From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759279AbYHONqg (ORCPT ); Fri, 15 Aug 2008 09:46:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758481AbYHONqO (ORCPT ); Fri, 15 Aug 2008 09:46:14 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:49607 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758282AbYHONqN (ORCPT ); Fri, 15 Aug 2008 09:46:13 -0400 Date: Fri, 15 Aug 2008 15:45:45 +0200 From: Ingo Molnar To: Hugh Dickins Cc: Andi Kleen , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86: fix /proc/meminfo DirectMap Message-ID: <20080815134545.GB9243@elte.hu> References: <20080815131530.GG19125@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Hugh Dickins wrote: > On Fri, 15 Aug 2008, Andi Kleen wrote: > > On Fri, Aug 15, 2008 at 01:58:32PM +0100, Hugh Dickins wrote: > > > Do we actually want these DirectMap lines in the x86 /proc/meminfo? > > > I can see they're interesting to CPA developers and TLB optimizers, > > > but they don't fit its usual "where has all my memory gone?" usage. > > > > It was intended for the "why is my computer going slower" usage. > > Yes, that's what I meant by the TLB optimizers. But it's going to be > a fractional effect, isn't it, when you're trying to get the last 1% > out of the machine? And in such a case, you might wonder more what > all the 4k ones are actually being used for (no problem at all if > they've ended up behind vmalloced module text). i cannot see any performance difference myself between 2MB and 1GB TLBs. There are measurements that Andi Kleen did originally in this commit: commit 8346ea17aa20e9864b0f7dc03d55f3cd5620b8c1 Author: Andi Kleen Date: Wed Mar 12 03:53:32 2008 +0100 x86: split large page mapping for AMD TSEG [lower is better] no split stddev split stddev delta Elapsed Time 87.146 (0.727516) 84.296 (1.09098) -3.2% User Time 274.537 (4.05226) 273.692 (3.34344) -0.3% System Time 34.907 (0.42492) 34.508 (0.26832) -1.1% Percent CPU 322.5 (38.3007) 326.5 (44.5128) +1.2% => About 3.2% improvement in elapsed time for kernbench. [...] meanwhile i have Barcelona class hardware myself and i cannot reproduce these claimed improvements in kernbench performance. gbpages versus no-gbpages results are dead on the same, within statistical noise. ( i'm sure it could make some difference in synthetic user-space workloads - but gbpages are not exposed to user-space anyway. ) Ingo