From 34a68001f16208a574cbef0cd2d4e2d681faa604 Mon Sep 17 00:00:00 2001 From: Andrei Gudkov Date: Tue, 5 Sep 2023 10:05:43 +0300 Subject: [PATCH 1/2] migration/calc-dirty-rate: millisecond-granularity period This patch allows to measure dirty page rate for sub-second intervals of time. An optional argument is introduced -- calc-time-unit. For example: {"execute": "calc-dirty-rate", "arguments": {"calc-time": 500, "calc-time-unit": "millisecond"} } Millisecond granularity allows to make predictions whether migration will succeed or not. To do this, calculate dirty rate with calc-time set to max allowed downtime (e.g. 300ms), convert measured rate into volume of dirtied memory, and divide by network throughput. If the value is lower than max allowed downtime, then migration will converge. Measurement results for single thread randomly writing to a 1/4/24GiB memory region: +----------------+-----------------------------------------------+ | calc-time | dirty rate MiB/s | | (milliseconds) +----------------+---------------+--------------+ | | theoretical | page-sampling | dirty-bitmap | | | (at 3M wr/sec) | | | +----------------+----------------+---------------+--------------+ | 1GiB | +----------------+----------------+---------------+--------------+ | 100 | 6996 | 7100 | 3192 | | 200 | 4606 | 4660 | 2655 | | 300 | 3305 | 3280 | 2371 | | 400 | 2534 | 2525 | 2154 | | 500 | 2041 | 2044 | 1871 | | 750 | 1365 | 1341 | 1358 | | 1000 | 1024 | 1052 | 1025 | | 1500 | 683 | 678 | 684 | | 2000 | 512 | 507 | 513 | +----------------+----------------+---------------+--------------+ | 4GiB | +----------------+----------------+---------------+--------------+ | 100 | 10232 | 8880 | 4070 | | 200 | 8954 | 8049 | 3195 | | 300 | 7889 | 7193 | 2881 | | 400 | 6996 | 6530 | 2700 | | 500 | 6245 | 5772 | 2312 | | 750 | 4829 | 4586 | 2465 | | 1000 | 3865 | 3780 | 2178 | | 1500 | 2694 | 2633 | 2004 | | 2000 | 2041 | 2031 | 1789 | +----------------+----------------+---------------+--------------+ | 24GiB | +----------------+----------------+---------------+--------------+ | 100 | 11495 | 8640 | 5597 | | 200 | 11226 | 8616 | 3527 | | 300 | 10965 | 8386 | 2355 | | 400 | 10713 | 8370 | 2179 | | 500 | 10469 | 8196 | 2098 | | 750 | 9890 | 7885 | 2556 | | 1000 | 9354 | 7506 | 2084 | | 1500 | 8397 | 6944 | 2075 | | 2000 | 7574 | 6402 | 2062 | +----------------+----------------+---------------+--------------+ Theoretical values are computed according to the following formula: size * (1 - (1-(4096/size))^(time*wps)) / (time * 2^20), where size is in bytes, time is in seconds, and wps is number of writes per second. Signed-off-by: Andrei Gudkov Reviewed-by: Hyman Huang Message-Id: Signed-off-by: Hyman Huang --- migration/dirtyrate.c | 107 +++++++++++++++++++++++++++++------------- migration/dirtyrate.h | 12 +++-- qapi/migration.json | 58 ++++++++++++++++++----- 3 files changed, 128 insertions(+), 49 deletions(-) diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c index bccb3515e3..a461b28bb5 100644 --- a/migration/dirtyrate.c +++ b/migration/dirtyrate.c @@ -189,10 +189,9 @@ retry: return duration; } -static bool is_sample_period_valid(int64_t sec) +static bool is_calc_time_valid(int64_t msec) { - if (sec < MIN_FETCH_DIRTYRATE_TIME_SEC || - sec > MAX_FETCH_DIRTYRATE_TIME_SEC) { + if ((msec < MIN_CALC_TIME_MS) || (msec > MAX_CALC_TIME_MS)) { return false; } @@ -216,7 +215,39 @@ static int dirtyrate_set_state(int *state, int old_state, int new_state) } } -static struct DirtyRateInfo *query_dirty_rate_info(void) +/* Decimal power of given time unit relative to one second */ +static int time_unit_to_power(TimeUnit time_unit) +{ + switch (time_unit) { + case TIME_UNIT_SECOND: + return 0; + case TIME_UNIT_MILLISECOND: + return -3; + default: + assert(false); /* unreachable */ + return 0; + } +} + +static int64_t