From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [Xen-devel] Re: [PATCH] xen block backend driver. - proper flush/barrier/fua support missing. Date: Mon, 2 May 2011 15:08:43 -0400 Message-ID: <20110502190843.GA29913@dumpdata.com> References: <1303333543-5915-1-git-send-email-konrad.wilk@oracle.com> <1303333543-5915-2-git-send-email-konrad.wilk@oracle.com> <20110421034016.GB11501@infradead.org> <1303412592.9571.126.camel@agari.van.xensource.com> <20110421190606.GA10793@infradead.org> <1303413277.9571.133.camel@agari.van.xensource.com> <20110422090904.GA29246@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20110422090904.GA29246@infradead.org> Sender: linux-kernel-owner@vger.kernel.org To: Christoph Hellwig Cc: Daniel Stodden , "xen-devel@lists.xensource.com" , "jaxboe@fusionio.com" , "linux-kernel@vger.kernel.org" , "konrad@kernel.org" List-Id: xen-devel@lists.xenproject.org On Fri, Apr 22, 2011 at 05:09:04AM -0400, Christoph Hellwig wrote: > On Thu, Apr 21, 2011 at 12:14:37PM -0700, Daniel Stodden wrote: > > > There is a huge userbase of guests out there that does rely on it. > > > > Which ones? Old blkfront would have make a difference back then when > > barriers used to be an option, but it never actually declared it, right? > > Pre-Linux 2.6.37 guests using reiserfs actually relied on the queue > flushing. This includes a lot of SLES installation which are still > in common use. There's only two options to make sure they work: > > (1) keep the original barrier semantics and flush the queue > (2) do not advertize "barrier" support at all, and make sure to submit > every I/O we get with the FUA bit. > > In practice (2) is going to be faster for most real-life workloads. So > maybe you should just drop the old "barrier" support and just send > requests with the FUA bit set for now, until you have proper flush > and fua support in the protocol. Let me play with both options and see how they pan out. Christoph, Is there a good tool to unmask barrier bugs? I found this one: http://lwn.net/Articles/283169/ but not sure if that still applies to this case? Or does running bonnie++ expose the potential issues?