Re: [Qemu-devel] [PATCH v4 3/3] dataplane: submit I/O as a batch

[Kevin Wolf]

Am 02.07.2014 um 14:18 hat Ming Lei geschrieben:
> Before commit 580b6b2aa2(dataplane: use the QEMU block
> layer for I/O), dataplane for virtio-blk submits block
> I/O as a batch.
> 
> This commit 580b6b2aa2 replaces the custom linux AIO
> implementation(including submit I/O as a batch) with QEMU
> block layer, but this commit causes ~40% throughput regression
> on virtio-blk performance, and removing submitting I/O
> as a batch is one of the causes.
> 
> This patch applies the newly 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 throughput 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
> 
> Reviewed-by: Paolo Bonzini <address@hidden>
> Signed-off-by: Ming Lei <address@hidden>

Reviewing this one doesn't make sense because commit b002254d
('virtio-blk: Unify {non-,}dataplane's request handlings') removes the
patched code. You need to patch common virtio-blk code now (which should
improve non-dataplane virtio-blk as well).

Kevin