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[70.30.145.63]) by smtp.gmail.com with ESMTPSA id h18-20020a02c732000000b00363d6918540sm5997022jao.171.2023.02.15.11.59.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Feb 2023 11:59:02 -0800 (PST) Date: Wed, 15 Feb 2023 14:59:00 -0500 From: Peter Xu To: Juan Quintela Cc: qemu-devel@nongnu.org, Eric Blake , "Dr. David Alan Gilbert" , Yanan Wang , Marcel Apfelbaum , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Eduardo Habkost , Markus Armbruster Subject: Re: [PATCH v6 1/3] multifd: Create property multifd-flush-after-each-section Message-ID: References: <20230215180231.7644-1-quintela@redhat.com> <20230215180231.7644-2-quintela@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230215180231.7644-2-quintela@redhat.com> Received-SPF: pass client-ip=170.10.129.124; envelope-from=peterx@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, Feb 15, 2023 at 07:02:29PM +0100, Juan Quintela wrote: > We used to flush all channels at the end of each RAM section > sent. That is not needed, so preparing to only flush after a full > iteration through all the RAM. > > Default value of the property is false. But we return "true" in > migrate_multifd_flush_after_each_section() until we implement the code > in following patches. > > Signed-off-by: Juan Quintela This line can be dropped, after (I assume) git commit helped to add the other one below. :) Normally that's also why I put R-bs before my SoB because I should have two SoB but then I merge them into the last; git is happy with that too. > Reviewed-by: Dr. David Alan Gilbert > Signed-off-by: Juan Quintela Acked-by: Peter Xu But some nitpicks below (I'll leave those to you to decide whether to rework or keep them as is..). > > --- > > Rename each-iteration to after-each-section > Rename multifd-sync-after-each-section to > multifd-flush-after-each-section > --- > qapi/migration.json | 21 ++++++++++++++++++++- > migration/migration.h | 1 + > hw/core/machine.c | 1 + > migration/migration.c | 17 +++++++++++++++-- > 4 files changed, 37 insertions(+), 3 deletions(-) > > diff --git a/qapi/migration.json b/qapi/migration.json > index c84fa10e86..3afd81174d 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -478,6 +478,24 @@ > # should not affect the correctness of postcopy migration. > # (since 7.1) > # > +# @multifd-flush-after-each-section: flush every channel after each > +# section sent. This assures that > +# we can't mix pages from one > +# iteration through ram pages with > +# pages for the following > +# iteration. We really only need > +# to do this flush after we have go > +# through all the dirty pages. > +# For historical reasons, we do > +# that after each section. This is > +# suboptimal (we flush too many > +# times). > +# Default value is false. > +# Setting this capability has no > +# effect until the patch that > +# removes this comment. > +# (since 8.0) IMHO the core of this new "cap" is the new RAM_SAVE_FLAG_MULTIFD_FLUSH bit in the stream protocol, but it's not referenced here. I would suggest simplify the content but highlight the core change: @multifd-lazy-flush: When enabled, multifd will only do sync flush after each whole round of bitmap scan. Otherwise it'll be done per RAM save iteration (which happens with a much higher frequency). Please consider enable this as long as possible, and keep this off only if any of the src/dst QEMU binary doesn't support it. This capability is bound to the new RAM save flag RAM_SAVE_FLAG_MULTIFD_FLUSH, the new flag will only be used and recognized when this feature bit set. I know you dislike multifd-lazy-flush, but that's still the best I can come up with when writting this (yeah I still like it :-p), please bare with me and take whatever you think the best. > +# > # Features: > # @unstable: Members @x-colo and @x-ignore-shared are experimental. > # > @@ -492,7 +510,8 @@ > 'dirty-bitmaps', 'postcopy-blocktime', 'late-block-activate', > { 'name': 'x-ignore-shared', 'features': [ 'unstable' ] }, > 'validate-uuid', 'background-snapshot', > - 'zero-copy-send', 'postcopy-preempt'] } > + 'zero-copy-send', 'postcopy-preempt', > + 'multifd-flush-after-each-section'] } > > ## > # @MigrationCapabilityStatus: > diff --git a/migration/migration.h b/migration/migration.h > index 2da2f8a164..7f0f4260ba 100644 > --- a/migration/migration.h > +++ b/migration/migration.h > @@ -424,6 +424,7 @@ int migrate_multifd_channels(void); > MultiFDCompression migrate_multifd_compression(void); > int migrate_multifd_zlib_level(void); > int migrate_multifd_zstd_level(void); > +bool migrate_multifd_flush_after_each_section(void); > > #ifdef CONFIG_LINUX > bool migrate_use_zero_copy_send(void); > diff --git a/hw/core/machine.c b/hw/core/machine.c > index f73fc4c45c..602e775f34 100644 > --- a/hw/core/machine.c > +++ b/hw/core/machine.c > @@ -54,6 +54,7 @@ const size_t hw_compat_7_1_len = G_N_ELEMENTS(hw_compat_7_1); > GlobalProperty hw_compat_7_0[] = { > { "arm-gicv3-common", "force-8-bit-prio", "on" }, > { "nvme-ns", "eui64-default", "on"}, > + { "migration", "multifd-flush-after-each-section", "on"}, [same note to IRC: need to revert if rename, but otherwise don't bother] Thanks, > }; > const size_t hw_compat_7_0_len = G_N_ELEMENTS(hw_compat_7_0); > > diff --git a/migration/migration.c b/migration/migration.c > index 90fca70cb7..cfba0da005 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -167,7 +167,8 @@ INITIALIZE_MIGRATE_CAPS_SET(check_caps_background_snapshot, > MIGRATION_CAPABILITY_XBZRLE, > MIGRATION_CAPABILITY_X_COLO, > MIGRATION_CAPABILITY_VALIDATE_UUID, > - MIGRATION_CAPABILITY_ZERO_COPY_SEND); > + MIGRATION_CAPABILITY_ZERO_COPY_SEND, > + MIGRATION_CAPABILITY_MULTIFD_FLUSH_AFTER_EACH_SECTION); > > /* When we add fault tolerance, we could have several > migrations at once. For now we don't need to add > @@ -2701,6 +2702,17 @@ bool migrate_use_multifd(void) > return s->enabled_capabilities[MIGRATION_CAPABILITY_MULTIFD]; > } > > +bool migrate_multifd_flush_after_each_section(void) > +{ > + MigrationState *s = migrate_get_current(); > + > + /* > + * Until the patch that remove this comment, we always return that > + * the capability is enabled. > + */ > + return true || s->enabled_capabilities[MIGRATION_CAPABILITY_MULTIFD_FLUSH_AFTER_EACH_SECTION]; (I'd rather not care about what happens if someone applies only this patch not the latter two by dropping "true ||" directly here, but again, no a huge deal) > +} > + > bool migrate_pause_before_switchover(void) > { > MigrationState *s; > @@ -4535,7 +4547,8 @@ static Property migration_properties[] = { > DEFINE_PROP_MIG_CAP("x-zero-copy-send", > MIGRATION_CAPABILITY_ZERO_COPY_SEND), > #endif > - > + DEFINE_PROP_MIG_CAP("multifd-flush-after-each-section", > + MIGRATION_CAPABILITY_MULTIFD_FLUSH_AFTER_EACH_SECTION), > DEFINE_PROP_END_OF_LIST(), > }; > > -- > 2.39.1 > > -- Peter Xu