Re: [PATCH v2 2/4] migration/calc-dirty-rate: detailed stats in sampling mode

["Wang, Lei" <lei4.wang@intel.com>]

On 4/27/2023 20:42, Andrei Gudkov via wrote:
> Collect number of dirty pages for progresseively increasing time
> periods starting with 125ms up to number of seconds specified with
> calc-dirty-rate. Report through qmp and hmp: 1) vector of dirty page
> measurements, 2) page size, 3) total number of VM pages, 4) number
> of sampled pages.
> 
> Signed-off-by: Andrei Gudkov <gudkov.andrei@huawei.com>
> ---
>  migration/dirtyrate.c | 165 +++++++++++++++++++++++++++++-------------
>  migration/dirtyrate.h |  25 ++++++-
>  qapi/migration.json   |  24 +++++-
>  3 files changed, 160 insertions(+), 54 deletions(-)
> 
> diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
> index acba3213a3..4491bbe91a 100644
> --- a/migration/dirtyrate.c
> +++ b/migration/dirtyrate.c
> @@ -224,6 +224,7 @@ static struct DirtyRateInfo *query_dirty_rate_info(void)
>      info->calc_time = DirtyStat.calc_time;
>      info->sample_pages = DirtyStat.sample_pages;
>      info->mode = dirtyrate_mode;
> +    info->page_size = TARGET_PAGE_SIZE;
>  
>      if (qatomic_read(&CalculatingState) == DIRTY_RATE_STATUS_MEASURED) {
>          info->has_dirty_rate = true;
> @@ -245,6 +246,29 @@ static struct DirtyRateInfo *query_dirty_rate_info(void)
>              info->vcpu_dirty_rate = head;
>          }
>  
> +        if (dirtyrate_mode == DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING) {
> +            int64List *periods_head = NULL;
> +            int64List **periods_tail = &periods_head;
> +            int64List *n_dirty_pages_head = NULL;
> +            int64List **n_dirty_pages_tail = &n_dirty_pages_head;
> +
> +            info->n_total_pages = DirtyStat.page_sampling.n_total_pages;
> +            info->has_n_total_pages = true;
> +
> +            info->n_sampled_pages = DirtyStat.page_sampling.n_sampled_pages;
> +            info->has_n_sampled_pages = true;
> +
> +            for (i = 0; i < DirtyStat.page_sampling.n_readings; i++) {
> +                DirtyReading *dr = &DirtyStat.page_sampling.readings[i];
> +                QAPI_LIST_APPEND(periods_tail, dr->period);
> +                QAPI_LIST_APPEND(n_dirty_pages_tail, dr->n_dirty_pages);
> +            }
> +            info->n_dirty_pages = n_dirty_pages_head;
> +            info->periods = periods_head;
> +            info->has_n_dirty_pages = true;
> +            info->has_periods = true;
> +        }
> +
>          if (dirtyrate_mode == DIRTY_RATE_MEASURE_MODE_DIRTY_BITMAP) {
>              info->sample_pages = 0;
>          }
> @@ -265,9 +289,11 @@ static void init_dirtyrate_stat(int64_t start_time,
>  
>      switch (config.mode) {
>      case DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING:
> -        DirtyStat.page_sampling.total_dirty_samples = 0;
> -        DirtyStat.page_sampling.total_sample_count = 0;
> -        DirtyStat.page_sampling.total_block_mem_MB = 0;
> +        DirtyStat.page_sampling.n_total_pages = 0;
> +        DirtyStat.page_sampling.n_sampled_pages = 0;
> +        DirtyStat.page_sampling.n_readings = 0;
> +        DirtyStat.page_sampling.readings = g_try_malloc0_n(MAX_DIRTY_READINGS,
> +                                                          sizeof(DirtyReading));
>          break;
>      case DIRTY_RATE_MEASURE_MODE_DIRTY_RING:
>          DirtyStat.dirty_ring.nvcpu = -1;
> @@ -285,28 +311,10 @@ static void cleanup_dirtyrate_stat(struct DirtyRateConfig config)
>          free(DirtyStat.dirty_ring.rates);
>          DirtyStat.dirty_ring.rates = NULL;
>      }
> -}
> -
> -static void update_dirtyrate_stat(struct RamblockDirtyInfo *info)
> -{
> -    DirtyStat.page_sampling.total_dirty_samples += info->sample_dirty_count;
> -    DirtyStat.page_sampling.total_sample_count += info->sample_pages_count;
> -    /* size of total pages in MB */
> -    DirtyStat.page_sampling.total_block_mem_MB += (info->ramblock_pages *
> -                                                   TARGET_PAGE_SIZE) >> 20;
> -}
> -
> -static void update_dirtyrate(uint64_t msec)
> -{
> -    uint64_t dirtyrate;
> -    uint64_t total_dirty_samples = DirtyStat.page_sampling.total_dirty_samples;
> -    uint64_t total_sample_count = DirtyStat.page_sampling.total_sample_count;
> -    uint64_t total_block_mem_MB = DirtyStat.page_sampling.total_block_mem_MB;
> -
> -    dirtyrate = total_dirty_samples * total_block_mem_MB *
> -                1000 / (total_sample_count * msec);
> -
> -    DirtyStat.dirty_rate = dirtyrate;
> +    if (DirtyStat.page_sampling.readings) {
> +        free(DirtyStat.page_sampling.readings);
> +        DirtyStat.page_sampling.readings = NULL;
> +    }
>  }
>  
>  /*
> @@ -377,12 +385,14 @@ static bool save_ramblock_hash(struct RamblockDirtyInfo *info)
>          return false;
>      }
>  
> -    rand  = g_rand_new();
> +    rand = g_rand_new();
> +    DirtyStat.page_sampling.n_total_pages += info->ramblock_pages;
>      for (i = 0; i < sample_pages_count; i++) {
>          info->sample_page_vfn[i] = g_rand_int_range(rand, 0,
>                                                      info->ramblock_pages - 1);
>          info->hash_result[i] = get_ramblock_vfn_hash(info,
>                                                       info->sample_page_vfn[i]);
> +        DirtyStat.page_sampling.n_sampled_pages++;

How about:
	
DirtyStat.page_sampling.n_sampled_pages += sample_pages_count;

out of the loop to avoid doing the calculation multiple times?

>      }
>      g_rand_free(rand);
>  
> @@ -479,18 +489,20 @@ out:
>      return ret;
>  }
>  
> -static void calc_page_dirty_rate(struct RamblockDirtyInfo *info)
> +static int64_t calc_page_dirty_rate(struct RamblockDirtyInfo *info)
>  {
>      uint32_t hash;
>      int i;
>  
> +    int64_t n_dirty = 0;
>      for (i = 0; i < info->sample_pages_count; i++) {
>          hash = get_ramblock_vfn_hash(info, info->sample_page_vfn[i]);
>          if (hash != info->hash_result[i]) {
> +            n_dirty++;
>              trace_calc_page_dirty_rate(info->idstr, hash, info->hash_result[i]);
> -            info->sample_dirty_count++;
>          }
>      }
> +    return n_dirty;
>  }
>  
>  static struct RamblockDirtyInfo *
> @@ -519,11 +531,12 @@ find_block_matched(RAMBlock *block, int count,
>      return &infos[i];
>  }
>  
> -static bool compare_page_hash_info(struct RamblockDirtyInfo *info,
> +static int64_t compare_page_hash_info(struct RamblockDirtyInfo *info,
>                                    int block_count)
>  {
>      struct RamblockDirtyInfo *block_dinfo = NULL;
>      RAMBlock *block = NULL;
> +    int64_t n_dirty = 0;
>  
>      RAMBLOCK_FOREACH_MIGRATABLE(block) {
>          if (skip_sample_ramblock(block)) {
> @@ -533,15 +546,10 @@ static bool compare_page_hash_info(struct RamblockDirtyInfo *info,
>          if (block_dinfo == NULL) {
>              continue;
>          }
> -        calc_page_dirty_rate(block_dinfo);
> -        update_dirtyrate_stat(block_dinfo);
> -    }
> -
> -    if (DirtyStat.page_sampling.total_sample_count == 0) {
> -        return false;
> +        n_dirty += calc_page_dirty_rate(block_dinfo);
>      }
>  
> -    return true;
> +    return n_dirty;
>  }
>  
>  static inline void record_dirtypages_bitmap(DirtyPageRecord *dirty_pages,
> @@ -642,34 +650,77 @@ static void calculate_dirtyrate_dirty_ring(struct DirtyRateConfig config)
>      DirtyStat.dirty_rate = dirtyrate_sum;
>  }
>  
> +static int64_t increase_period(int64_t prev_period, int64_t max_period)
> +{
> +    int64_t delta;
> +    int64_t next_period;
> +
> +    if (prev_period < 500) {
> +        delta = 125;
> +    } else if (prev_period < 1000) {
> +        delta = 250;
> +    } else if (prev_period < 2000) {
> +        delta = 500;
> +    } else if (prev_period < 4000) {
> +        delta = 1000;
> +    } else if (prev_period < 10000) {
> +        delta = 2000;
> +    } else {
> +        delta = 5000;
> +    }
> +
> +    next_period = prev_period + delta;
> +    if (next_period + delta >= max_period) {
> +        next_period = max_period;
> +    }
> +    return next_period;
> +}
> +
> +
>  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;
> +    int64_t current_time;
>  
> +    /* initial pass */
>      rcu_read_lock();
>      initial_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> -    if (!record_ramblock_hash_info(&block_dinfo, config, &block_count)) {
> +    bool ok = record_ramblock_hash_info(&block_dinfo, config, &block_count);
> +    rcu_read_unlock();
> +    if ((!ok) || (DirtyStat.page_sampling.n_sampled_pages == 0)) {
>          goto out;
>      }
> -    rcu_read_unlock();
>  
> -    msec = config.sample_period_seconds * 1000;
> -    msec = dirty_stat_wait(msec, initial_time);
> -    DirtyStat.start_time = initial_time / 1000;
> -    DirtyStat.calc_time = msec / 1000;
> +    int64_t period = INITIAL_PERIOD_MS;
> +    while (true) {
> +        current_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> +        int64_t delta = initial_time + period - current_time;
> +        if (delta > 0) {
> +            g_usleep(delta * 1000);
> +        }
>  
> -    rcu_read_lock();
> -    if (!compare_page_hash_info(block_dinfo, block_count)) {
> -        goto out;
> -    }
> +        rcu_read_lock();
> +        current_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> +        int64_t n_dirty = compare_page_hash_info(block_dinfo, block_count);
> +        rcu_read_unlock();
>  
> -    update_dirtyrate(msec);
> +        SampleVMStat *ps = &DirtyStat.page_sampling;
> +        ps->readings[ps->n_readings].period = current_time - initial_time;
> +        ps->readings[ps->n_readings].n_dirty_pages = n_dirty;
> +        ps->n_readings++;
> +
> +        if (period >= DirtyStat.calc_time * 1000) {
> +            int64_t mb_total = (ps->n_total_pages * TARGET_PAGE_SIZE) >> 20;
> +            int64_t mb_dirty = n_dirty * mb_total / ps->n_sampled_pages;
> +            DirtyStat.dirty_rate = mb_dirty * 1000 / period;
> +            break;
> +        }
> +        period = increase_period(period, DirtyStat.calc_time * 1000);
> +    }
>  
>  out:
> -    rcu_read_unlock();
>      free_ramblock_dirty_info(block_dinfo, block_count);
>  }
>  
> @@ -836,7 +887,23 @@ void hmp_info_dirty_rate(Monitor *mon, const QDict *qdict)
>          monitor_printf(mon, "(not ready)\n");
>      }
>  
> +    if (info->has_n_total_pages) {
> +        monitor_printf(mon, "Page count (page size %d):\n", TARGET_PAGE_SIZE);
> +        monitor_printf(mon, " Total: %"PRIi64"\n", info->n_total_pages);
> +        monitor_printf(mon, "  Sampled: %"PRIi64"\n", info->n_sampled_pages);
> +        int64List *periods = info->periods;
> +        int64List *n_dirty_pages = info->n_dirty_pages;
> +        while (periods) {
> +            monitor_printf(mon, "   Dirty(%"PRIi64"ms): %"PRIi64"\n",
> +                           periods->value, n_dirty_pages->value);
> +            periods = periods->next;
> +            n_dirty_pages = n_dirty_pages->next;
> +        }
> +    }
> +
>      qapi_free_DirtyRateVcpuList(info->vcpu_dirty_rate);
> +    qapi_free_int64List(info->periods);
> +    qapi_free_int64List(info->n_dirty_pages);
>      g_free(info);
>  }
>  
> diff --git a/migration/dirtyrate.h b/migration/dirtyrate.h
> index 594a5c0bb6..7a97e2b076 100644
> --- a/migration/dirtyrate.h
> +++ b/migration/dirtyrate.h
> @@ -42,6 +42,18 @@
>  #define MIN_SAMPLE_PAGE_COUNT                     128
>  #define MAX_SAMPLE_PAGE_COUNT                     16384
>  
> +/*
> + * Initial sampling period expressed in milliseconds
> + */
> +#define INITIAL_PERIOD_MS 125
> +
> +/*
> + * Upper bound on the number of DirtyReadings calculcated based on

