From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:52429) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QAlbt-0005Nr-0a for qemu-devel@nongnu.org; Fri, 15 Apr 2011 12:11:06 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QAlbn-0003N1-9B for qemu-devel@nongnu.org; Fri, 15 Apr 2011 12:11:04 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:43556) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QAlbn-0003M9-5N for qemu-devel@nongnu.org; Fri, 15 Apr 2011 12:10:59 -0400 Received: from d01relay07.pok.ibm.com (d01relay07.pok.ibm.com [9.56.227.147]) by e9.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p3FFggXu004454 for ; Fri, 15 Apr 2011 11:42:42 -0400 Received: from d01av03.pok.ibm.com (d01av03.pok.ibm.com [9.56.224.217]) by d01relay07.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p3FGAeen2744410 for ; Fri, 15 Apr 2011 12:10:40 -0400 Received: from d01av03.pok.ibm.com (loopback [127.0.0.1]) by d01av03.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p3FGAdUP030138 for ; Fri, 15 Apr 2011 13:10:40 -0300 Message-ID: <4DA86DFD.2020000@us.ibm.com> Date: Fri, 15 Apr 2011 11:10:37 -0500 From: Anthony Liguori MIME-Version: 1.0 References: <1302874855-14736-1-git-send-email-stefanha@linux.vnet.ibm.com> <20110415150513.GA29619@lst.de> <20110415153448.GA30116@lst.de> In-Reply-To: <20110415153448.GA30116@lst.de> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] raw-posix: Linearize direct I/O on Linux NFS List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: Kevin Wolf , Stefan Hajnoczi , Stefan Hajnoczi , qemu-devel@nongnu.org, Khoa Huynh , pbadari@linux.vnet.ibm.com On 04/15/2011 10:34 AM, Christoph Hellwig wrote: > On Fri, Apr 15, 2011 at 04:26:41PM +0100, Stefan Hajnoczi wrote: >> On Fri, Apr 15, 2011 at 4:05 PM, Christoph Hellwig wrote: >>> NAK. ?Just wait for the bloody NFS client fix to get in instead of >>> adding crap like that. >> That's totally fine if NFS client will be fixed in the near future but >> this doesn't seem likely: >> >> http://www.spinics.net/lists/linux-nfs/msg20462.html > The code to use preadv/pwritev has been in qemu for over 2 years, > and it took people to notice the NFS slowdown until now, so don't > expect it to be fixed three days layer. > > I can't event see you in the relevent threads arguing for getting it > fixed, so don't complain. In general, since we are userspace, we should try to run well on whatever kernel we're on. What I don't like about this patch is that likelihood of false positives. We check for Linux and for NFS but that means an old userspace is doing unoptimal things on newer kernels. Even if we had a kernel version check, if the fix gets backported to an older kernel, we'll still get a false positive. Ideally, we'd be able to query the kernel to see whether we should bounce or not. But AFAIK there is nothing even close to an interface to do this today. Regards, Anthony Liguori