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Re: [PATCH v2 0/4] virtio-pci: enable blk and scsi multi-queue by defaul
Re: [PATCH v2 0/4] virtio-pci: enable blk and scsi multi-queue by default
Mon, 27 Jan 2020 10:59:42 +0100
On Fri, Jan 24, 2020 at 10:01:55AM +0000, Stefan Hajnoczi wrote:
> * 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]
> Enabling multi-queue on virtio-pci storage devices improves performance on SMP
> guests because the completion interrupt is handled on the vCPU that submitted
> the I/O request. This avoids IPIs inside the guest.
> 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 benchmark
> results can vary noticably between runs.)
> 3. Users may bind the application to the vCPU that handles completion
> Set the number of queues to the number of vCPUs by default. Older machine
> types continue to default to 1 queue for live migration compatibility.
> This patch improves IOPS by 1-4% on an Intel Optane SSD with 4 vCPUs, -drive
> aio=native, and fio bs=4k direct=1 rw=randread.
> 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 <address@hidden>