From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:43280) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QYfie-0000lD-Pn for qemu-devel@nongnu.org; Mon, 20 Jun 2011 10:44:53 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QYfic-0005h3-5H for qemu-devel@nongnu.org; Mon, 20 Jun 2011 10:44:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5133) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QYfib-0005gq-La for qemu-devel@nongnu.org; Mon, 20 Jun 2011 10:44:49 -0400 Message-ID: <4DFF5D8B.80600@redhat.com> Date: Mon, 20 Jun 2011 16:47:39 +0200 From: Kevin Wolf MIME-Version: 1.0 References: <4DF8A4FD.6050807@redhat.com> <1308145570-18364-1-git-send-email-fsimonce@redhat.com> <20110616142809.GA9468@lst.de> <4DFA168B.9030808@redhat.com> In-Reply-To: <4DFA168B.9030808@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] qemu-img: Add cache command line option List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: Federico Simoncelli , qemu-devel@nongnu.org, kvm@vger.kernel.org, avi@redhat.com Am 16.06.2011 16:43, schrieb Kevin Wolf: > Am 16.06.2011 16:28, schrieb Christoph Hellwig: >> On Wed, Jun 15, 2011 at 09:46:10AM -0400, Federico Simoncelli wrote: >>> qemu-img currently writes disk images using writeback and filling >>> up the cache buffers which are then flushed by the kernel preventing >>> other processes from accessing the storage. >>> This is particularly bad in cluster environments where time-based >>> algorithms might be in place and accessing the storage within >>> certain timeouts is critical. >>> This patch adds the option to choose a cache method when writing >>> disk images. >> >> Allowing to chose the mode is of course fine, but what about also >> choosing a good default? writethrough doesn't really make any sense >> for qemu-img, given that we can trivially flush the cache at the end >> of the operations. I'd also say that using the buffer cache doesn't >> make sense either, as there is little point in caching these operations. > > Right, we need to keep the defaults as they are. That is, for convert > unsafe and for everything else writeback. The patch seems to make > writeback the default for everything. Federico, are you going to fix this in a v4? Kevin