From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from h19-45-4-185.rev.hosting.nbs-system.com ([185.4.45.19]:23890 "EHLO owa.groupeot.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751182AbdHBQ35 (ORCPT ); Wed, 2 Aug 2017 12:29:57 -0400 Subject: Re: [Xen-users] File-based domU - Slow storage write since xen 4.8 To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= CC: Keith Busch , , , WebDawg References: <20170720085256.e3m35aalg6jn7qrh@dhcp-3-128.uk.xensource.com> <7205d904-44a3-631f-fbd8-8b62d43ca4e0@nbs-system.com> <20170720173606.GD1202@localhost.localdomain> <3443d6ac-9011-85fb-3613-bacdee184fcc@nbs-system.com> <20170721155333.GG1202@localhost.localdomain> <20170721160712.74ee5f3xztbecanw@dhcp-3-128.uk.xensource.com> <6d76c489-1f1a-205f-434d-8fa1a486d2c4@nbs-system.com> <20170725222505.GH11979@localhost.localdomain> <1642cf06-d9a3-1037-e3c9-6b6b3fc9db2d@nbs-system.com> <20170801094831.cr2brqudqubcinxt@dhcp-3-128.uk.xensource.com> From: Benoit Depail Message-ID: <46b4bdb3-25c4-076e-3401-0506688e2d83@nbs-system.com> Date: Wed, 2 Aug 2017 18:29:48 +0200 MIME-Version: 1.0 In-Reply-To: <20170801094831.cr2brqudqubcinxt@dhcp-3-128.uk.xensource.com> Content-Type: text/plain; charset="utf-8" Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On 08/01/2017 11:48 AM, Roger Pau Monné wrote: > On Fri, Jul 28, 2017 at 04:50:27PM +0200, Benoit Depail wrote: >> On 07/26/17 00:25, Keith Busch wrote: >>> On Fri, Jul 21, 2017 at 07:07:06PM +0200, Benoit Depail wrote: >>>> On 07/21/17 18:07, Roger Pau Monné wrote: >>>>> >>>>> Hm, I'm not sure I follow either. AFAIK this problem came from >>>>> changing the Linux version in the Dom0 (where the backend, blkback is >>>>> running), rather than in the DomU right? >>>>> >>>>> Regarding the queue/sectors stuff, blkfront uses several blk_queue >>>>> functions to set those parameters, maybe there's something wrong >>>>> there, but I cannot really spot what it is: >>>>> >>>>> http://elixir.free-electrons.com/linux/latest/source/drivers/block/xen-blkfront.c#L929 >>>>> >>>>> In the past the number of pages that could fit in a single ring >>>>> request was limited to 11, but some time ago indirect descriptors >>>>> where introduced in order to lift this limit, and now requests can >>>>> have a much bigger number of pages. >>>>> >>>>> Could you check the max_sectors_kb of the underlying storage you are >>>>> using in Dom0? >>>>> >>>>> Roger. >>>>> >>>> I checked the value for the loop device as well >>>> >>>> With 4.4.77 (bad write performance) >>>> $ cat /sys/block/sda/queue/max_sectors_kb >>>> 1280 >>>> $ cat /sys/block/loop1/queue/max_sectors_kb >>>> 127 >>>> >>>> >>>> With 4.1.42 (normal write performance) >>>> $ cat /sys/block/sda/queue/max_sectors_kb >>>> 4096 >>>> $ cat /sys/block/loop1/queue/max_sectors_kb >>>> 127 >>> >>> Thank you for the confirmations so far. Could you confirm performance dom0 >>> running 4.4.77 with domU running 4.1.42, and the other way around? Would >>> like to verify if this is just isolated to blkfront. >>> >> Hi, >> >> I've ran the tests, and I can tell that the domU kernel version have no >> influence on the performance. >> >> Dom0 with 4.4.77 always shows bad performance, wether the domU runs >> 4.1.42 or 4.4.77. >> >> Dom0 with 4.1.42 always shows good performance, wether the domU runs >> 4.1.42 or 4.4.77. > > Hello, > > I haven't yet got time to look into this sadly. Can you please try to > use fio [0] in order to run the tests against the loop device in Dom0? > > If possible, could you test several combinations of block sizes, I/O > sizes and I/O depths? > > Thanks, Roger. > > [0] http://git.kernel.dk/?p=fio.git;a=summary > Ok I'll give a try later when I have more time. Probably next week. Thanks, -- Benoit Depail Senior Infrastructures Architect NBS System