Re: [PATCH v1 2/2] migration/xbzrle: add encoding rate

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Apr 20, 2020 at 11:06:43AM +0800, Wei Wang wrote:
> Users may need to check the xbzrle encoding rate to know if the guest
> memory is xbzrle encoding-friendly, and dynamically turn off the
> encoding if the encoding rate is low.
> 
> Signed-off-by: Yi Sun <yi.y.sun@intel.com>
> Signed-off-by: Wei Wang <wei.w.wang@intel.com>
> ---
>  migration/migration.c |  1 +
>  migration/ram.c       | 31 +++++++++++++++++++++++++++++--
>  monitor/hmp-cmds.c    |  2 ++
>  qapi/migration.json   |  5 ++++-
>  slirp                 |  2 +-
>  5 files changed, 37 insertions(+), 4 deletions(-)
> 
> diff --git a/migration/migration.c b/migration/migration.c
> index 8e7ee0d76b..84a556a4ac 100644
> --- a/migration/migration.c
> +++ b/migration/migration.c
> @@ -930,6 +930,7 @@ static void populate_ram_info(MigrationInfo *info, MigrationState *s)
>          info->xbzrle_cache->pages = xbzrle_counters.pages;
>          info->xbzrle_cache->cache_miss = xbzrle_counters.cache_miss;
>          info->xbzrle_cache->cache_miss_rate = xbzrle_counters.cache_miss_rate;
> +        info->xbzrle_cache->encoding_rate = xbzrle_counters.encoding_rate;
>          info->xbzrle_cache->overflow = xbzrle_counters.overflow;
>      }
>  
> diff --git a/migration/ram.c b/migration/ram.c
> index bca5878f25..c87c38ec80 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -327,6 +327,10 @@ struct RAMState {
>      uint64_t num_dirty_pages_period;
>      /* xbzrle misses since the beginning of the period */
>      uint64_t xbzrle_cache_miss_prev;
> +    /* Amount of xbzrle pages since the beginning of the period */
> +    uint64_t xbzrle_pages_prev;
> +    /* Amount of encoded bytes since the beginning of the period */
> +    uint64_t encoded_size_prev;
>  
>      /* compression statistics since the beginning of the period */
>      /* amount of count that no free thread to compress data */
> @@ -696,6 +700,18 @@ static int save_xbzrle_page(RAMState *rs, uint8_t **current_data,
>          return -1;
>      }
>  
> +    /*
> +     * Reaching here means the page has hit the xbzrle cache, no matter what
> +     * encoding result it is (normal encoding, overflow or skipping the page),
> +     * count the page as encoded. This is used to caculate the encoding rate.
> +     *
> +     * Example: 2 pages (8KB) being encoded, first page encoding generates 2KB,
> +     * 2nd page turns out to be skipped (i.e. no new bytes written to the
> +     * page), the overall encoding rate will be 8KB / 2KB = 4, which has the
> +     * skipped page included. In this way, the encoding rate can tell if the
> +     * guest page is good for xbzrle encoding.
> +     */
> +    xbzrle_counters.pages++;
>      prev_cached_page = get_cached_data(XBZRLE.cache, current_addr);
>  
>      /* save current buffer into memory */
> @@ -736,7 +752,6 @@ static int save_xbzrle_page(RAMState *rs, uint8_t **current_data,
>      qemu_put_be16(rs->f, encoded_size);
>      qemu_put_buffer(rs->f, XBZRLE.encoded_buf, encoded_size);
>      bytes_xbzrle += encoded_size + 1 + 2;
> -    xbzrle_counters.pages++;
>      xbzrle_counters.encoded_size += encoded_size;
>      ram_counters.transferred += bytes_xbzrle;
>  
> @@ -859,7 +874,7 @@ uint64_t ram_get_total_transferred_pages(void)
>  static void migration_update_rates(RAMState *rs, int64_t end_time)
>  {
>      uint64_t page_count = rs->target_page_count - rs->target_page_count_prev;
> -    double compressed_size;
> +    double compressed_size, encoded_size, unencoded_size;
>  
>      /* calculate period counters */
>      ram_counters.dirty_pages_rate = rs->num_dirty_pages_period * 1000
> @@ -873,6 +888,18 @@ static void migration_update_rates(RAMState *rs, int64_t end_time)
>          xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss -
>              rs->xbzrle_cache_miss_prev) / page_count;
>          rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss;
> +        unencoded_size = (xbzrle_counters.pages - rs->xbzrle_pages_prev) *
> +                         TARGET_PAGE_SIZE;
> +        encoded_size = xbzrle_counters.encoded_size - rs->encoded_size_prev;
> +        if (xbzrle_counters.pages == rs->xbzrle_pages_prev) {
> +            xbzrle_counters.encoding_rate = 0;
> +        } else if (!encoded_size) {
> +            xbzrle_counters.encoding_rate = UINT64_MAX;
> +        } else {
> +            xbzrle_counters.encoding_rate = unencoded_size / encoded_size;
> +        }
> +        rs->xbzrle_pages_prev = xbzrle_counters.pages;
> +        rs->encoded_size_prev = xbzrle_counters.encoded_size;
>      }
>  
>      if (migrate_use_compression()) {
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index 6d3b35ca64..07f41e582f 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -303,6 +303,8 @@ void hmp_info_migrate(Monitor *mon, const QDict *qdict)
>                         info->xbzrle_cache->cache_miss);
>          monitor_printf(mon, "xbzrle cache miss rate: %0.2f\n",
>                         info->xbzrle_cache->cache_miss_rate);
> +        monitor_printf(mon, "xbzrle encoding rate: %0.2f\n",
> +                       info->xbzrle_cache->encoding_rate);
>          monitor_printf(mon, "xbzrle overflow: %" PRIu64 "\n",
>                         info->xbzrle_cache->overflow);
>      }
> diff --git a/qapi/migration.json b/qapi/migration.json
> index bf195ff6ac..ee4513c565 100644
> --- a/qapi/migration.json
> +++ b/qapi/migration.json
> @@ -70,6 +70,8 @@
>  #
>  # @cache-miss-rate: rate of cache miss (since 2.1)
>  #
> +# @encoding-rate: rate of cache miss
> +#
>  # @overflow: number of overflows
>  #
>  # Since: 1.2
> @@ -77,7 +79,7 @@
>  { 'struct': 'XBZRLECacheStats',
>    'data': {'cache-size': 'int', 'encoded_size': 'int', 'pages': 'int',
>             'cache-miss': 'int', 'cache-miss-rate': 'number',
> -           'overflow': 'int' } }
> +           'encoding-rate': 'number', 'overflow': 'int' } }
>  
>  ##
>  # @CompressionStats:
> @@ -337,6 +339,7 @@
>  #             "pages":2444343,
>  #             "cache-miss":2244,
>  #             "cache-miss-rate":0.123,
> +#             "encoding-rate":80.1,
>  #             "overflow":34434
>  #          }
>  #       }
> diff --git a/slirp b/slirp
> index 55ab21c9a3..126c04acba 160000
> --- a/slirp
> +++ b/slirp
> @@ -1 +1 @@
> -Subproject commit 55ab21c9a36852915b81f1b41ebaf3b6509dd8ba
> +Subproject commit 126c04acbabd7ad32c2b018fe10dfac2a3bc1210

Accidental inclusion of submodule changes

Regards,
Daniel
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