Nit: calculcated -> calculated

> + * INITIAL_PERIOD_MS, MAX_FETCH_DIRTYRATE_TIME_SEC and increase_period()
> + */
> +#define MAX_DIRTY_READINGS 32
> +
> +
>  struct DirtyRateConfig {
>      uint64_t sample_pages_per_gigabytes; /* sample pages per GB */
>      int64_t sample_period_seconds; /* time duration between two sampling */
> @@ -57,14 +69,19 @@ struct RamblockDirtyInfo {
>      uint64_t ramblock_pages; /* ramblock size in TARGET_PAGE_SIZE */
>      uint64_t *sample_page_vfn; /* relative offset address for sampled page */
>      uint64_t sample_pages_count; /* count of sampled pages */
> -    uint64_t sample_dirty_count; /* count of dirty pages we measure */
>      uint32_t *hash_result; /* array of hash result for sampled pages */
>  };
>  
> +typedef struct DirtyReading {
> +    int64_t period; /* time period in milliseconds */
> +    int64_t n_dirty_pages; /* number of observed dirty pages */
> +} DirtyReading;
> +
>  typedef struct SampleVMStat {
> -    uint64_t total_dirty_samples; /* total dirty sampled page */
> -    uint64_t total_sample_count; /* total sampled pages */
> -    uint64_t total_block_mem_MB; /* size of total sampled pages in MB */
> +    int64_t n_total_pages; /* total number of pages */
> +    int64_t n_sampled_pages; /* number of sampled pages */
> +    int64_t n_readings;
> +    DirtyReading *readings;
>  } SampleVMStat;
>  
>  /*
> diff --git a/qapi/migration.json b/qapi/migration.json
> index 2c35b7b9cf..f818f51e0e 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -1805,6 +1805,22 @@
>  # @vcpu-dirty-rate: dirtyrate for each vcpu if dirty-ring
>  #                   mode specified (Since 6.2)
>  #
> +# @page-size: page size in bytes (since 8.1)
> +#
> +# @n-total-pages: [page-sampling] total number of VM pages (since 8.1)
> +#
> +# @n-sampled-pages: [page-sampling] number of sampled VM pages (since 8.1)
> +#
> +# @periods: [page-sampling] array of time periods expressed in milliseconds
> +#           for which dirty-sample measurements were collected (since 8.1)
> +#
> +# @n-dirty-pages: [page-sampling] number of pages among all sampled pages
> +#                 that were observed as changed during respective time period.
> +#                 i-th element of this array corresponds to the i-th element
> +#                 of the @periods array, i.e. @n-dirty-pages[i] is the number
> +#                 of dirtied pages during period of @periods[i] milliseconds
> +#                 after the initiation of calc-dirty-rate (since 8.1)
> +#
>  # Since: 5.2
>  ##
>  { 'struct': 'DirtyRateInfo',
> @@ -1814,7 +1830,13 @@
>             'calc-time': 'int64',
>             'sample-pages': 'uint64',
>             'mode': 'DirtyRateMeasureMode',
> -           '*vcpu-dirty-rate': [ 'DirtyRateVcpu' ] } }
> +           '*vcpu-dirty-rate': [ 'DirtyRateVcpu' ],
> +           'page-size': 'int64',
> +           '*n-total-pages': 'int64',
> +           '*n-sampled-pages': 'int64',
> +           '*periods': ['int64'],
> +           '*n-dirty-pages': ['int64'] } }
> +
>  
>  ##
>  # @calc-dirty-rate: