Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756232AbZFHOzK (ORCPT ); Mon, 8 Jun 2009 10:55:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754961AbZFHOzA (ORCPT ); Mon, 8 Jun 2009 10:55:00 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:54443 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754633AbZFHOzA (ORCPT ); Mon, 8 Jun 2009 10:55:00 -0400 Date: Mon, 8 Jun 2009 07:53:29 -0700 (PDT) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Rusty Russell cc: Ingo Molnar , Nick Piggin , Jeremy Fitzhardinge , "H. Peter Anvin" , Thomas Gleixner , Linux Kernel Mailing List , Andrew Morton , Peter Zijlstra , Avi Kivity , Arjan van de Ven , Gerd Knorr Subject: Re: [benchmark] 1% performance overhead of paravirt_ops on native kernels In-Reply-To: <200906071023.04789.rusty@rustcorp.com.au> Message-ID: References: <4A0B62F7.5030802@goop.org> <200906051416.19311.rusty@rustcorp.com.au> <200906071023.04789.rusty@rustcorp.com.au> User-Agent: Alpine 2.01 (LFD 1184 2008-12-16) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1061 Lines: 29 On Sun, 7 Jun 2009, Rusty Russell wrote: > > "possible"? You mean "acceptable". Gray, not black and white. I don't think we can possibly claim to support UP configurations if we don't patch. > 1) Where's the line? "As good as we can make it". There is no line. There's "your code sucks so badly that it needs to get fixed, or we'll rip it out or disable it". > 2) Where are we? Does patching claw back 5% of the loss? 50%? 90%? On some things, especially on P4, the lock overhead was tens of percent. Just a single locked instruction takes closer to two hundred instructions. Of course, on those P4's, just kernel entry/exit is pretty high too (even with sysenter/exit), so I doubt you'll ever see something be 90% just because of that, unless it causes extra IO or other non-CPU issues. Linus -- 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/