Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754771AbZFIO6R (ORCPT ); Tue, 9 Jun 2009 10:58:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750998AbZFIO6C (ORCPT ); Tue, 9 Jun 2009 10:58:02 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:43469 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750725AbZFIO6B (ORCPT ); Tue, 9 Jun 2009 10:58:01 -0400 Date: Tue, 9 Jun 2009 16:57:36 +0200 From: Ingo Molnar To: Linus Torvalds Cc: Nick Piggin , Rusty Russell , Jeremy Fitzhardinge , "H. Peter Anvin" , Thomas Gleixner , Linux Kernel Mailing List , Andrew Morton , Peter Zijlstra , Avi Kivity , Arjan van de Ven Subject: Re: [benchmark] 1% performance overhead of paravirt_ops on native kernels Message-ID: <20090609145736.GA31535@elte.hu> References: <4A0B62F7.5030802@goop.org> <200906032208.28061.rusty@rustcorp.com.au> <200906041554.37102.rusty@rustcorp.com.au> <20090609093918.GC16940@wotan.suse.de> 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-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=3.2.5 -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: 831 Lines: 21 * Linus Torvalds wrote: > I was benchmarking btrfs on my little EeePC. There, kmap overhead > was 25% of file access time. Part of it is that people have been > taught to use "kmap_atomic()", which is usable under spinlocks and > people have been told that it's "fast". It's not fast. The whole > TLB thing is slow as hell. yeah. I noticed it some time ago that INVLPG is unreasonably slow. My theory is that in the CPU it's perhaps a loop (in microcode?) over _all_ TLBs - so as TLB caches get larger, INVLPG gets slower and slower ... 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/