Re: [Qemu-devel] [PATCH v4 0/3] linux-aio: introduce submit I/O as a batch

[Stefan Hajnoczi <stefanha@gmail.com>]

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On Wed, Jul 02, 2014 at 08:18:45PM +0800, Ming Lei wrote:
> Hi,
> 
> The commit 580b6b2aa2(dataplane: use the QEMU block layer for I/O)
> introduces ~40% throughput regression on virtio-blk dataplane, and
> one of causes is that submitting I/O as a batch is removed.
> 
> This patchset trys to introduce this mechanism on block, at least,
> linux-aio can benefit from that.
> 
> With these patches, it is observed that thoughout on virtio-blk
> dataplane can be improved a lot, see data in commit log of patch
> 3/3.
> 
> It should be possible to apply the batch mechanism to other devices
> (such as virtio-scsi) too.
> 
> TODO:
> 	- support queuing I/O to multi files which need lots of change
>     to linux-aio for scsi devies
> 
> V4:
> 	- support other non-raw formats with under-optimized performance
>     - use reference counter for plug & unplug
>     - flush io queue before sending flush command
> 
> V3:
> 	- only support submitting I/O as a batch for raw format, pointed by
>     Kevin
> 
> V2:
> 	- define return value of bdrv_io_unplug as void, suggested by Paolo
> 	- avoid busy-wait for handling io_submit
> V1:
> 	- move queuing io stuff into linux-aio.c as suggested by Paolo
> 
> 
> Thanks,
> --
> Ming Lei

Nice performance fix.  Together with the other fixes we've been
discussing I think we can fight a dataplane performance regression from
QEMU 2.0 to 2.1.

Looking forward to the next revision.

Stefan

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