From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=50682 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OF0zJ-0000Lt-Eb for qemu-devel@nongnu.org; Thu, 20 May 2010 04:20:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OF0zH-0001z9-Jm for qemu-devel@nongnu.org; Thu, 20 May 2010 04:20:17 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56732) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OF0zH-0001z1-Bi for qemu-devel@nongnu.org; Thu, 20 May 2010 04:20:15 -0400 Message-ID: <4BF4F0A4.3010304@redhat.com> Date: Thu, 20 May 2010 10:19:48 +0200 From: Kevin Wolf MIME-Version: 1.0 Subject: Re: [Qemu-devel] Re: [PATCH] block: fix sector comparism in multiwrite_req_compare References: <20100519185309.GA27591@lst.de> <20100519193802.GA29104@lst.de> <4BF43F30.4050109@msgid.tls.msk.ru> <201005192309.08252@kevin-wolf.de> <4BF4D208.2090507@redhat.com> In-Reply-To: <4BF4D208.2090507@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Kevin Wolf , Michael Tokarev , qemu-devel@nongnu.org, Christoph Hellwig Am 20.05.2010 08:09, schrieb Avi Kivity: > On 05/20/2010 12:09 AM, Kevin Wolf wrote: >> >>> Actually it's not that obvious. If the actual problem >>> here (besides the mis-comparison) is due to missing >>> barriers or flushes. Avi asked a good question in that >>> thread. >>> >> It's obvious that it's a hack. It doesn't fix anything, it just disables a >> feature that didn't work. Good for debugging, but not something that you >> would like to commit. >> >> It's reasonable to include something like this when we know that something is >> broken but we haven't found it yet - but I believe Christoph's patch is the >> real fix. If anyone can still find a case that is "fixed" by Avi's patch, I >> could be convinced to apply it anyway, but I'd prefer if I didn't have to. >> >> Note that we actually don't have overlapping requests. It just looks like it >> because the qsort call doesn't work correctly with the broken comparison >> function, so lower sector numbers can come after higher ones. >> > > I agree my patch didn't fix the problem, only made it disappear, but > won't the current code break with overlapping requests? Maybe --verbose for your patch descriptions would help. I didn't see any obvious problem. If you know any, care to explain? Anyway, I started to implement a multiwrite command for qemu-io yesterday, so that I can actually test such scenarios. Kevin