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Date: Tue, 8 Sep 2015 14:48:25 +0100
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20150908134825.GA19999@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH] virtio-blk: use
 blk_io_plug/unplug for Linux AIO batching
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: atheurer@redhat.com, Kevin Wolf <kwolf@redhat.com>, qemu-block@nongnu.org, psuriset@redhat.com, qemu-devel@nongnu.org, Ming Lei <tom.leiming@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>

On Mon, Jul 20, 2015 at 04:54:16PM +0100, Stefan Hajnoczi wrote:
> The raw-posix block driver implements Linux AIO batching so multiple
> requests can be submitted with a single io_submit(2) system call.
> Batching is currently only used by virtio-scsi and
> virtio-blk-data-plane.
> 
> Enable batching for regular virtio-blk so the number of io_submit(2)
> system calls is reduced for workloads with queue depth > 1.
> 
> In 4KB random read performance tests with queue depth 32, the CPU
> utilization on the host is reduced by 9.4%.  The fio job is as follows:
> 
>   [global]
>   bs=4k
>   ioengine=libaio
>   iodepth=32
>   direct=1
>   sync=0
>   time_based=1
>   runtime=30
>   clocksource=gettimeofday
>   ramp_time=5
> 
>   [job1]
>   rw=randread
>   filename=/dev/vdb
>   size=4096M
>   write_bw_log=fio
>   write_iops_log=fio
>   write_lat_log=fio
>   log_avg_msec=1000
> 
> This benchmark was run on an raw image on LVM.  The disk was an SSD
> drive and -drive cache=none,aio=native was used.
> 
> Tested-by: Pradeep Surisetty <psuriset@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>  hw/block/virtio-blk.c | 4 ++++
>  1 file changed, 4 insertions(+)

Thanks, applied to my master tree:
https://github.com/stefanha/qemu/commits/master

Stefan