From: Tim Chen Subject: Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent cache Date: Fri, 13 Apr 2012 11:31:16 -0700 Message-ID: <1334341876.3796.8.camel@schen9-DESK> References: <20120323221715.GA6712@tassilo.jf.intel.com> <20120324031357.GA5690@tassilo.jf.intel.com> <4F70F51F.8030405@linux.intel.com> <20120326235707.GC19489@thunk.org> <1334339612.3796.2.camel@schen9-DESK> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Andi Kleen , Ted Ts'o , Vivek Haldar , Andreas Dilger , linux-ext4@vger.kernel.org To: Linus Torvalds Return-path: Received: from mga09.intel.com ([134.134.136.24]:54503 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755853Ab2DMSbQ (ORCPT ); Fri, 13 Apr 2012 14:31:16 -0400 In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On Fri, 2012-04-13 at 11:08 -0700, Linus Torvalds wrote: > On Fri, Apr 13, 2012 at 10:53 AM, Tim Chen wrote: > >> > >> Do you have numbers? > > > > In a benchmark that does mmaped-read, there is a 28% speed up > > after getting rid of the counters. > > Ok, that's big. But is it any actual real workload on a real > filesystem? It looks like this should only happen for actual IO, so I > get the feeling that this is some made-up benchmark for a filesystem > on a RAM-disk? > > Linus 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. Tim