From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:41565) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QAliU-0006ii-Nl for qemu-devel@nongnu.org; Fri, 15 Apr 2011 12:17:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QAliO-0005Kd-SU for qemu-devel@nongnu.org; Fri, 15 Apr 2011 12:17:54 -0400 Received: from mail-gy0-f173.google.com ([209.85.160.173]:45301) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QAliO-0005KZ-Oj for qemu-devel@nongnu.org; Fri, 15 Apr 2011 12:17:48 -0400 Received: by gyg4 with SMTP id 4so1122429gyg.4 for ; Fri, 15 Apr 2011 09:17:48 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <4DA86DFD.2020000@us.ibm.com> References: <1302874855-14736-1-git-send-email-stefanha@linux.vnet.ibm.com> <20110415150513.GA29619@lst.de> <20110415153448.GA30116@lst.de> <4DA86DFD.2020000@us.ibm.com> Date: Fri, 15 Apr 2011 17:17:47 +0100 Message-ID: From: Stefan Hajnoczi Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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: Anthony Liguori Cc: Kevin Wolf , Stefan Hajnoczi , qemu-devel@nongnu.org, Khoa Huynh , pbadari@linux.vnet.ibm.com, Christoph Hellwig On Fri, Apr 15, 2011 at 5:10 PM, Anthony Liguori wrot= e: > 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 =A0wrote= : >>>> >>>> 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. > =A0We check for Linux and for NFS but that means an old userspace is doin= g > unoptimal things on newer kernels. =A0Even if we had a kernel version che= ck, > 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. =A0But AFAIK there is nothing even close to an interface to do this > today. Bah, good point. I was planning to sneak in a uname() later but that really doesn't cut it due to backports/downstream. Stefan