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Re: [Qemu-devel] [PATCH 0/3] virtio: disable notifications in blk and sc
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH 0/3] virtio: disable notifications in blk and scsi |
Date: |
Thu, 17 Nov 2016 00:17:57 +0200 |
On Wed, Nov 16, 2016 at 09:53:06PM +0000, Stefan Hajnoczi wrote:
> Disabling notifications during virtqueue processing reduces the number of
> exits. The virtio-net device already uses virtio_queue_set_notifications()
> but
> virtio-blk and virtio-scsi do not.
>
> The following benchmark shows a 15% reduction in virtio-blk-pci MMIO exits:
>
> (host)$ qemu-system-x86_64 \
> -enable-kvm -m 1024 -cpu host \
> -drive if=virtio,id=drive0,file=f24.img,format=raw,\
> cache=none,aio=native
> (guest)$ fio # jobs=4, iodepth=8, direct=1, randread
> (host)$ sudo perf record -a -e kvm:kvm_fast_mmio
>
> Number of kvm_fast_mmio events:
> Unpatched: 685k
> Patched: 592k (-15%, lower is better)
Any chance to see a gain in actual benchmark numbers?
This is important to make sure we are not just
shifting overhead around.
> Note that a workload with iodepth=1 and a single thread will not benefit -
> this
> is a batching optimization. The effect should be strongest with large iodepth
> and multiple threads submitting I/O. The guest I/O scheduler also affects the
> optimization.
>
> Stefan Hajnoczi (3):
> virtio: add missing vdev->broken check
> virtio-blk: suppress virtqueue kick during processing
> virtio-scsi: suppress virtqueue kick during processing
>
> hw/block/virtio-blk.c | 18 ++++++++++++------
> hw/scsi/virtio-scsi.c | 36 +++++++++++++++++++++---------------
> hw/virtio/virtio.c | 4 ++++
> 3 files changed, 37 insertions(+), 21 deletions(-)
>
> --
> 2.7.4
[Qemu-devel] [PATCH 3/3] virtio-scsi: suppress virtqueue kick during processing, Stefan Hajnoczi, 2016/11/16
Re: [Qemu-devel] [PATCH 0/3] virtio: disable notifications in blk and scsi,
Michael S. Tsirkin <=
Re: [Qemu-devel] [PATCH 0/3] virtio: disable notifications in blk and scsi, Christian Borntraeger, 2016/11/17