From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1G6YyS-0006zY-J0 for qemu-devel@nongnu.org; Fri, 28 Jul 2006 16:30:20 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1G6YyQ-0006xI-Og for qemu-devel@nongnu.org; Fri, 28 Jul 2006 16:30:20 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1G6YyQ-0006x9-G1 for qemu-devel@nongnu.org; Fri, 28 Jul 2006 16:30:18 -0400 Received: from [65.74.133.4] (helo=mail.codesourcery.com) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA:32) (Exim 4.52) id 1G6Z0U-00012n-38 for qemu-devel@nongnu.org; Fri, 28 Jul 2006 16:32:26 -0400 From: Paul Brook Subject: Re: [Qemu-devel] Re: [RFC][PATCH] make sure disk writes actually =?utf-8?q?hit=09disk?= Date: Fri, 28 Jul 2006 21:30:09 +0100 References: <44CA6B76.7000004@redhat.com> <44CA7102.1020402@redhat.com> In-Reply-To: <44CA7102.1020402@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200607282130.11255.paul@codesourcery.com> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: alan@redhat.com > > With a proper async API, is there any reason why we would want this to be > > tunable? I don't think there's much of a benefit of prematurely claiming > > a write is complete especially once the SCSI emulation can support > > multiple simultaneous requests. > > You're right. This O_SYNC bandaid should probably stay in place > to prevent data corruption, until the AIO framework is ready to > be used. It's arguable whether O_SYNC is needed at all. Qemu doesn't claim data is written to disk, and provides facilities for the guest OS to flush the cache, just like real hardware does. Have you measured the impact of O_SYNC? I wouldn't be surprised if it was significant. Paul