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Re: [Qemu-devel] [Qemu-block] [PATCH v4 8/8] linux-aio: share one LinuxA
Re: [Qemu-devel] [Qemu-block] [PATCH v4 8/8] linux-aio: share one LinuxAioState within an AioContext
Tue, 10 May 2016 12:32:27 +0200
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On 10/05/2016 11:40, Kevin Wolf wrote:
> > Regarding performance, I'm thinking about a guest with 8 disks (queue
> > depth 32). The worst case is when the guest submits 32 requests at once
> > but the Linux AIO event limit has already been reached. Then the disk
> > is starved until other disks' requests complete.
> Sounds like a valid concern.
Oh, so you're concerned about the non-dataplane case. My suspicion is
that, with such a number of outstanding I/O, you probably have bad
performance unless you use dataplane.
Also, aio=threads has had a 64 I/O limit for years and we've never heard
about problems with stuck I/O. But I agree that it's one area to keep
an eye on.