Re: [Qemu-devel] [PATCH v6 0/3] linux-aio: introduce submit I/O as a batch

[Stefan Hajnoczi]

On Fri, Jul 04, 2014 at 06:04:32PM +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 for scsi devies, which
>     need some changes to linux-aio
> 
> V6:
>       - fix requests leak if part of them arn't submitted successfully,
>       pointed by Stefan
>       - linux-aio.c coding style fix
> 
> V5:
>       - rebase on v2.1.0-rc0 of qemu.git/master
>       - block/linux-aio.c code style fix
>       - don't flush io queue before flush, pointed by Paolo
> 
> 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, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

In Patch 2 we should complete requests with -EIO if io_submit() returned
0 <= ret < len.  I fixed this up when applying because the patch was
completing with a bogus ret value.

Stefan

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