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Date: Tue, 1 Sep 2009 01:09:02 +0200
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [PATCH 1/4] block: add enable_write_cache flag
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To: Jamie Lokier <jamie@shareable.org>
Cc: Christoph Hellwig <hch@lst.de>, qemu-devel@nongnu.org

On Tue, Sep 01, 2009 at 01:06:46AM +0200, Christoph Hellwig wrote:
> On Mon, Aug 31, 2009 at 11:59:25PM +0100, Jamie Lokier wrote:
> > Anthony Liguori wrote:
> > > Can someone do some benchmarking with cache=writeback and fdatasync 
> > > first and quantify what the real performance impact is?
> > 
> > Unfortunately we can't yet quantify the impact on the hardware I care
> > about (ordinary consumer PCs with non-NCQ SATA disks), because Linux
> > hosts don't *yet* implement O_SYNC or fdatasync properly.
> 
> They do if you use XFS.

And data-writeback + fdatasync also when using reiserfs.  For ext3/4 you
need the patches I sent out today, for O_SYNC on everythig but XFS also
Jan Kara's patch series.