From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:41768) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLy40-00012h-1r for qemu-devel@nongnu.org; Thu, 03 Nov 2011 10:14:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RLy3u-0007IA-Cn for qemu-devel@nongnu.org; Thu, 03 Nov 2011 10:14:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:2526) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RLy3u-0007Hv-5k for qemu-devel@nongnu.org; Thu, 03 Nov 2011 10:14:34 -0400 Message-ID: <4EB2A280.3080806@redhat.com> Date: Thu, 03 Nov 2011 15:17:36 +0100 From: Kevin Wolf MIME-Version: 1.0 References: <1318866452-30026-1-git-send-email-stefanha@linux.vnet.ibm.com> <1318866452-30026-4-git-send-email-stefanha@linux.vnet.ibm.com> In-Reply-To: <1318866452-30026-4-git-send-email-stefanha@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC 3/6] block: wait for overlapping requests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Paolo Bonzini , Marcelo Tosatti , qemu-devel@nongnu.org Am 17.10.2011 17:47, schrieb Stefan Hajnoczi: > When copy-on-read is enabled it is necessary to wait for overlapping > requests before issuing new requests. This prevents races between the > copy-on-read and a write request. > > Signed-off-by: Stefan Hajnoczi This doesn't only order guest request against COR requests, but also makes guest requests wait on each other. It's probably not a big problem, but if we had to optimise performance with COR later, this is something to remember. Doing an optimisation that only requests of different type are ordered wouldn't be too hard, though maybe avoiding starvation of the other type could get a bit harder. Let's leave it as it is for now. Kevin