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[Qemu-devel] [PATCH] qcow2: improve I/O performance with cache=off


From: Laurent Vivier
Subject: [Qemu-devel] [PATCH] qcow2: improve I/O performance with cache=off
Date: Fri, 20 Jun 2008 16:38:00 +0200

Hi,

this patch improves qcow2 I/O performance when used with cache=off.

It modifies qcow_aio_[read|write]_cb() to read as many clusters as
possible per bdrv_aio_[read|write]().

I've made some tests with dbench:

                                WITHOUT PATCH   WITH PATCH

ide, cache=off,snapshot=off     20.8494 MB/sec  24.0711 MB/sec
ide, cache=off,snapshot=on      20.9349 MB/sec  24.5031 MB/sec
scsi,cache=off,snapshot=off     21.0264 MB/sec  24.6119 MB/sec
scsi,cache=off,snapshot=on      21.4184 MB/sec  24.6739 MB/sec

The gain is approximately 15%.

Regards,
Laurent
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Attachment: qcow2.patch
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