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Tue, 28 Apr 2020 14:51:18 +0000 (UTC) Received: from work-vm (ovpn-113-77.ams2.redhat.com [10.36.113.77]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B1B1B5D710; Tue, 28 Apr 2020 14:51:12 +0000 (UTC) Date: Tue, 28 Apr 2020 15:51:10 +0100 From: "Dr. David Alan Gilbert" To: Wei Wang Subject: Re: [PATCH v2] migration/xbzrle: add encoding rate Message-ID: <20200428145110.GH2794@work-vm> References: <1587974511-14953-1-git-send-email-wei.w.wang@intel.com> MIME-Version: 1.0 In-Reply-To: <1587974511-14953-1-git-send-email-wei.w.wang@intel.com> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/04/28 02:06:42 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kevin.tian@intel.com, berrange@redhat.com, quintela@redhat.com, qemu-devel@nongnu.org, peterx@redhat.com, gloryxiao@tencent.com, yi.y.sun@intel.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Wei Wang (wei.w.wang@intel.com) 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. >=20 > Signed-off-by: Yi Sun > Signed-off-by: Wei Wang > --- > migration/migration.c | 1 + > migration/ram.c | 38 ++++++++++++++++++++++++++++++++++++-- > monitor/hmp-cmds.c | 2 ++ > qapi/migration.json | 5 ++++- > 4 files changed, 43 insertions(+), 3 deletions(-) >=20 > ChangeLog: > - include the 3 bytes (ENCODING_FLAG_XBZRLE flag and encoded_len) when > calculating the encoding rate. Similar to the compress rate > calculation, the 8 byte RAM_SAVE_FLAG_CONTINUE flag isn't included in > the calculation. >=20 > diff --git a/migration/migration.c b/migration/migration.c > index 187ac04..e404213 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -930,6 +930,7 @@ static void populate_ram_info(MigrationInfo *info, Mi= grationState *s) > info->xbzrle_cache->pages =3D xbzrle_counters.pages; > info->xbzrle_cache->cache_miss =3D xbzrle_counters.cache_miss; > info->xbzrle_cache->cache_miss_rate =3D xbzrle_counters.cache_mi= ss_rate; > + info->xbzrle_cache->encoding_rate =3D xbzrle_counters.encoding_r= ate; > info->xbzrle_cache->overflow =3D xbzrle_counters.overflow; > } > =20 > diff --git a/migration/ram.c b/migration/ram.c > index 04f13fe..f46ab96 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 xbzrle encoded bytes since the beginning of the period = */ > + uint64_t xbzrle_bytes_prev; > =20 > /* 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; > } > =20 > + /* > + * 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 generat= es 2KB, > + * 2nd page turns out to be skipped (i.e. no new bytes written to th= e > + * page), the overall encoding rate will be 8KB / 2KB =3D 4, which h= as the > + * skipped page included. In this way, the encoding rate can tell if= the > + * guest page is good for xbzrle encoding. > + */ > + xbzrle_counters.pages++; Can you explain how that works with overflow? Doesn't overflow return -1 here, not increment the bytes, so it looks like you've xbzrle'd a page, but the encoding rate hasn't incremented. Dave > prev_cached_page =3D get_cached_data(XBZRLE.cache, current_addr); > =20 > /* save current buffer into memory */ > @@ -736,8 +752,12 @@ static int save_xbzrle_page(RAMState *rs, uint8_t **= current_data, > qemu_put_be16(rs->f, encoded_len); > qemu_put_buffer(rs->f, XBZRLE.encoded_buf, encoded_len); > bytes_xbzrle +=3D encoded_len + 1 + 2; > - xbzrle_counters.pages++; > - xbzrle_counters.bytes +=3D bytes_xbzrle; > + /* > + * Like compressed_size (please see update_compress_thread_counts), > + * the xbzrle encoded bytes don't count the 8 byte header with > + * RAM_SAVE_FLAG_CONTINUE. > + */ > + xbzrle_counters.bytes +=3D bytes_xbzrle - 8; > ram_counters.transferred +=3D bytes_xbzrle; > =20 > return 1; > @@ -870,9 +890,23 @@ static void migration_update_rates(RAMState *rs, int= 64_t end_time) > } > =20 > if (migrate_use_xbzrle()) { > + double encoded_size, unencoded_size; > + > xbzrle_counters.cache_miss_rate =3D (double)(xbzrle_counters.cac= he_miss - > rs->xbzrle_cache_miss_prev) / page_count; > rs->xbzrle_cache_miss_prev =3D xbzrle_counters.cache_miss; > + unencoded_size =3D (xbzrle_counters.pages - rs->xbzrle_pages_pre= v) * > + TARGET_PAGE_SIZE; > + encoded_size =3D xbzrle_counters.bytes - rs->xbzrle_bytes_prev; > + if (xbzrle_counters.pages =3D=3D rs->xbzrle_pages_prev) { > + xbzrle_counters.encoding_rate =3D 0; > + } else if (!encoded_size) { > + xbzrle_counters.encoding_rate =3D UINT64_MAX; > + } else { > + xbzrle_counters.encoding_rate =3D unencoded_size / encoded_s= ize; > + } > + rs->xbzrle_pages_prev =3D xbzrle_counters.pages; > + rs->xbzrle_bytes_prev =3D xbzrle_counters.bytes; > } > =20 > if (migrate_use_compression()) { > diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c > index 9b94e67..c2a3a66 100644 > --- a/monitor/hmp-cmds.c > +++ b/monitor/hmp-cmds.c > @@ -303,6 +303,8 @@ void hmp_info_migrate(Monitor *mon, const QDict *qdic= t) > 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 eca2981..358e402 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 encoded bytes (since 5.1) > +# > # @overflow: number of overflows > # > # Since: 1.2 > @@ -77,7 +79,7 @@ > { 'struct': 'XBZRLECacheStats', > 'data': {'cache-size': 'int', 'bytes': 'int', 'pages': 'int', > 'cache-miss': 'int', 'cache-miss-rate': 'number', > - 'overflow': 'int' } } > + 'encoding-rate': 'number', 'overflow': 'int' } } > =20 > ## > # @CompressionStats: > @@ -337,6 +339,7 @@ > # "pages":2444343, > # "cache-miss":2244, > # "cache-miss-rate":0.123, > +# "encoding-rate":80.1, > # "overflow":34434 > # } > # } > --=20 > 1.8.3.1 >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK