Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754467AbZFDVxS (ORCPT ); Thu, 4 Jun 2009 17:53:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751447AbZFDVxG (ORCPT ); Thu, 4 Jun 2009 17:53:06 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.125]:39939 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751060AbZFDVxF (ORCPT ); Thu, 4 Jun 2009 17:53:05 -0400 From: Dave McCracken To: Linus Torvalds Subject: Re: [benchmark] 1% performance overhead of paravirt_ops on native kernels Date: Thu, 4 Jun 2009 16:52:54 -0500 User-Agent: KMail/1.11.2 (Linux/2.6.28; KDE/4.2.2; x86_64; ; ) Cc: Rusty Russell , 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 References: <4A0B62F7.5030802@goop.org> <200906041554.37102.rusty@rustcorp.com.au> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200906041652.55298.dcm@mccr.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1810 Lines: 38 On Thursday 04 June 2009, Linus Torvalds wrote: > On Thu, 4 Jun 2009, Rusty Russell wrote: > > > Turn off HIGHMEM64G, please (and HIGHMEM4G too, for that matter - you > > > can't compare it to a no-highmem case). > > > > Thanks, your point is demonstrated below. I don't think HIGHMEM4G is > > unreasonable for a distro tho, so I turned that on instead. > > Well, I agree that HIGHMEM4G is a reasonable thing to turn on. > > The thing I disagree with is that it's at all valid to then compare to > some all-software feature thing. HIGHMEM doesn't expand any esoteric > capability that some people might use - it's about regular RAM for regular > users. I think you're missing the point of Rusty's benchmark. I see his exercise as "compare a kernel configured as a distro would vs a custom-built kernel configured for the exact target environment". In that light, questions about the CONFIG options Rusty used should be based on whether most distros would use them in their stock kernels as opposed to how necessary they are. What I see as the message of his benchmark is if you care about performance you should be customizing your kernel anyway. Distro kernels are slow. An option that makes the distro kernel a bit slower is no big deal since anyone who wants speed should already be rebuilding their kernel. Don't get me wrong. I think it's always a good idea to minimize any performance penalty, even under specific configurations. I just think criticizing it because distros might enable it is a poor argument. Dave McCracken Oracle Corp. -- 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/