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[84.125.73.40]) by smtp.gmail.com with ESMTPSA id o20-20020a1c7514000000b0039c4ec6fdacsm19219263wmc.40.2022.06.21.14.03.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Jun 2022 14:03:54 -0700 (PDT) From: Juan Quintela To: Peter Xu Cc: qemu-devel@nongnu.org, Leonardo Bras Soares Passos , "Daniel P . Berrange" , "Dr . David Alan Gilbert" , Manish Mishra Subject: Re: [PATCH v7 01/14] migration: Add postcopy-preempt capability In-Reply-To: <20220524221151.18225-2-peterx@redhat.com> (Peter Xu's message of "Tue, 24 May 2022 18:11:38 -0400") References: <20220524221151.18225-1-peterx@redhat.com> <20220524221151.18225-2-peterx@redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) Date: Tue, 21 Jun 2022 23:03:53 +0200 Message-ID: <87v8stvidi.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=170.10.133.124; envelope-from=quintela@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Peter Xu wrote: > Firstly, postcopy already preempts precopy due to the fact that we do > unqueue_page() first before looking into dirty bits. > > However that's not enough, e.g., when there're host huge page enabled, when > sending a precopy huge page, a postcopy request needs to wait until the whole > huge page that is sending to finish. That could introduce quite some delay, > the bigger the huge page is the larger delay it'll bring. > > This patch adds a new capability to allow postcopy requests to preempt existing > precopy page during sending a huge page, so that postcopy requests can be > serviced even faster. > > Meanwhile to send it even faster, bypass the precopy stream by providing a > standalone postcopy socket for sending requested pages. > > Since the new behavior will not be compatible with the old behavior, this will > not be the default, it's enabled only when the new capability is set on both > src/dst QEMUs. > > This patch only adds the capability itself, the logic will be added in follow > up patches. > > Reviewed-by: Dr. David Alan Gilbert > Signed-off-by: Peter Xu > --- > migration/migration.c | 23 +++++++++++++++++++++++ > migration/migration.h | 1 + > qapi/migration.json | 8 +++++++- > 3 files changed, 31 insertions(+), 1 deletion(-) > > diff --git a/migration/migration.c b/migration/migration.c > index 31739b2af9..f15e1593ac 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -1240,6 +1240,11 @@ static bool migrate_caps_check(bool *cap_list, > error_setg(errp, "Postcopy is not compatible with ignore-shared"); > return false; > } > + > + if (cap_list[MIGRATION_CAPABILITY_MULTIFD]) { > + error_setg(errp, "Multifd is not supported in postcopy"); > + return false; > + } > } Multifd is supported with postcopy. We just switch to old precopy when we switch to postcopy. I am dropping that chunk. For the rest: Reviewed-by: Juan Quintela > > if (cap_list[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]) { > @@ -1283,6 +1288,13 @@ static bool migrate_caps_check(bool *cap_list, > return false; > } > > + if (cap_list[MIGRATION_CAPABILITY_POSTCOPY_PREEMPT]) { > + if (!cap_list[MIGRATION_CAPABILITY_POSTCOPY_RAM]) { > + error_setg(errp, "Postcopy preempt requires postcopy-ram"); > + return false; > + } > + } > + > return true; > } > > @@ -2669,6 +2681,15 @@ bool migrate_background_snapshot(void) > return s->enabled_capabilities[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]; > } > > +bool migrate_postcopy_preempt(void) > +{ > + MigrationState *s; > + > + s = migrate_get_current(); > + > + return s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_PREEMPT]; > +} > + > /* migration thread support */ > /* > * Something bad happened to the RP stream, mark an error > @@ -4283,6 +4304,8 @@ static Property migration_properties[] = { > DEFINE_PROP_MIG_CAP("x-compress", MIGRATION_CAPABILITY_COMPRESS), > DEFINE_PROP_MIG_CAP("x-events", MIGRATION_CAPABILITY_EVENTS), > DEFINE_PROP_MIG_CAP("x-postcopy-ram", MIGRATION_CAPABILITY_POSTCOPY_RAM), > + DEFINE_PROP_MIG_CAP("x-postcopy-preempt", > + MIGRATION_CAPABILITY_POSTCOPY_PREEMPT), > DEFINE_PROP_MIG_CAP("x-colo", MIGRATION_CAPABILITY_X_COLO), > DEFINE_PROP_MIG_CAP("x-release-ram", MIGRATION_CAPABILITY_RELEASE_RAM), > DEFINE_PROP_MIG_CAP("x-block", MIGRATION_CAPABILITY_BLOCK), > diff --git a/migration/migration.h b/migration/migration.h > index 485d58b95f..d2269c826c 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -400,6 +400,7 @@ int migrate_decompress_threads(void); > bool migrate_use_events(void); > bool migrate_postcopy_blocktime(void); > bool migrate_background_snapshot(void); > +bool migrate_postcopy_preempt(void); > > /* Sending on the return path - generic and then for each message type */ > void migrate_send_rp_shut(MigrationIncomingState *mis, > diff --git a/qapi/migration.json b/qapi/migration.json > index 6130cd9fae..d8c3810ba2 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -461,6 +461,12 @@ > # procedure starts. The VM RAM is saved with running VM. > # (since 6.0) > # > +# @postcopy-preempt: If enabled, the migration process will allow postcopy > +# requests to preempt precopy stream, so postcopy requests > +# will be handled faster. This is a performance feature and > +# should not affect the correctness of postcopy migration. > +# (since 7.1) > +# > # Features: > # @unstable: Members @x-colo and @x-ignore-shared are experimental. > # > @@ -474,7 +480,7 @@ > 'block', 'return-path', 'pause-before-switchover', 'multifd', > 'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate', > { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] }, > - 'validate-uuid', 'background-snapshot'] } > + 'validate-uuid', 'background-snapshot', 'postcopy-preempt'] } > > ## > # @MigrationCapabilityStatus: