From: Stefan Hajnoczi <stefanha@gmail.com>
To: Yaodong Yang <yaodong.yangy@icloud.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"qemu-discuss@nongnu.org" <qemu-discuss@nongnu.org>
Subject: Re: [Qemu-devel] About the IO queue inside qemu
Date: Wed, 2 Oct 2013 12:16:37 +0200 [thread overview]
Message-ID: <20131002101637.GM2142@stefanha-thinkpad.redhat.com> (raw)
In-Reply-To: <99E88309-FA7E-4A47-AF07-B83E5C1134AE@icloud.com>
On Wed, Oct 02, 2013 at 01:28:11AM -0500, Yaodong Yang wrote:
> I'm wondering is there any io queue inside qemu? Is there any IO scheduling inside it? I notice that there is an IO track feature inside block.c, but I do not know the purpose of it. Could someone explain it for me? Thanks a lot!
There are two queues:
1. Throttled requests. Used by the I/O throttling feature (-drive
iops=5000). Requests need to be suspended until there is enough
budget for them.
2. Tracked requests. This is a generic queue that is used by the
copy-on-read feature to prevent corruption when the guest writes to a
sector that is currently being copied.
There is also an API to batch writes so they can be merged. virtio-blk
uses this and may therefore change the I/O pattern.
Stefan
prev parent reply other threads:[~2013-10-02 10:16 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-10-02 6:28 [Qemu-devel] About the IO queue inside qemu Yaodong Yang
2013-10-02 10:16 ` Stefan Hajnoczi [this message]
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