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Mon, 4 May 2020 09:08:59 +0000 (UTC) Date: Mon, 4 May 2020 10:08:55 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: "Dr. David Alan Gilbert" Subject: Re: [RFC patch v1 2/3] qemu-file: add buffered mode Message-ID: <20200504090855.GA115875@redhat.com> References: <1586776334-641239-1-git-send-email-dplotnikov@virtuozzo.com> <1586776334-641239-3-git-send-email-dplotnikov@virtuozzo.com> <20200427121433.GI2923@work-vm> MIME-Version: 1.0 In-Reply-To: <20200427121433.GI2923@work-vm> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.120; envelope-from=berrange@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/04 05:09:11 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 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, FROM_EXCESS_BASE64=0.979, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: den@openvz.org, Denis Plotnikov , qemu-devel@nongnu.org, quintela@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Apr 27, 2020 at 01:14:33PM +0100, Dr. David Alan Gilbert wrote: > * Denis Plotnikov (dplotnikov@virtuozzo.com) wrote: > > The patch adds ability to qemu-file to write the data > > asynchronously to improve the performance on writing. > > Before, only synchronous writing was supported. > >=20 > > Enabling of the asyncronous mode is managed by new > > "enabled_buffered" callback. >=20 > It's a bit invasive isn't it - changes a lot of functions in a lot of > places! > The multifd code separated the control headers from the data on separate > fd's - but that doesn't help your case. >=20 > Is there any chance you could do this by using the existing 'save_page' > hook (that RDMA uses). >=20 > In the cover letter you mention direct qemu_fflush calls - have we got a > few too many in some palces that you think we can clean out? When I first introduced the QIOChannel framework, I hoped that we could largely eliminate QEMUFile as a concept. Thus I'm a bit suspicious of the idea of introducing more functionality to QEMUFile, especially as the notion of buffering I/O is rather generic. Is there scope for having a QIOChannelBuffered object for doing buffering. Would that provide better isolation from the migration code and thus be less invasive/complex to maintain ? Regards, Daniel --=20 |: 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= :|