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Re: [Qemu-devel] [PATCH v3 0/7] virtio-blk: multiqueue support
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v3 0/7] virtio-blk: multiqueue support |
Date: |
Tue, 21 Jun 2016 10:06:29 +0100 |
User-agent: |
Mutt/1.6.1 (2016-04-27) |
On Mon, Jun 20, 2016 at 03:29:43PM +0200, Roman Penyaev wrote:
> Hi, Stefan.
>
> On Mon, Jun 20, 2016 at 12:36 PM, Stefan Hajnoczi <address@hidden> wrote:
> > On Tue, Jun 07, 2016 at 05:28:24PM +0100, Stefan Hajnoczi wrote:
> >> v3:
> >> * Drop Patch 1 to batch guest notify for non-dataplane
> >>
> >> The Linux AIO completion BH and the virtio-blk batch notify BH changed
> >> order
> >> in the AioContext->first_bh list as a side-effect of moving the BH from
> >> hw/block/dataplane/virtio-blk.c to hw/block/virtio-blk.c. This caused a
> >> serious performance regression for both dataplane and non-dataplane.
> >>
> >> I've decided not to move the BH in this series and work on a separate
> >> solution for making batch notify generic.
> >>
> >> The remaining patches have been reordered and cleaned up.
> >>
> >> * See performance data below.
> >>
> >> v2:
> >> * Simplify s->rq live migration [Paolo]
> >> * Use more efficient bitmap ops for batch notification [Paolo]
> >> * Fix perf regression due to batch notify BH in wrong AioContext
> >> [Christian]
> >>
> >> The virtio_blk guest driver has supported multiple virtqueues since Linux
> >> 3.17.
> >> This patch series adds multiple virtqueues to QEMU's virtio-blk emulated
> >> device.
> >>
> >> Ming Lei sent patches previously but these were not merged. This series
> >> implements virtio-blk multiqueue for QEMU from scratch since the codebase
> >> has
> >> changed. Live migration support for s->rq was also missing from the
> >> previous
> >> series and has been added.
> >>
> >> It's important to note that QEMU's block layer does not support multiqueue
> >> yet.
> >> Therefore virtio-blk device processes all virtqueues in the same AioContext
> >> (IOThread). Further work is necessary to take advantage of multiqueue
> >> support
> >> in QEMU's block layer once it becomes available.
> >>
> >> Performance results:
> >>
> >> Using virtio-blk-pci,num-queues=4 can produce a speed-up but -smp 4
> >> introduces a lot of variance across runs. No pinning was performed.
> >>
> >> Results show that there is no regression anymore, thanks to dropping the
> >> batch notify BH patch.
> >>
> >> RHEL 7.2 guest on RHEL 7.2 host with 1 vcpu and 1 GB RAM unless otherwise
> >> noted. The default configuration of the Linux null_blk driver is used as
> >> /dev/vdb.
> >>
> >> $ cat files/fio.job
> >> [global]
> >> filename=/dev/vdb
> >> ioengine=libaio
> >> direct=1
> >> runtime=60
> >> ramp_time=5
> >> gtod_reduce=1
> >>
> >> [job1]
> >> numjobs=4
> >> iodepth=16
> >> rw=randread
> >> bs=4K
> >>
> >> $ ./analyze.py runs/
> >> Name IOPS Error
> >> unpatched-d6550e9ed2 19269820.2 ± 1.36%
> >> unpatched-dataplane-d6550e9ed2 22351400.4 ± 1.07%
> >> v3-dataplane 22318511.2 ± 0.77%
> >> v3-no-dataplane 18936103.8 ± 1.12%
> >> v3-queues-4-no-dataplane 19177021.8 ± 1.45%
> >> v3-smp-4-no-dataplane 25509585.2 ± 29.50%
> >> v3-smp-4-no-dataplane-no-mq 12466177.2 ± 7.88%
> >>
> >> Configuration:
> >> Name Patched? Dataplane? SMP? MQ?
> >> unpatched-d6550e9ed2 N N N N
> >> unpatched-dataplane-d6550e9ed2 N Y N N
> >> v3-dataplane Y Y N N
> >> v3-no-dataplane Y N N N
> >> v3-queues-4-no-dataplane Y N N Y
> >> v3-smp-4-no-dataplane Y N Y Y
> >> v3-smp-4-no-dataplane-no-mq Y N Y N
> >>
> >> SMP means -smp 4.
> >> MQ means virtio-blk-pci,num-queues=4.
> >>
> >> Stefan Hajnoczi (7):
> >> virtio-blk: add VirtIOBlockConf->num_queues
> >> virtio-blk: multiqueue batch notify
> >> virtio-blk: tell dataplane which vq to notify
> >> virtio-blk: associate request with a virtqueue
> >> virtio-blk: live migrate s->rq with multiqueue
> >> virtio-blk: dataplane multiqueue support
> >> virtio-blk: add num-queues device property
> >>
> >> hw/block/dataplane/virtio-blk.c | 81
> >> +++++++++++++++++++++++++++++------------
> >> hw/block/dataplane/virtio-blk.h | 2 +-
> >> hw/block/virtio-blk.c | 52 +++++++++++++++++++++-----
> >> include/hw/virtio/virtio-blk.h | 6 ++-
> >> 4 files changed, 105 insertions(+), 36 deletions(-)
> >
> > Ping?
>
> I have one minor note regarding the following test:
>
> "Name Patched? Dataplane? SMP? MQ?"
> "v3-queues-4-no-dataplane Y N N Y"
>
> If I am not mistaken and understand your test description, it does not
> make a lot sense to use queues when you have VCPUs=1 (i.e. SMP=N),
> because block layer will not create nr_queues > CPUs number. So what
> I want to say is that in this test even you specify num_queues=4 for
> virtio_blk, only 1 software queue will be created by the guest block
> layer and then it will be mapped to only 1 HW queue, even you have
> requested 4. On host userspace side you will always receive IO in the
> queue #0.
Good point.
> And I've rebased and tested all my changes on top of your latest v3 set.
> The question is: are you interested in this up-to-date RFC of mine:
> "simple multithreaded MQ implementation for bdrv_raw" which I sent
> couple of weeks ago? I can resend it by single merged commit once more.
If it's not too much work updating the RFC then I think it's useful.
Others may wish to experiment with your series to gather performance
numbers, especially for comparision when the QEMU block layer becomes mq
capable.
Stefan
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- [Qemu-devel] [PATCH v3 4/7] virtio-blk: associate request with a virtqueue, (continued)
- [Qemu-devel] [PATCH v3 4/7] virtio-blk: associate request with a virtqueue, Stefan Hajnoczi, 2016/06/08
- [Qemu-devel] [PATCH v3 2/7] virtio-blk: multiqueue batch notify, Stefan Hajnoczi, 2016/06/08
- [Qemu-devel] [PATCH v3 1/7] virtio-blk: add VirtIOBlockConf->num_queues, Stefan Hajnoczi, 2016/06/08
- [Qemu-devel] [PATCH v3 5/7] virtio-blk: live migrate s->rq with multiqueue, Stefan Hajnoczi, 2016/06/08
- [Qemu-devel] [PATCH v3 6/7] virtio-blk: dataplane multiqueue support, Stefan Hajnoczi, 2016/06/08
- [Qemu-devel] [PATCH v3 7/7] virtio-blk: add num-queues device property, Stefan Hajnoczi, 2016/06/08
- Re: [Qemu-devel] [PATCH v3 0/7] virtio-blk: multiqueue support, Stefan Hajnoczi, 2016/06/20