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[82.132.239.190]) by smtp.gmail.com with ESMTPSA id a9sm8983126wmm.32.2022.02.03.07.46.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Feb 2022 07:46:21 -0800 (PST) Date: Thu, 3 Feb 2022 15:46:19 +0000 From: "Dr. David Alan Gilbert" To: Peter Xu Subject: Re: [PATCH RFC 13/15] migration: Add postcopy-preempt capability Message-ID: References: <20220119080929.39485-1-peterx@redhat.com> <20220119080929.39485-14-peterx@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220119080929.39485-14-peterx@redhat.com> User-Agent: Mutt/2.1.5 (2021-12-30) Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=dgilbert@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=-0.086, 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: , Cc: Juan Quintela , qemu-devel@nongnu.org, Leonardo Bras Soares Passos Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Xu (peterx@redhat.com) 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. > > Signed-off-by: Peter Xu Reviewed-by: Dr. David Alan Gilbert > --- > 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 15a48b548a..84a8fbd80d 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -1227,6 +1227,11 @@ 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; > + } > } > > if (cap_list[MIGRATION_CAPABILITY_BACKGROUND_SNAPSHOT]) { > @@ -1270,6 +1275,13 @@ 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; > } > > @@ -2623,6 +2635,15 @@ 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 > @@ -4239,6 +4260,8 @@ 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 d0c0902ec9..9d39ccfcf5 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -391,6 +391,7 @@ 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 bbfd48cf0b..f00b365bd5 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -452,6 +452,12 @@ > # 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 7.0) > +# > # Features: > # @unstable: Members @x-colo and @x-ignore-shared are experimental. > # > @@ -465,7 +471,7 @@ > '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: > -- > 2.32.0 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK