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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 19:38:45 +0200 |
On Thu, Nov 17, 2016 at 01:27:49PM +0000, Stefan Hajnoczi wrote:
> On Thu, Nov 17, 2016 at 12:17:57AM +0200, Michael S. Tsirkin wrote:
> > 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.
>
> Good idea. I reran this morning without any tracing and compared
> against bare metal.
>
> Total reads for a 30-second 4 KB random read benchmark with 4 processes
> x iodepth=8:
>
> Bare metal: 26440 MB
> Unpatched: 19799 MB
> Patched: 21252 MB
>
> Patched vs Unpatched: +7% improvement
> Patched vs Bare metal: 20% virtualization overhead
>
> The disk image is a 8 GB raw file on XFS on LVM on dm-crypt on a Samsung
> MZNLN256HCHP 256 GB SATA SSD. This is just my laptop.
>
> Seems like a worthwhile improvement to me.
>
> Stefan
Sure. Pls remember to ping or re-post after the release.
[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, 2016/11/16
Re: [Qemu-devel] [PATCH 0/3] virtio: disable notifications in blk and scsi, Christian Borntraeger, 2016/11/17