convert_time_unit(int64_t value, TimeUnit unit_from, + TimeUnit unit_to) +{ + int power = time_unit_to_power(unit_from) - + time_unit_to_power(unit_to); + while (power < 0) { + value /= 10; + power += 1; + } + while (power > 0) { + value *= 10; + power -= 1; + } + return value; +} + + +static struct DirtyRateInfo * +query_dirty_rate_info(TimeUnit calc_time_unit) { int i; int64_t dirty_rate = DirtyStat.dirty_rate; @@ -225,7 +256,10 @@ static struct DirtyRateInfo *query_dirty_rate_info(void) info->status = CalculatingState; info->start_time = DirtyStat.start_time; - info->calc_time = DirtyStat.calc_time; + info->calc_time = convert_time_unit(DirtyStat.calc_time_ms, + TIME_UNIT_MILLISECOND, + calc_time_unit); + info->calc_time_unit = calc_time_unit; info->sample_pages = DirtyStat.sample_pages; info->mode = dirtyrate_mode; @@ -264,7 +298,7 @@ static void init_dirtyrate_stat(int64_t start_time, { DirtyStat.dirty_rate = -1; DirtyStat.start_time = start_time; - DirtyStat.calc_time = config.sample_period_seconds; + DirtyStat.calc_time_ms = config.calc_time_ms; DirtyStat.sample_pages = config.sample_pages_per_gigabytes; switch (config.mode) { @@ -574,7 +608,6 @@ static inline void dirtyrate_manual_reset_protect(void) static void calculate_dirtyrate_dirty_bitmap(struct DirtyRateConfig config) { - int64_t msec = 0; int64_t start_time; DirtyPageRecord dirty_pages; @@ -602,9 +635,7 @@ static void calculate_dirtyrate_dirty_bitmap(struct DirtyRateConfig config) start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); DirtyStat.start_time = start_time / 1000; - msec = config.sample_period_seconds * 1000; - msec = dirty_stat_wait(msec, start_time); - DirtyStat.calc_time = msec / 1000; + DirtyStat.calc_time_ms = dirty_stat_wait(config.calc_time_ms, start_time); /* * do two things. @@ -615,12 +646,12 @@ static void calculate_dirtyrate_dirty_bitmap(struct DirtyRateConfig config) record_dirtypages_bitmap(&dirty_pages, false); - DirtyStat.dirty_rate = do_calculate_dirtyrate(dirty_pages, msec); + DirtyStat.dirty_rate = do_calculate_dirtyrate(dirty_pages, + DirtyStat.calc_time_ms); } static void calculate_dirtyrate_dirty_ring(struct DirtyRateConfig config) { - int64_t duration; uint64_t dirtyrate = 0; uint64_t dirtyrate_sum = 0; int i = 0; @@ -631,12 +662,10 @@ static void calculate_dirtyrate_dirty_ring(struct DirtyRateConfig config) DirtyStat.start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000; /* calculate vcpu dirtyrate */ - duration = vcpu_calculate_dirtyrate(config.sample_period_seconds * 1000, - &DirtyStat.dirty_ring, - GLOBAL_DIRTY_DIRTY_RATE, - true); - - DirtyStat.calc_time = duration / 1000; + DirtyStat.calc_time_ms = vcpu_calculate_dirtyrate(config.calc_time_ms, + &DirtyStat.dirty_ring, + GLOBAL_DIRTY_DIRTY_RATE, + true); /* calculate vm dirtyrate */ for (i = 0; i < DirtyStat.dirty_ring.nvcpu; i++) { @@ -652,7 +681,6 @@ static void calculate_dirtyrate_sample_vm(struct DirtyRateConfig config) { struct RamblockDirtyInfo *block_dinfo = NULL; int block_count = 0; - int64_t msec = 0; int64_t initial_time; rcu_read_lock(); @@ -662,17 +690,16 @@ static void calculate_dirtyrate_sample_vm(struct DirtyRateConfig config) } rcu_read_unlock(); - msec = config.sample_period_seconds * 1000; - msec = dirty_stat_wait(msec, initial_time); + DirtyStat.calc_time_ms = dirty_stat_wait(config.calc_time_ms, + initial_time); DirtyStat.start_time = initial_time / 1000; - DirtyStat.calc_time = msec / 1000; rcu_read_lock(); if (!compare_page_hash_info(block_dinfo, block_count)) { goto out; } - update_dirtyrate(msec); + update_dirtyrate(DirtyStat.calc_time_ms); out: rcu_read_unlock(); @@ -718,6 +745,8 @@ void *get_dirtyrate_thread(void *arg) } void qmp_calc_dirty_rate(int64_t calc_time, + bool has_calc_time_unit, + TimeUnit calc_time_unit, bool has_sample_pages, int64_t sample_pages, bool has_mode, @@ -737,10 +766,15 @@ void qmp_calc_dirty_rate(int64_t calc_time, return; } - if (!is_sample_period_valid(calc_time)) { - error_setg(errp, "calc-time is out of range[%d, %d].", - MIN_FETCH_DIRTYRATE_TIME_SEC, - MAX_FETCH_DIRTYRATE_TIME_SEC); + int64_t calc_time_ms = convert_time_unit( + calc_time, + has_calc_time_unit ? calc_time_unit : TIME_UNIT_SECOND, + TIME_UNIT_MILLISECOND + ); + + if (!is_calc_time_valid(calc_time_ms)) { + error_setg(errp, "Calculation time is out of range [%dms, %dms].", + MIN_CALC_TIME_MS, MAX_CALC_TIME_MS); return; } @@ -787,7 +821,7 @@ void qmp_calc_dirty_rate(int64_t calc_time, return; } - config.sample_period_seconds = calc_time; + config.calc_time_ms = calc_time_ms; config.sample_pages_per_gigabytes = sample_pages; config.mode = mode; @@ -806,14 +840,18 @@ void qmp_calc_dirty_rate(int64_t calc_time, (void *)&config, QEMU_THREAD_DETACHED); } -struct DirtyRateInfo *qmp_query_dirty_rate(Error **errp) + +struct DirtyRateInfo *qmp_query_dirty_rate(bool has_calc_time_unit, + TimeUnit calc_time_unit, + Error **errp) { - return query_dirty_rate_info(); + return query_dirty_rate_info( + has_calc_time_unit ? calc_time_unit : TIME_UNIT_SECOND); } void hmp_info_dirty_rate(Monitor *mon, const QDict *qdict) { - DirtyRateInfo *info = query_dirty_rate_info(); + DirtyRateInfo *info = query_dirty_rate_info(TIME_UNIT_SECOND); monitor_printf(mon, "Status: %s\n", DirtyRateStatus_str(info->status)); @@ -873,8 +911,11 @@ void hmp_calc_dirty_rate(Monitor *mon, const QDict *qdict) mode = DIRTY_RATE_MEASURE_MODE_DIRTY_RING; } - qmp_calc_dirty_rate(sec, has_sample_pages, sample_pages, true, - mode, &err); + qmp_calc_dirty_rate(sec, /* calc-time */ + false, TIME_UNIT_SECOND, /* calc-time-unit */ + has_sample_pages, sample_pages, + true, mode, + &err); if (err) { hmp_handle_error(mon, err); return; diff --git a/migration/dirtyrate.h b/migration/dirtyrate.h index 594a5c0bb6..869c060941 100644 --- a/migration/dirtyrate.h +++ b/migration/dirtyrate.h @@ -31,10 +31,12 @@ #define MIN_RAMBLOCK_SIZE 128 /* - * Take 1s as minimum time for calculation duration + * Allowed range for dirty page rate calculation (in milliseconds). + * Lower limit relates to the smallest realistic downtime it + * makes sense to impose on migration. */ -#define MIN_FETCH_DIRTYRATE_TIME_SEC 1 -#define MAX_FETCH_DIRTYRATE_TIME_SEC 60 +#define MIN_CALC_TIME_MS 50 +#define MAX_CALC_TIME_MS 60000 /* * Take 1/16 pages in 1G as the maxmum sample page count @@ -44,7 +46,7 @@ struct DirtyRateConfig { uint64_t sample_pages_per_gigabytes; /* sample pages per GB */ - int64_t sample_period_seconds; /* time duration between two sampling */ + int64_t calc_time_ms; /* desired calculation time (in milliseconds) */ DirtyRateMeasureMode mode; /* mode of dirtyrate measurement */ }; @@ -73,7 +75,7 @@ typedef struct SampleVMStat { struct DirtyRateStat { int64_t dirty_rate; /* dirty rate in MB/s */ int64_t start_time; /* calculation start time in units of second */ - int64_t calc_time; /* time duration of two sampling in units of second */ + int64_t calc_time_ms; /* actual calculation time (in milliseconds) */ uint64_t sample_pages; /* sample pages per GB */ union { SampleVMStat page_sampling; diff --git a/qapi/migration.json b/qapi/migration.json index 8843e74b59..1717aa4bbd 100644 --- a/qapi/migration.json +++ b/qapi/migration.json @@ -1836,6 +1836,21 @@ { 'enum': 'DirtyRateMeasureMode', 'data': ['page-sampling', 'dirty-ring', 'dirty-bitmap'] } +## +# @TimeUnit: +# +# Specifies unit in which time-related value is specified. +# +# @second: value is in seconds +# +# @millisecond: value is in milliseconds +# +# Since 8.2 +# +## +{ 'enum': 'TimeUnit', + 'data': ['second', 'millisecond'] } + ## # @DirtyRateInfo: # @@ -1848,8 +1863,10 @@ # # @start-time: start time in units of second for calculation # -# @calc-time: time period for which