From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754569AbcAVRPa (ORCPT ); Fri, 22 Jan 2016 12:15:30 -0500 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:57589 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753951AbcAVRP1 (ORCPT ); Fri, 22 Jan 2016 12:15:27 -0500 Subject: Re: [BUG] Regression introduced with "block: split bios to max possible length" To: Keith Busch , Linus Torvalds References: <56A0F1CA.4010303@linux.vnet.ibm.com> <56A14EE4.1020008@fb.com> <20160121225127.GA30993@localhost.localdomain> <20160122032135.GA9244@localhost.localdomain> <20160122145559.GA21984@localhost.localdomain> CC: Stefan Haberland , Linux Kernel Mailing List , linux-s390 , Sebastian Ott From: Jens Axboe Message-ID: <56A263A7.6070406@fb.com> Date: Fri, 22 Jan 2016 10:15:19 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <20160122145559.GA21984@localhost.localdomain> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.54.13] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-01-22_06:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/22/2016 07:56 AM, Keith Busch wrote: > On Thu, Jan 21, 2016 at 08:15:37PM -0800, Linus Torvalds wrote: >> For the case of nvme, for example, I think the max sector number is so >> high that you'll never hit that anyway, and you'll only ever hit the >> chunk limit. No? > > The device's max transfer and chunk size are not very large, both fixed > at 128KB. We can lose ~70% of potential throughput when IO isn't aligned, > and end users reported this when the block layer stopped splitting on > alignment for the NVMe drive. > > So it's a big deal for this h/w, but now I feel awkward defending a > device specific feature for the generic block layer. Honestly, the splitting code is what is a piece of crap, we never should have gone down that route. Hopefully we can get rid of it soon. In the mean time, this does need to work. It's an odd hw construct (basically two devices bolted together), but it's not really an esoteric thing to support. > Anyway, the patch was developed with incorrect assumptions. I'd still > like to try again after reconciling the queue limit constraints, but > I defer to Jens for the near term. Instead of scrambling for -rc1, I'd suggest we just revert again and ensure what we merge for -rc2 is clean and passes the test cases. -- Jens Axboe