From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:57361) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QAnft-00089D-Bx for qemu-devel@nongnu.org; Fri, 15 Apr 2011 14:23:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QAnfp-000756-0X for qemu-devel@nongnu.org; Fri, 15 Apr 2011 14:23:21 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:53003) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QAnfo-00074c-Ps for qemu-devel@nongnu.org; Fri, 15 Apr 2011 14:23:16 -0400 Received: from d03relay01.boulder.ibm.com (d03relay01.boulder.ibm.com [9.17.195.226]) by e35.co.us.ibm.com (8.14.4/8.13.1) with ESMTP id p3FI78RA023395 for ; Fri, 15 Apr 2011 12:07:08 -0600 Received: from d03av05.boulder.ibm.com (d03av05.boulder.ibm.com [9.17.195.85]) by d03relay01.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p3FINASq086294 for ; Fri, 15 Apr 2011 12:23:10 -0600 Received: from d03av05.boulder.ibm.com (loopback [127.0.0.1]) by d03av05.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p3FIN9Og009963 for ; Fri, 15 Apr 2011 12:23:10 -0600 From: Badari Pulavarty In-Reply-To: <4DA889CF.7070706@codemonkey.ws> References: <1302874855-14736-1-git-send-email-stefanha@linux.vnet.ibm.com> <20110415150513.GA29619@lst.de> <20110415153448.GA30116@lst.de> <1302884634.32391.3.camel@badari-desktop> <4DA889CF.7070706@codemonkey.ws> Content-Type: text/plain Date: Fri, 15 Apr 2011 11:25:37 -0700 Message-Id: <1302891937.32391.15.camel@badari-desktop> Mime-Version: 1.0 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: Anthony Liguori Cc: Kevin Wolf , Anthony Liguori , Stefan Hajnoczi , Stefan Hajnoczi , qemu-devel@nongnu.org, Khoa Huynh , Christoph Hellwig On Fri, 2011-04-15 at 13:09 -0500, Anthony Liguori wrote: > On 04/15/2011 11:23 AM, Badari Pulavarty wrote: > > On Fri, 2011-04-15 at 17:34 +0200, 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. > > True. That brings up a different question - whether we are doing > > enough testing on mainline QEMU :( > > The issue here is NFS, not QEMU. Sure. But we should have caught the regression on NFS when preadv/pwritev change went into QEMU or before going in -- Isn't it ? Since it was 2 years ago (like hch indicated) - we could have fixed NFS long ago :) > Moreover, the real problem is that > we're using O_DIRECT. O_DIRECT seems to result in nothing but problems > and it never seems to be tested well on any file system. O_DIRECT was added for a specific use-case in mind - and its supposed to handle only that case well (pre-allocated files with database usage - where db has their own caching layer). That case is well tested by various DB vendors on most (important) local filesystems. You know very well why we are on O_DIRECT path :) > > I think the fundamental problem we keep running into really boils down > to O_DIRECT being a second class interface within Linux. Its by design. Its a special case for specific use. Thanks, Badari