get_dirtyrate_thread(void *arg)
520 {
521     struct DirtyRateConfig config = *(struct DirtyRateConfig *)arg;
522     int ret;
523     rcu_register_thread();
524 
525     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_UNSTARTED,
526                               DIRTY_RATE_STATUS_MEASURING);
527     if (ret == -1) {
528         error_report("change dirtyrate state failed.");
529         return NULL;
530     }
531 
532     calculate_dirtyrate(config);
533 
534     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_MEASURING,
535                               DIRTY_RATE_STATUS_MEASURED);
536     if (ret == -1) {
537         error_report("change dirtyrate state failed.");
538     }
539 
540     rcu_unregister_thread();
541     return NULL;
542 }
543 
544 void qmp_calc_dirty_rate(int64_t calc_time,
545                          bool has_sample_pages,
546                          int64_t sample_pages,
547                          bool has_mode,
548                          DirtyRateMeasureMode mode,
549                          Error **errp)
550 {
551     static struct DirtyRateConfig config;
552     QemuThread thread;
553     int ret;
554     int64_t start_time;
555 
556     /*
557      * If the dirty rate is already being measured, don't attempt to start.
558      */
559     if (qatomic_read(&CalculatingState) == DIRTY_RATE_STATUS_MEASURING) {
560         error_setg(errp, "the dirty rate is already being measured.");
561         return;
562     }
563 
564     if (!is_sample_period_valid(calc_time)) {
565         error_setg(errp, "calc-time is out of range[%d, %d].",
566                          MIN_FETCH_DIRTYRATE_TIME_SEC,
567                          MAX_FETCH_DIRTYRATE_TIME_SEC);
568         return;
569     }
570 
571     if (!has_mode) {
572         mode =  DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING;
573     }
574 
575     if (has_sample_pages && mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) {
576         error_setg(errp, "either sample-pages or dirty-ring can be specified.");
577         return;
578     }
579 
580     if (has_sample_pages) {
581         if (!is_sample_pages_valid(sample_pages)) {
582             error_setg(errp, "sample-pages is out of range[%d, %d].",
583                             MIN_SAMPLE_PAGE_COUNT,
584                             MAX_SAMPLE_PAGE_COUNT);
585             return;
586         }
587     } else {
588         sample_pages = DIRTYRATE_DEFAULT_SAMPLE_PAGES;
589     }
590 
591     /*
592      * dirty ring mode only works when kvm dirty ring is enabled.
593      */
594     if ((mode == DIRTY_RATE_MEASURE_MODE_DIRTY_RING) &&
595         !kvm_dirty_ring_enabled()) {
596         error_setg(errp, "dirty ring is disabled, use sample-pages method "
597                          "or remeasure later.");
598         return;
599     }
600 
601     /*
602      * Init calculation state as unstarted.
603      */
604     ret = dirtyrate_set_state(&CalculatingState, CalculatingState,
605                               DIRTY_RATE_STATUS_UNSTARTED);
606     if (ret == -1) {
607         error_setg(errp, "init dirty rate calculation state failed.");
608         return;
609     }
610 
611     config.sample_period_seconds = calc_time;
612     config.sample_pages_per_gigabytes = sample_pages;
613     config.mode = mode;
614 
615     cleanup_dirtyrate_stat(config);
616 
617     /*
618      * update dirty rate mode so that we can figure out what mode has
619      * been used in last calculation
620      **/
621     dirtyrate_mode = mode;
622 
623     start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
624     init_dirtyrate_stat(start_time, config);
625 
626     qemu_thread_create(&thread, "get_dirtyrate", get_dirtyrate_thread,
627                        (void *)&config, QEMU_THREAD_DETACHED);
628 }
629 
630 struct DirtyRateInfo *qmp_query_dirty_rate(Error **errp)
631 {
632     return query_dirty_rate_info();
633 }
634 
635 void hmp_info_dirty_rate(Monitor *mon, const QDict *qdict)
636 {
637     DirtyRateInfo *info = query_dirty_rate_info();
638 
639     monitor_printf(mon, "Status: %s\n",
640                    DirtyRateStatus_str(info->status));
641     monitor_printf(mon, "Start Time: %"PRIi64" (ms)\n",
642                    info->start_time);
643     monitor_printf(mon, "Sample Pages: %"PRIu64" (per GB)\n",
644                    info->sample_pages);
645     monitor_printf(mon, "Period: %"PRIi64" (sec)\n",
646                    info->calc_time);
647     monitor_printf(mon, "Mode: %s\n",
648                    DirtyRateMeasureMode_str(info->mode));
649     monitor_printf(mon, "Dirty rate: ");
650     if (info->has_dirty_rate) {
651         monitor_printf(mon, "%"PRIi64" (MB/s)\n", info->dirty_rate);
652         if (info->has_vcpu_dirty_rate) {
653             DirtyRateVcpuList *rate, *head = info->vcpu_dirty_rate;
654             for (rate = head; rate != NULL; rate = rate->next) {
655                 monitor_printf(mon, "vcpu[%"PRIi64"], Dirty rate: %"PRIi64
656                                " (MB/s)\n", rate->value->id,
657                                rate->value->dirty_rate);
658             }
659         }
660     } else {
661         monitor_printf(mon, "(not ready)\n");
662     }
663 
664     qapi_free_DirtyRateVcpuList(info->vcpu_dirty_rate);
665     g_free(info);
666 }
667 
668 void hmp_calc_dirty_rate(Monitor *mon, const QDict *qdict)
669 {
670     int64_t sec = qdict_get_try_int(qdict, "second", 0);
671     int64_t sample_pages = qdict_get_try_int(qdict, "sample_pages_per_GB", -1);
672     bool has_sample_pages = (sample_pages != -1);
673     bool dirty_ring = qdict_get_try_bool(qdict, "dirty_ring", false);
674     DirtyRateMeasureMode mode =
675         (dirty_ring ? DIRTY_RATE_MEASURE_MODE_DIRTY_RING :
676          DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING);
677     Error *err = NULL;
678 
679     if (!sec) {
680         monitor_printf(mon, "Incorrect period length specified!\n");
681         return;
682     }
683 
684     qmp_calc_dirty_rate(sec, has_sample_pages, sample_pages, true,
685                         mode, &err);
686     if (err) {
687         hmp_handle_error(mon, err);
688         return;
689     }
690 
691     monitor_printf(mon, "Starting dirty rate measurement with period %"PRIi64
692                    " seconds\n", sec);
693     monitor_printf(mon, "[Please use 'info dirty_rate' to check results]\n");
694 }
695