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[213.175.37.10]) by smtp.gmail.com with ESMTPSA id x11sm18322736wmg.46.2020.01.27.01.59.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Jan 2020 01:59:44 -0800 (PST) Date: Mon, 27 Jan 2020 10:59:42 +0100 From: Stefano Garzarella To: Stefan Hajnoczi Subject: Re: [PATCH v2 0/4] virtio-pci: enable blk and scsi multi-queue by default Message-ID: <20200127095942.4n4ikvfptirqhn7c@steredhat> References: <20200124100159.736209-1-stefanha@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200124100159.736209-1-stefanha@redhat.com> X-MC-Unique: xfr_27pAPv256gWtpjBtrw-1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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 , Fam Zheng , Eduardo Habkost , qemu-block@nongnu.org, "Michael S. Tsirkin" , cohuck@redhat.com, qemu-devel@nongnu.org, Max Reitz , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jan 24, 2020 at 10:01:55AM +0000, Stefan Hajnoczi wrote: > v2: > * Let the virtio-DEVICE-pci device select num-queues because the optimal > multi-queue configuration may differ between virtio-pci, virtio-mmio, = and > virtio-ccw [Cornelia] >=20 > Enabling multi-queue on virtio-pci storage devices improves performance o= n SMP > guests because the completion interrupt is handled on the vCPU that submi= tted > the I/O request. This avoids IPIs inside the guest. >=20 > Note that performance is unchanged in these cases: > 1. Uniprocessor guests. They don't have IPIs. > 2. Application threads might be scheduled on the sole vCPU that handles > completion interrupts purely by chance. (This is one reason why bench= mark > results can vary noticably between runs.) > 3. Users may bind the application to the vCPU that handles completion > interrupts. >=20 > Set the number of queues to the number of vCPUs by default. Older machin= e > types continue to default to 1 queue for live migration compatibility. >=20 > This patch improves IOPS by 1-4% on an Intel Optane SSD with 4 vCPUs, -dr= ive > aio=3Dnative, and fio bs=3D4k direct=3D1 rw=3Drandread. >=20 > Stefan Hajnoczi (4): > virtio-scsi: introduce a constant for fixed virtqueues > virtio-scsi: default num_queues to -smp N > virtio-blk: default num_queues to -smp N > vhost-user-blk: default num_queues to -smp N The series looks good to me: Reviewed-by: Stefano Garzarella Thanks, Stefano