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Wed, 18 Sep 2024 05:53:00 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.192.47]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3F4783001FEF; Wed, 18 Sep 2024 05:52:59 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id C9C2F21E6A28; Wed, 18 Sep 2024 07:52:56 +0200 (CEST) From: Markus Armbruster To: dave@treblig.org Cc: peterx@redhat.com, farosas@suse.de, eblake@redhat.com, armbru@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH 2/3] migration: Remove unused zero-blocks capability In-Reply-To: <20240918000207.182683-3-dave@treblig.org> (dave@treblig.org's message of "Wed, 18 Sep 2024 01:02:06 +0100") References: <20240918000207.182683-1-dave@treblig.org> <20240918000207.182683-3-dave@treblig.org> Date: Wed, 18 Sep 2024 07:52:56 +0200 Message-ID: <87msk54ifb.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@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_H3=0.001, RCVD_IN_MSPIKE_WL=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 dave@treblig.org writes: > From: "Dr. David Alan Gilbert" > > migrate_zero_blocks is unused since > eef0bae3a7 ("migration: Remove block migration") > > Remove it. > That whole zero-blocks capability was just for old-school > block migration anyway. > > Remove the capability as well. > > Signed-off-by: Dr. David Alan Gilbert > --- > migration/options.c | 8 -------- > migration/options.h | 1 - > qapi/migration.json | 10 +--------- > 3 files changed, 1 insertion(+), 18 deletions(-) > > diff --git a/migration/options.c b/migration/options.c > index 9460c5dee9..997e060612 100644 > --- a/migration/options.c > +++ b/migration/options.c > @@ -177,7 +177,6 @@ Property migration_properties[] = { > DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE), > DEFINE_PROP_MIG_CAP("x-rdma-pin-all", MIGRATION_CAPABILITY_RDMA_PIN_ALL), > DEFINE_PROP_MIG_CAP("x-auto-converge", MIGRATION_CAPABILITY_AUTO_CONVERGE), > - DEFINE_PROP_MIG_CAP("x-zero-blocks", MIGRATION_CAPABILITY_ZERO_BLOCKS), > 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", Property of (pseudo-)device "migration". The "x-" prefix suggests we expect management software not to rely on it. Okay. [...] > diff --git a/qapi/migration.json b/qapi/migration.json > index b66cccf107..82d0fc962e 100644 > --- a/qapi/migration.json > +++ b/qapi/migration.json > @@ -389,13 +389,6 @@ > # footprint is mlock()'d on demand or all at once. Refer to > # docs/rdma.txt for usage. Disabled by default. (since 2.0) > # > -# @zero-blocks: During storage migration encode blocks of zeroes > -# efficiently. This essentially saves 1MB of zeroes per block on > -# the wire. Enabling requires source and target VM to support > -# this feature. To enable it is sufficient to enable the > -# capability on the source VM. The feature is disabled by > -# default. (since 1.6) > -# > # @events: generate events for each migration state change (since 2.4) > # > # @auto-converge: If enabled, QEMU will automatically throttle down > @@ -483,7 +476,7 @@ > # Since: 1.2 > ## > { 'enum': 'MigrationCapability', > - 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', 'zero-blocks', > + 'data': ['xbzrle', 'rdma-pin-all', 'auto-converge', > 'events', 'postcopy-ram', > { 'name': 'x-colo', 'features': [ 'unstable' ] }, > 'release-ram', This is used by migrate-set-capabilities and query-migrate-capabilities, via ['MigrationCapabilityStatus']. query-migrate-capabilities is unaffected: it couldn't return zero-blocks anymore even before the patch. migrate-set-capabilities changes incompatibly, I'm afraid. Before the patch: {"execute": "migrate-set-capabilities", "arguments": {"capabilities": [{"capability": "zero-blocks", "state": true}]}} {"return": {}} Afterwards: {"error": {"class": "GenericError", "desc": "Parameter 'capability' does not accept value 'zero-blocks'"}} If we had somehow rejected the capability when it made no sense, removing it now it never makes sense would be obviously fine. The straight & narrow path is to deprecate now, remove later. If we believe nothing relies on it, we can bend the rules and remove right away. Missing then: update to docs/about/removed-features.rst. > @@ -542,7 +535,6 @@ > # {"state": false, "capability": "xbzrle"}, > # {"state": false, "capability": "rdma-pin-all"}, > # {"state": false, "capability": "auto-converge"}, > -# {"state": false, "capability": "zero-blocks"}, > # {"state": true, "capability": "events"}, > # {"state": false, "capability": "postcopy-ram"}, > # {"state": false, "capability": "x-colo"} Example for query-migrate-capabilities. Good.