Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762187AbZATThd (ORCPT ); Tue, 20 Jan 2009 14:37:33 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755388AbZATThY (ORCPT ); Tue, 20 Jan 2009 14:37:24 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:36953 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753292AbZATThX (ORCPT ); Tue, 20 Jan 2009 14:37:23 -0500 Date: Tue, 20 Jan 2009 20:37:03 +0100 From: Ingo Molnar To: Nick Piggin Cc: Linux Kernel Mailing List , Linus Torvalds , hpa@zytor.com, jeremy@xensource.com, chrisw@sous-sol.org, zach@vmware.com, rusty@rustcorp.com.au, Andrew Morton Subject: Re: lmbench lat_mmap slowdown with CONFIG_PARAVIRT Message-ID: <20090120193703.GA27930@elte.hu> References: <20090120110542.GE19505@wotan.suse.de> <20090120112634.GA20858@elte.hu> <20090120140324.GA26424@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090120140324.GA26424@elte.hu> 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 Content-Length: 1790 Lines: 42 * Ingo Molnar wrote: > ----------------------------------------------- > | Performance counter stats for './mmap-perf' | > ----------------------------------------------- > | | > | x86-defconfig | PARAVIRT=y > |------------------------------------------------------------------ > | > | 1311.554526 | 1360.624932 task clock ticks (msecs) +3.74% > | | > | 1 | 1 CPU migrations > | 91 | 79 context switches > | 55945 | 55943 pagefaults > | ............................................ > | 3781392474 | 3918777174 CPU cycles +3.63% > | 1957153827 | 2161280486 instructions +10.43% > | 50234816 | 51303520 cache references +2.12% > | 5428258 | 5583728 cache misses +2.86% > | | > | 1314.782469 | 1363.694447 time elapsed (msecs) +3.72% > | | > ----------------------------------- > > The most surprising element is that in the paravirt_ops case we run 204 > million more instructions - out of the ~2000 million instructions total. So because this test does exactly 1 million MM syscalls, the average is easy to calculate: The native kernel's average MM syscall cost is 1957 instructions - with CONFIG_PARAVIRT=y that increases by +10.43% to 2161 instructions. There's over 200 extra instructions executed per MM syscall that we only do due to CONFIG_PARAVIRT=y. Ingo -- 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/