From: Stefan Hajnoczi <stefanha@gmail.com>
To: "charlie.song" <charlie.song@ucloud.cn>
Cc: kvm <kvm@vger.kernel.org>
Subject: Re: AIO requests may be disordered by Qemu-kvm iothread with disk cache=writethrough, Bug or Feature?
Date: Wed, 14 Oct 2015 10:32:35 +0100 [thread overview]
Message-ID: <20151014093235.GA14874@stefanha-thinkpad> (raw)
In-Reply-To: <dae53c1.1a208.15047527458.Coremail.charlie.song@ucloud.cn>
On Thu, Oct 08, 2015 at 07:59:56PM +0800, charlie.song wrote:
> We recently try to use Linux AIO from guest OS and find that the IOthread mechanism of Qemu-KVM will reorder I/O requests from guest OS
> even when the AIO write requests are issued from a single thread in order. This does not happen on the host OS however.
I think you are describing a situation where a guest submits multiple
overlapping I/O requests at the same time.
virtio-blk does not guarantee a specific request ordering, so the
application needs to wait for request completion if ordering matters.
io_submit(2) also does not make guarantees about ordering.
Stefan
prev parent reply other threads:[~2015-10-14 13:51 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-08 11:59 AIO requests may be disordered by Qemu-kvm iothread with disk cache=writethrough, Bug or Feature? charlie.song
2015-10-08 15:37 ` Fam Zheng
2015-10-09 3:25 ` charlie.song
2015-10-09 4:16 ` Fam Zheng
2015-10-09 4:33 ` charlie.song
[not found] ` <56174390.80804@ucloud.cn>
2015-10-09 4:44 ` charlie.song
2015-10-14 9:32 ` Stefan Hajnoczi [this message]
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