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Re: [Qemu-devel] [PATCH 2/2] raw-posix: add Linux native AIO support

From: Avi Kivity
Subject: Re: [Qemu-devel] [PATCH 2/2] raw-posix: add Linux native AIO support
Date: Fri, 21 Aug 2009 18:35:50 +0300
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On 08/21/2009 05:48 PM, Christoph Hellwig wrote:
On Fri, Aug 21, 2009 at 12:53:49PM +0300, Avi Kivity wrote:
+ * Queue size (per-device).
+ *
+ * XXX: eventually we need to communicate this to the guest and/or make it
+ *      tunable by the guest.  If we get more outstanding requests at a
+ *      than this we will get EAGAIN from io_submit which is communicated
+ *      the guest as an I/O error.
+ */
+#define MAX_EVENTS 128

Or, we could queue any extra requests.
That doesn't make much sense.    We'd just do an additional level of
queueing in addition to those already optimized implementation in the
guest and host kernels.  This is really just an issue of communicating
the limits we have and deal with it efficiently.  It should be a
relatively small add-on patch.

You're right, virtio and scsi already know their queue sizes, should be easy to pass it down the stack.

I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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