Re: [Qemu-devel] [PATCH v1 3/3] dataplane: submit I/O at batch

[Paolo Bonzini <pbonzini@redhat.com>]

Il 30/06/2014 17:47, Ming Lei ha scritto:
> Before commit 580b6b2aa2(dataplane: use the Qemu block
> layer for I/O), dataplane for virtio-blk submits block
> I/O at batch.
>
> This commit 580b6b2aa2 replaces the custom linux AIO
> implementation(including I/O batch) with Qemu block
> layer, but this commit causes ~40% throughput regression
> on virtio-blk performance, and removing submitting I/O
> at batch is one of the cause.
>
> This patch applys the new introduced bdrv_io_plug() and
> bdrv_io_unplug() interfaces to support submitting I/O
> at batch for Qemu block layer, and in my test, the change
> can improve thoughput by ~30% with 'aio=native'.
>
> Following my fio test script:
>
> 	[global]
> 	direct=1
> 	size=4G
> 	bsrange=4k-4k
> 	timeout=40
> 	numjobs=4
> 	ioengine=libaio
> 	iodepth=64
> 	filename=/dev/vdc
> 	group_reporting=1
>
> 	[f]
> 	rw=randread
>
> Result on one of my small machine(host: x86_64, 2cores, 4thread, guest: 4cores):
> 	- qemu master: 59K IOPS
> 	- qemu master with these patches: 81K IOPS
> 	- 2.0.0 release(dataplane using custom linux aio): 104K IOPS
>
> Signed-off-by: Ming Lei <ming.lei@canonical.com>
> ---
>  hw/block/dataplane/virtio-blk.c |    2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/hw/block/dataplane/virtio-blk.c b/hw/block/dataplane/virtio-blk.c
> index c10b7b7..8fefcce 100644
> --- a/hw/block/dataplane/virtio-blk.c
> +++ b/hw/block/dataplane/virtio-blk.c
> @@ -289,6 +289,7 @@ static void handle_notify(EventNotifier *e)
>      int ret;
>
>      event_notifier_test_and_clear(&s->host_notifier);
> +    bdrv_io_plug(s->blk->conf.bs);
>      for (;;) {
>          /* Disable guest->host notifies to avoid unnecessary vmexits */
>          vring_disable_notification(s->vdev, &s->vring);
> @@ -322,6 +323,7 @@ static void handle_notify(EventNotifier *e)
>              break;
>          }
>      }
> +    bdrv_io_unplug(s->blk->conf.bs);
>  }
>
>  /* Context: QEMU global mutex held */
>

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

but please add it to the non-dataplane path as well, and to virtio-scsi.

Paolo