From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KppXH-0003uL-S7 for qemu-devel@nongnu.org; Tue, 14 Oct 2008 15:26:27 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KppXD-0003sF-6u for qemu-devel@nongnu.org; Tue, 14 Oct 2008 15:26:27 -0400 Received: from [199.232.76.173] (port=35387 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KppXC-0003s1-Rc for qemu-devel@nongnu.org; Tue, 14 Oct 2008 15:26:22 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:39771) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1KppXC-0004Pw-Bb for qemu-devel@nongnu.org; Tue, 14 Oct 2008 15:26:22 -0400 Subject: Re: [Qemu-devel] [RFC] Disk integrity in QEMU From: Laurent Vivier In-Reply-To: <48F4B904.6000608@redhat.com> References: <48EE38B9.2050106@codemonkey.ws> <48EF1D55.7060307@redhat.com> <48F0E83E.2000907@redhat.com> <48F10DFD.40505@codemonkey.ws> <20081012004401.GA9763@acer.localdomain> <48F1CF9E.9030500@redhat.com> <48F23AF1.2000104@codemonkey.ws> <48F24320.9010201@redhat.com> <48F25720.9010306@codemonkey.ws> <48F26171.70109@redhat.com> <48F2681A.1030401@codemonkey.ws> <48F4B904.6000608@redhat.com> Content-Type: text/plain; charset=utf-8 Date: Tue, 14 Oct 2008 21:25:41 +0200 Message-Id: <1224012341.4177.6.camel@frecb07144> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Chris Wright , Mark McLoughlin , kvm-devel , qemu-devel@nongnu.org, Ryan Harper Le mardi 14 octobre 2008 =C3=A0 17:21 +0200, Avi Kivity a =C3=A9crit : > Anthony Liguori wrote: > > Avi Kivity wrote: > >> Given that we don't have a zero-copy implementation yet, it is > >> impossible to generate real performance data. > > > > Which means that it's premature to suggest switching the default to > > O_DIRECT since it's not going to help right now. It can be revisited > > once we can do zero copy but again, I think it should be driven by > > actual performance data. My main point is that switching to O_DIRECT > > right now is only going to hurt performance for some users, and most > > likely help no one. >=20 > I am assuming that we will provide true O_DIRECT support soon. If you remember, I tried to introduce zero copy when I wrote the "cache=3Doff" patch: http://thread.gmane.org/gmane.comp.emulators.qemu/22148/focus=3D22149 but it was not correct (see Fabrice comment). Laurent --=20 ------------------ Laurent.Vivier@bull.net ------------------ "Tout ce qui est impossible reste =C3=A0 accomplir" Jules Verne "Things are only impossible until they're not" Jean-Luc Picard