Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753192AbcD2JYA (ORCPT ); Fri, 29 Apr 2016 05:24:00 -0400 Received: from ofcsgdbm.dwd.de ([141.38.3.245]:41811 "EHLO ofcsgdbm.dwd.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753037AbcD2JX5 (ORCPT ); Fri, 29 Apr 2016 05:23:57 -0400 Date: Fri, 29 Apr 2016 09:23:54 +0000 (UTC) From: Holger Kiehl X-X-Sender: kiehl@diagnostix.dwd.de To: Shaohua Li cc: linux-block@vger.kernel.org, linux-kernel , linux-raid , qkrwngud825@gmail.com, Kernel-team@fb.com, Ming Lei , Jens Axboe , Neil Brown Subject: Re: [PATCH] MD: make bio mergeable In-Reply-To: <20160428211908.GA3116523@devbig084.prn1.facebook.com> Message-ID: References: <384a0e0c7d6f2700aadbcbdef003cece88fa7dd7.1461626533.git.shli@fb.com> <20160428211908.GA3116523@devbig084.prn1.facebook.com> User-Agent: Alpine 2.20 (LRH 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1425 Lines: 38 On Thu, 28 Apr 2016, Shaohua Li wrote: > On Thu, Apr 28, 2016 at 08:00:22PM +0000, Holger Kiehl wrote: > > Hello, > > > > On Mon, 25 Apr 2016, Shaohua Li wrote: > > > > > blk_queue_split marks bio unmergeable, which makes sense for normal bio. > > > But if dispatching the bio to underlayer disk, the blk_queue_split > > > checks are invalid, hence it's possible the bio becomes mergeable. > > > > > > In the reported bug, this bug causes trim against raid0 performance slash > > > https://bugzilla.kernel.org/show_bug.cgi?id=117051 > > > > > This patch makes a huge difference. On a system with two Samsung 850 Pro > > in a MD Raid0 setup the time for fstrim went down from ~30min to 18sec! > > > > However, on another system with two Intel P3700 1.6TB NVMe PCIe SSD's > > also setup as one big MD Raid0, the patch does not make any difference > > at all. fstrim takes more then 4 hours! > > Does the raid0 cross two partitions or two SSD? > Two SSD's. Where it works, for the two Samsung 850 Pro SATA SSD it was via partitions. > can you post blktrace data in the bugzilloa, I'll track the bug there. > I did the blktrace on the two md raid0 devices /dev/nvme[01]n1 for 2 minutes and attached them to the bug 117051 as a tar.bz2 file: https://bugzilla.kernel.org/show_bug.cgi?id=117051 Please just ask if I have forgotten anything. And many thanks for looking at this and all the good work! Regards, Holger