dirty page rate was measured -# (in seconds) +# @calc-time: time period for which dirty page rate was measured, +# expressed and rounded down to @calc-time-unit. +# +# @calc-time-unit: time unit of @calc-time (Since 8.2) # # @sample-pages: number of sampled pages per GiB of guest memory. # Valid only in page-sampling mode (Since 6.1) @@ -1866,6 +1883,7 @@ 'status': 'DirtyRateStatus', 'start-time': 'int64', 'calc-time': 'int64', + 'calc-time-unit': 'TimeUnit', 'sample-pages': 'uint64', 'mode': 'DirtyRateMeasureMode', '*vcpu-dirty-rate': [ 'DirtyRateVcpu' ] } } @@ -1901,12 +1919,16 @@ # This mode tracks page modification per each vCPU separately. It # requires that KVM accelerator property "dirty-ring-size" is set. # -# @calc-time: time period in units of second for which dirty page rate -# is calculated. Note that larger @calc-time values will -# typically result in smaller dirty page rates because page -# dirtying is a one-time event. Once some page is counted as -# dirty during @calc-time period, further writes to this page will -# not increase dirty page rate anymore. +# @calc-time: time period for which dirty page rate is calculated. +# By default it is specified in seconds, but the unit can be set +# explicitly with @calc-time-unit. Note that larger @calc-time +# values will typically result in smaller dirty page rates because +# page dirtying is a one-time event. Once some page is counted +# as dirty during @calc-time period, further writes to this page +# will not increase dirty page rate anymore. +# +# @calc-time-unit: time unit in which @calc-time is specified. +# By default it is seconds. (Since 8.2) # # @sample-pages: number of sampled pages per each GiB of guest memory. # Default value is 512. For 4KiB guest pages this corresponds to @@ -1924,8 +1946,16 @@ # -> {"execute": "calc-dirty-rate", "arguments": {"calc-time": 1, # 'sample-pages': 512} } # <- { "return": {} } +# +# Measure dirty rate using dirty bitmap for 500 milliseconds: +# +# -> {"execute": "calc-dirty-rate", "arguments": {"calc-time": 500, +# "calc-time-unit": "millisecond", "mode": "dirty-bitmap"} } +# +# <- { "return": {} } ## { 'command': 'calc-dirty-rate', 'data': {'calc-time': 'int64', + '*calc-time-unit': 'TimeUnit', '*sample-pages': 'int', '*mode': 'DirtyRateMeasureMode'} } @@ -1934,6 +1964,9 @@ # # Query results of the most recent invocation of @calc-dirty-rate. # +# @calc-time-unit: time unit in which to report calculation time. +# By default it is reported in seconds. (Since 8.2) +# # Since: 5.2 # # Examples: @@ -1941,14 +1974,17 @@ # 1. Measurement is in progress: # # <- {"status": "measuring", "sample-pages": 512, -# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10} +# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10, +# "calc-time-unit": "second"} # # 2. Measurement has been completed: # # <- {"status": "measured", "sample-pages": 512, "dirty-rate": 108, -# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10} +# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10, +# "calc-time-unit": "second"} ## -{ 'command': 'query-dirty-rate', 'returns': 'DirtyRateInfo' } +{ 'command': 'query-dirty-rate', 'data': {'*calc-time-unit': 'TimeUnit' }, + 'returns': 'DirtyRateInfo' } ## # @DirtyLimitInfo: From 320a6ccc769dc09ae7ad0b4838e322018f334bf4 Mon Sep 17 00:00:00 2001 From: Andrei Gudkov Date: Tue, 5 Sep 2023 12:18:39 +0300 Subject: [PATCH 2/2] migration/dirtyrate: use QEMU_CLOCK_HOST to report start-time Currently query-dirty-rate uses QEMU_CLOCK_REALTIME as the source for start-time field. This translates to clock_gettime(CLOCK_MONOTONIC), i.e. number of seconds since host boot. This is not very useful. The only reasonable use case of start-time I can imagine is to check whether previously completed measurements are too old or not. But this makes sense only if start-time is reported