From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=42118 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Q0Xua-00055U-Uz for qemu-devel@nongnu.org; Fri, 18 Mar 2011 07:32:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Q0XuY-0003yy-7D for qemu-devel@nongnu.org; Fri, 18 Mar 2011 07:32:08 -0400 Received: from mx1.redhat.com ([209.132.183.28]:14034) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Q0XuX-0003yd-SE for qemu-devel@nongnu.org; Fri, 18 Mar 2011 07:32:06 -0400 Message-ID: <4D834331.6000907@redhat.com> Date: Fri, 18 Mar 2011 12:34:09 +0100 From: Kevin Wolf MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 6/6] ide: Avoid canceling IDE DMA References: <1280846670-27063-1-git-send-email-kwolf@redhat.com> <1280846670-27063-7-git-send-email-kwolf@redhat.com> <20110318111941.GA25520@lst.de> In-Reply-To: <20110318111941.GA25520@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 Am 18.03.2011 12:19, schrieb Christoph Hellwig: > On Tue, Aug 03, 2010 at 04:44:30PM +0200, Kevin Wolf wrote: >> Furthermore because the DMA operation is splitted into many synchronous >> aio_read/write if there's more than one entry in the SG table, without this >> patch the DMA would be cancelled in the middle, something we've no idea if it >> happens on real hardware too or not. Overall this seems a great risk for zero >> gain. > > That hasn't been true for a long time when this code was commited, at least > on kernel supporting preadv/pwritev and/or aio. So what do you want to tell us? Should the patch be reverted? I think the request can still be split in multiple bdrv_aio_readv/writev calls in dma-helpers.c and in non-raw block drivers, so we would still cancel somewhere in the middle. Kevin