From: Avi Kivity <avi@qumranet.com>
To: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] qcow2: improve I/O performance with cache=off
Date: Mon, 23 Jun 2008 05:50:03 +0300 [thread overview]
Message-ID: <485F0F5B.6060002@qumranet.com> (raw)
In-Reply-To: <1213972680.3859.34.camel@frecb07144>
Laurent Vivier wrote:
> 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]().
>
>
Write allocation is still slow though. For fixing this, I think the
only way is to modify get_cluster_offset() to accept and return an extent.
> 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%.
>
I don't think dbench is a good test for this as it involves the guest
pagecache. 'dd' or 'fio' would be much more indicative.
--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.
next prev parent reply other threads:[~2008-06-23 2:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-20 14:38 [Qemu-devel] [PATCH] qcow2: improve I/O performance with cache=off Laurent Vivier
2008-06-23 2:50 ` Avi Kivity [this message]
2008-06-24 15:40 ` Kevin Wolf
2008-06-24 16:40 ` Laurent Vivier
2008-06-25 8:43 ` Kevin Wolf
2008-06-25 8:59 ` Laurent Vivier
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