From: Tim Chen Subject: Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent cache Date: Fri, 13 Apr 2012 12:26:53 -0700 Message-ID: <1334345213.3796.21.camel@schen9-DESK> References: <20120324031357.GA5690@tassilo.jf.intel.com> <4F70F51F.8030405@linux.intel.com> <20120326235707.GC19489@thunk.org> <1334339612.3796.2.camel@schen9-DESK> <1334341876.3796.8.camel@schen9-DESK> <20120413183722.GG26332@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Linus Torvalds , Andi Kleen , Vivek Haldar , Andreas Dilger , linux-ext4@vger.kernel.org To: Ted Ts'o Return-path: Received: from mga09.intel.com ([134.134.136.24]:39245 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754050Ab2DMT0w (ORCPT ); Fri, 13 Apr 2012 15:26:52 -0400 In-Reply-To: <20120413183722.GG26332@thunk.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, 2012-04-13 at 14:37 -0400, Ted Ts'o wrote: > On Fri, Apr 13, 2012 at 11:31:16AM -0700, Tim Chen wrote: > > > > Benchmark is working on files on normal hard disk. > > However, I have I have a large number > > of processes (80 processes, one for each cpu), each reading > > a separate mmaped file. The files are in the same directory. > > That makes cache line bouncing on the counters particularly bad > > due to the large number of processes running. > > OK, so this is with an 80 CPU machine? > > And when you say 20% speed up, do you mean to say we are actually > being CPU constrained when reading from files on a normal hard disk? > The files are sparse files. So the amount of IO is limited and we are not IO constrained. Tim