From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1IxOX6-0005Jc-UX for qemu-devel@nongnu.org; Wed, 28 Nov 2007 10:09:00 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1IxOX3-0005Hp-6T for qemu-devel@nongnu.org; Wed, 28 Nov 2007 10:09:00 -0500 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1IxOX2-0005Hh-O1 for qemu-devel@nongnu.org; Wed, 28 Nov 2007 10:08:56 -0500 Received: from mx1.redhat.com ([66.187.233.31]) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1IxOX2-0001R4-Sk for qemu-devel@nongnu.org; Wed, 28 Nov 2007 10:08:57 -0500 Date: Wed, 28 Nov 2007 15:08:20 +0000 From: "Daniel P. Berrange" Subject: Re: [Qemu-devel] [PATCH 0/2] Open disk images with O_DIRECT Message-ID: <20071128150820.GC7379@redhat.com> References: <11962585701617@bull.net> <20071128142739.GA7379@redhat.com> <20071128143402.GG4083@implementation.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20071128143402.GG4083@implementation.uk.xensource.com> Content-Transfer-Encoding: quoted-printable Reply-To: "Daniel P. Berrange" , qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Samuel Thibault Cc: Laurent Vivier , qemu-devel@nongnu.org On Wed, Nov 28, 2007 at 02:34:02PM +0000, Samuel Thibault wrote: > Daniel P. Berrange, le Wed 28 Nov 2007 14:27:39 +0000, a =E9crit : > > 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" > > >=20 > > > Using "directio=3Don" with "-drive" will open the disk image=20 > > > file using "O_DIRECT". > >=20 > > I don't see the point in adding a config param for this. If it provid= es a > > useful performance improvement (or other benefit) we should enable it= by=20 > > default all the time. >=20 > 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. I don't buy that - all OS already do I/O caching because its useful even on baremetal. As an end-user how do you decide whether to turn on the directoio=3Don/off option or not ? Most people won't notice it & will ju= st run with the default setting - those who do notice are just subjected to trial-and-error to figure out whether the setting is any use. IMHO, QEMU should just pick the best setting. Dan. --=20 |=3D- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 24= 96 -=3D| |=3D- Perl modules: http://search.cpan.org/~danberr/ = -=3D| |=3D- Projects: http://freshmeat.net/~danielpb/ = -=3D| |=3D- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 950= 5 -=3D|=20