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[79.181.55.232]) by smtp.gmail.com with ESMTPSA id q1sm3255091wmc.15.2020.06.09.08.37.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Jun 2020 08:37:58 -0700 (PDT) Date: Tue, 9 Jun 2020 11:37:56 -0400 From: "Michael S. Tsirkin" To: Cornelia Huck Subject: Re: [PATCH v4 1/5] virtio-pci: add virtio_pci_optimal_num_queues() helper Message-ID: <20200609113745-mutt-send-email-mst@kernel.org> References: <20200527102925.128013-1-stefanha@redhat.com> <20200527102925.128013-2-stefanha@redhat.com> <20200528173555.5f079b70.cohuck@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200528173555.5f079b70.cohuck@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.120; envelope-from=mst@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/09 02:44:16 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-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: , Cc: Kevin Wolf , Pankaj Gupta , Eduardo Habkost , qemu-block@nongnu.org, qemu-devel@nongnu.org, Max Reitz , Stefan Hajnoczi , Paolo Bonzini , Fam Zheng , Raphael Norwitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, May 28, 2020 at 05:35:55PM +0200, Cornelia Huck wrote: > On Wed, 27 May 2020 11:29:21 +0100 > Stefan Hajnoczi wrote: > > > Multi-queue devices achieve the best performance when each vCPU has a > > dedicated queue. This ensures that virtqueue used notifications are > > handled on the same vCPU that submitted virtqueue buffers. When another > > vCPU handles the the notification an IPI will be necessary to wake the > > submission vCPU and this incurs a performance overhead. > > > > Provide a helper function that virtio-pci devices will use in later > > patches to automatically select the optimal number of queues. > > > > Signed-off-by: Stefan Hajnoczi > > --- > > hw/virtio/virtio-pci.h | 9 +++++++++ > > hw/virtio/virtio-pci.c | 7 +++++++ > > 2 files changed, 16 insertions(+) > > That looks like a good idea, since the policy can be easily tweaked in > one place later. > > For ccw, I don't see a good way to arrive at an optimal number of > queues. Is there something we should do for mmio? If yes, should this > be a callback in VirtioBusClass? Stefan do you plan to address this?