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[79.176.159.122]) by smtp.gmail.com with ESMTPSA id u11sm11262234wrw.14.2021.05.24.02.38.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 24 May 2021 02:38:09 -0700 (PDT) Date: Mon, 24 May 2021 05:38:05 -0400 From: "Michael S. Tsirkin" To: Eugenio =?iso-8859-1?Q?P=E9rez?= Subject: Re: [RFC v3 00/29] vDPA software assisted live migration Message-ID: <20210524053144-mutt-send-email-mst@kernel.org> References: <20210519162903.1172366-1-eperezma@redhat.com> MIME-Version: 1.0 In-Reply-To: <20210519162903.1172366-1-eperezma@redhat.com> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: Parav Pandit , Markus Armbruster , qemu-devel@nongnu.org, Harpreet Singh Anand , Xiao W Wang , Stefan Hajnoczi , Eli Cohen , virtualization@lists.linux-foundation.org, Eric Blake , Michael Lilja X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Wed, May 19, 2021 at 06:28:34PM +0200, Eugenio P=E9rez wrote: > Commit 17 introduces the buffer forwarding. Previous one are for > preparations again, and laters are for enabling some obvious > optimizations. However, it needs the vdpa device to be able to map > every IOVA space, and some vDPA devices are not able to do so. Checking > of this is added in previous commits. That might become a significant limitation. And it worries me that this is such a big patchset which might yet take a while to get finalized. I have an idea: how about as a first step we implement a transparent switch from vdpa to a software virtio in QEMU or a software vhost in kernel? This will give us live migration quickly with performance comparable to failover but without dependance on guest cooperation. Next step could be driving vdpa from userspace while still copying packets to a pre-registered buffer. Finally your approach will be a performance optimization for devices that support arbitrary IOVA. Thoughts? -- = MST _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization