From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750967AbZBNJPW (ORCPT ); Sat, 14 Feb 2009 04:15:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750832AbZBNJPE (ORCPT ); Sat, 14 Feb 2009 04:15:04 -0500 Received: from one.firstfloor.org ([213.235.205.2]:43146 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750792AbZBNJPB (ORCPT ); Sat, 14 Feb 2009 04:15:01 -0500 Date: Sat, 14 Feb 2009 10:32:13 +0100 From: Andi Kleen To: Mat Cc: Andi Kleen , agk@redhat.com, Linux Kernel Subject: Re: Fwd: [PATCH] Implement barrier support for single device DM devices Message-ID: <20090214093213.GC26292@one.firstfloor.org> References: <20080911174657.GN7714@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 14, 2009 at 12:26:05AM +0100, Mat wrote: > Hi Andi, > > any news on this patch ? It's in mainline as of 2.6.29-rc4. > from what I saw it isn't included in mainline yet, if it is already > please point to the kernel-config option where to enable it It's always enabled for simple DM remapped devices given that its conditions (only single underlying device etc.) are true. > heavy flush, write operations; especially on amd64/X64: > http://forums.gentoo.org/viewtopic-t-482731.html > > I'm not sure if it's possible but I believe it could also be related > to filesystems switching to synchronous writes (non-barrier > write-mode) when the underlying partition is a LUKS-partition and Note that my patch doesn't enable barriers for LUKS/dm_crypt, that would be another patch which is not currently submtted. > therefore > decreasing performance (I'm not a kernel-hacker so I don't know if > there's a possible correlation here) You can find out by testing it without LUKS, but enabling/disabling barriers on a file system and see how much difference it makes. That would be better than speculating. > > some factors I noticed having an impact on that are: How did you determine that? Did you run some repeatable benchmark that gave different numbers? > - the i/o scheduler hardly makes a change > - elder boxes with PCI (non-PCIe) can be "fixed" with some latency-tweaks: > setpci -v -d *:* latency_timer=b0 You realize that the PCI latency has nothing to do with IO scheduler delays? It's very unlikely that there is a correlation there. Please double check these results. -Andi -- ak@linux.intel.com -- Speaking for myself only.