as host wall-clock time. This patch replaces source of start-time from QEMU_CLOCK_REALTIME to QEMU_CLOCK_HOST. Signed-off-by: Andrei Gudkov Reviewed-by: Hyman Huang Message-Id: <399861531e3b24a1ecea2ba453fb2c3d129fb03a.1693905328.git.gudkov.andrei@huawei.com> Signed-off-by: Hyman Huang --- migration/dirtyrate.c | 15 ++++++--------- qapi/migration.json | 4 ++-- 2 files changed, 8 insertions(+), 11 deletions(-) diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c index a461b28bb5..036ac017fc 100644 --- a/migration/dirtyrate.c +++ b/migration/dirtyrate.c @@ -293,11 +293,10 @@ query_dirty_rate_info(TimeUnit calc_time_unit) return info; } -static void init_dirtyrate_stat(int64_t start_time, - struct DirtyRateConfig config) +static void init_dirtyrate_stat(struct DirtyRateConfig config) { DirtyStat.dirty_rate = -1; - DirtyStat.start_time = start_time; + DirtyStat.start_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) / 1000; DirtyStat.calc_time_ms = config.calc_time_ms; DirtyStat.sample_pages = config.sample_pages_per_gigabytes; @@ -633,7 +632,7 @@ static void calculate_dirtyrate_dirty_bitmap(struct DirtyRateConfig config) record_dirtypages_bitmap(&dirty_pages, true); start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); - DirtyStat.start_time = start_time / 1000; + DirtyStat.start_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) / 1000; DirtyStat.calc_time_ms = dirty_stat_wait(config.calc_time_ms, start_time); @@ -659,7 +658,7 @@ static void calculate_dirtyrate_dirty_ring(struct DirtyRateConfig config) /* start log sync */ global_dirty_log_change(GLOBAL_DIRTY_DIRTY_RATE, true); - DirtyStat.start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000; + DirtyStat.start_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) / 1000; /* calculate vcpu dirtyrate */ DirtyStat.calc_time_ms = vcpu_calculate_dirtyrate(config.calc_time_ms, @@ -685,6 +684,7 @@ static void calculate_dirtyrate_sample_vm(struct DirtyRateConfig config) rcu_read_lock(); initial_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME); + DirtyStat.start_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) / 1000; if (!record_ramblock_hash_info(&block_dinfo, config, &block_count)) { goto out; } @@ -692,7 +692,6 @@ static void calculate_dirtyrate_sample_vm(struct DirtyRateConfig config) DirtyStat.calc_time_ms = dirty_stat_wait(config.calc_time_ms, initial_time); - DirtyStat.start_time = initial_time / 1000; rcu_read_lock(); if (!compare_page_hash_info(block_dinfo, block_count)) { @@ -756,7 +755,6 @@ void qmp_calc_dirty_rate(int64_t calc_time, static struct DirtyRateConfig config; QemuThread thread; int ret; - int64_t start_time; /* * If the dirty rate is already being measured, don't attempt to start. @@ -833,8 +831,7 @@ void qmp_calc_dirty_rate(int64_t calc_time, **/ dirtyrate_mode = mode; - start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000; - init_dirtyrate_stat(start_time, config); + init_dirtyrate_stat(config); qemu_thread_create(&thread, "get_dirtyrate", get_dirtyrate_thread, (void *)&config, QEMU_THREAD_DETACHED); diff --git a/qapi/migration.json b/qapi/migration.json index 1717aa4bbd..d8f3bbd7b0 100644 --- a/qapi/migration.json +++ b/qapi/migration.json @@ -1974,13 +1974,13 @@ # 1. Measurement is in progress: # # <- {"status": "measuring", "sample-pages": 512, -# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10, +# "mode": "page-sampling", "start-time": 1693900454, "calc-time": 10, # "calc-time-unit": "second"} # # 2. Measurement has been completed: # # <- {"status": "measured", "sample-pages": 512, "dirty-rate": 108, -# "mode": "page-sampling", "start-time": 3665220, "calc-time": 10, +# "mode": "page-sampling", "start-time": 1693900454, "calc-time": 10, # "calc-time-unit": "second"} ## { 'command': 'query-dirty-rate', 'data': {'*calc-time-unit': 'TimeUnit' },