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[82.30.61.225]) by smtp.gmail.com with ESMTPSA id bq12-20020a5d5a0c000000b0021d54a16344sm6351852wrb.92.2022.07.04.04.40.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 Jul 2022 04:40:11 -0700 (PDT) Date: Mon, 4 Jul 2022 12:40:09 +0100 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Cc: Markus Armbruster , Leonardo Bras , Juan Quintela , Eric Blake , Peter Xu , qemu-devel@nongnu.org Subject: Re: [PATCH v2 2/3] Add zero-copy-copied migration stat Message-ID: References: <20220701155935.482503-1-leobras@redhat.com> <20220701155935.482503-3-leobras@redhat.com> <877d4tz9gx.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/2.2.6 (2022-06-05) 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: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 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_NONE=-0.0001, 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Daniel P. Berrangé (berrange@redhat.com) wrote: > On Mon, Jul 04, 2022 at 08:18:54AM +0200, Markus Armbruster wrote: > > Leonardo Bras writes: > > > > > Signed-off-by: Leonardo Bras > > > --- > > > qapi/migration.json | 5 ++++- > > > migration/migration.c | 1 + > > > monitor/hmp-cmds.c | 4 ++++ > > > 3 files changed, 9 insertions(+), 1 deletion(-) > > > > > > diff --git a/qapi/migration.json b/qapi/migration.json > > > index 7102e474a6..925f009868 100644 > > > --- a/qapi/migration.json > > > +++ b/qapi/migration.json > > > @@ -55,6 +55,9 @@ > > > # @postcopy-bytes: The number of bytes sent during the post-copy phase > > > # (since 7.0). > > > # > > > +# @zero-copy-copied: The number of zero-copy flushes that reported data sent > > > +# using zero-copy that ended up being copied. (since 7.2) > > > > The description feels awkward. What's a "zero-copy flush", and why > > should the user care? I figure what users care about is the number of > > all-zero pages we had to "copy", i.e. send the bulky way. Is this what > > @zero-copy-copied reports? > > MigrationCapability field @zero-copy-send instructs QEMU to try to > avoid copying data between userspace and kernel space when transmitting > RAM region. > > Even if the kernel supports zero copy, it is not guaranteed to happen, > it is merely a request to try. > > QEMU periodically (once per migration iteration) flushes outstanding > zero-copy requests and gets an indication back of whether any copies > took place or not. > > So this counter is a reflection of how many iterations resulted in > zero-copy not being fully honoured. > > IOW, ideally this counter will always be zero. If it is non-zero, > then the magnitude gives a very very very rough guide to what's > going on. If it is '1' then it was just a transient limitation. > If it matches the number of migration iterations, then it is a > more systemic limitation. > > Incidentally, do we report the migration iteration count ? I > thought we did, but i'm not finding it now that I look. Yes we do; it's dirty-sync-count Dave > > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK