Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751890AbbBVIWe (ORCPT ); Sun, 22 Feb 2015 03:22:34 -0500 Received: from mail-wi0-f180.google.com ([209.85.212.180]:51120 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751734AbbBVIWd (ORCPT ); Sun, 22 Feb 2015 03:22:33 -0500 Date: Sun, 22 Feb 2015 09:22:28 +0100 From: Ingo Molnar To: Borislav Petkov Cc: Andy Lutomirski , Oleg Nesterov , Rik van Riel , x86@kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Arjan van de Ven Subject: Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs Message-ID: <20150222082228.GB22972@gmail.com> References: <20150221093150.GA27841@gmail.com> <20150221163840.GA32073@pd.tnic> <20150221172914.GB32073@pd.tnic> <20150221183952.GD8406@gmail.com> <20150221191527.GC32073@pd.tnic> <20150221192352.GA10027@gmail.com> <20150221213625.GD32073@pd.tnic> <20150222081840.GA22972@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150222081840.GA22972@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1137 Lines: 29 * Ingo Molnar wrote: > - Do you have enough RAM that there's essentially no IO > in the system worth speaking of? Do you have enough RAM > to copy a whole kernel tree to /tmp/linux/ and do the > measurement there, on ramfs? Doing that will also pin down the page cache: kernel build times are very sensitive to the page cache layout, and once a page cache layout is established on systems with lots of RAM it does not tend to be flushed out. But the next bootup will generate another random page cache layout - which makes inter-kernel kernel build times comparisons much noiser than the run-to-run numbers suggest. So to get more precise measurements a 'pinned' page cache layout and the dynamic debug switch you implemented is very helpful and --repeat stddev will be pretty representative of the true noise of the measurement. Thanks, 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/