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Date: Wed, 28 Nov 2007 14:34:02 +0000
From: Samuel Thibault <samuel.thibault@eu.citrix.com>
Subject: Re: [Qemu-devel] [PATCH 0/2] Open disk images with O_DIRECT
Message-ID: <20071128143402.GG4083@implementation.uk.xensource.com>
References: <11962585701617@bull.net> <20071128142739.GA7379@redhat.com>
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To: "Daniel P. Berrange" <berrange@redhat.com>, qemu-devel@nongnu.org
Cc: Laurent Vivier <Laurent.Vivier@bull.net>

Daniel P. Berrange, le Wed 28 Nov 2007 14:27:39 +0000, a écrit :
> On Wed, Nov 28, 2007 at 03:02:50PM +0100, Laurent Vivier wrote:
> > These patches allow to open file using O_DIRECT and bypass the host I/O cache.
> >
> > [PATCH 1/2] Add "directio" parameter to "-drive"
> > 
> >     Using "directio=on" with "-drive" will open the disk image 
> >     file using "O_DIRECT".
> 
> I don't see the point in adding a config param for this. If it provides a
> useful performance improvement (or other benefit) we should enable it by 
> default all the time.

That depends on the mileage of the user.  Sometimes it is useful since
it avoids the duplication of page or buffer cache between the guest and
the host, sometimes it is not because the guest is not so i/o friendly
and hence using the host page/buffer cache is useful.

Samuel