From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1MIhy7-0004zz-WF for qemu-devel@nongnu.org; Mon, 22 Jun 2009 07:45:48 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1MIhy4-0004zG-02 for qemu-devel@nongnu.org; Mon, 22 Jun 2009 07:45:47 -0400 Received: from [199.232.76.173] (port=52335 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1MIhy3-0004zD-OS for qemu-devel@nongnu.org; Mon, 22 Jun 2009 07:45:43 -0400 Received: from mx2.redhat.com ([66.187.237.31]:48136) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1MIhy3-0003kc-25 for qemu-devel@nongnu.org; Mon, 22 Jun 2009 07:45:43 -0400 Message-ID: <4A3F6EA3.2010303@redhat.com> Date: Mon, 22 Jun 2009 13:44:35 +0200 From: Kevin Wolf MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] block-raw: Make cache=off default again References: <1245669483-7076-1-git-send-email-kwolf@redhat.com> <20090622113524.GA13583@lst.de> In-Reply-To: <20090622113524.GA13583@lst.de> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: qemu-devel@nongnu.org Christoph Hellwig schrieb: > On Mon, Jun 22, 2009 at 01:18:03PM +0200, Kevin Wolf wrote: >> Since the patch that suggested it woudl revert qcow2 to writeback caching, in >> fact none of the drivers has had cache=off as default any more. This patch >> restores the desired behaviour. > > Looks good to me. I still quite hate that BDRV_O_CACHE_DEF thing, just > makes it too complicated for drivers to get it right. Actually it's just raw that must get it right. All the other drivers access their image file through raw. > Btw, what is the performance for qcow2 without write-back caching with > all your improvements? I haven't done real benchmarks for some time, but my simple test cases like "run mke2fs on an empty image" have shown great improvement (at least on IDE, for virtio I haven't understood yet what influences the size of its requests - you should have received a private mail from Dor about this). Possibly we could even enable cache=off for qcow2 now. IIUC, you have a nice setup to measure block performance now. Maybe you'd like to let it run with qcow2 and cache=wb/none? Kevin