Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754600AbYHHILN (ORCPT ); Fri, 8 Aug 2008 04:11:13 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752783AbYHHILA (ORCPT ); Fri, 8 Aug 2008 04:11:00 -0400 Received: from serv2.oss.ntt.co.jp ([222.151.198.100]:33145 "EHLO serv2.oss.ntt.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751091AbYHHIK7 (ORCPT ); Fri, 8 Aug 2008 04:10:59 -0400 Subject: Re: RFC: I/O bandwidth controller From: Fernando Luis =?ISO-8859-1?Q?V=E1zquez?= Cao To: Ryo Tsuruta Cc: taka@valinux.co.jp, dave@linux.vnet.ibm.com, yoshikawa.takuya@oss.ntt.co.jp, uchida@ap.jp.nec.com, ngupta@google.com, linux-kernel@vger.kernel.org, dm-devel@redhat.com, containers@lists.linux-foundation.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xensource.com, agk@sourceware.org, righi.andrea@gmail.com In-Reply-To: <20080808.162024.189720323.ryov@valinux.co.jp> References: <1217870433.20260.101.camel@nimitz> <1217985189.3154.57.camel@sebastian.kern.oss.ntt.co.jp> <20080808.152119.43521725.taka@valinux.co.jp> <20080808.162024.189720323.ryov@valinux.co.jp> Content-Type: text/plain Organization: NTT Open Source Software Center Date: Fri, 08 Aug 2008 17:10:56 +0900 Message-Id: <1218183056.17648.6.camel@sebastian.kern.oss.ntt.co.jp> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1888 Lines: 40 On Fri, 2008-08-08 at 16:20 +0900, Ryo Tsuruta wrote: > > > - Implement a block layer resource controller. dm-ioband is a working > > > solution and feature rich but its dependency on the dm infrastructure is > > > likely to find opposition (the dm layer does not handle barriers > > > properly and the maximum size of I/O requests can be limited in some > > > cases). In such a case, we could either try to build a standalone > > > resource controller based on dm-ioband (which would probably hook into > > > generic_make_request) or try to come up with something new. > > > > I doubt about the maximum size of I/O requests problem. You can't avoid > > this problem as far as you use device mapper modules with such a bad > > manner, even if the controller is implemented as a stand-alone controller. > > There is no limitation if you only use dm-ioband without any other device > > mapper modules. > > The following is a part of source code where the limitation comes from. > > dm-table.c: dm_set_device_limits() > /* > * Check if merge fn is supported. > * If not we'll force DM to use PAGE_SIZE or > * smaller I/O, just to be safe. > */ > > if (q->merge_bvec_fn && !ti->type->merge) > rs->max_sectors = > min_not_zero(rs->max_sectors, > (unsigned int) (PAGE_SIZE >> 9)); > > As far as I can find, In 2.6.27-rc1-mm1, Only some software RAID > drivers and pktcdvd driver define merge_bvec_fn(). Yup, exactly. The implication of this is that we may see a drop in performance in some RAID configurations. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/