Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751980AbbBUTQc (ORCPT ); Sat, 21 Feb 2015 14:16:32 -0500 Received: from mail.skyhub.de ([78.46.96.112]:45120 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751857AbbBUTQb (ORCPT ); Sat, 21 Feb 2015 14:16:31 -0500 Date: Sat, 21 Feb 2015 20:15:27 +0100 From: Borislav Petkov To: Ingo Molnar Cc: Andy Lutomirski , Oleg Nesterov , Rik van Riel , x86@kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds Subject: Re: [RFC PATCH] x86, fpu: Use eagerfpu by default on all CPUs Message-ID: <20150221191527.GC32073@pd.tnic> References: <20150221093150.GA27841@gmail.com> <20150221163840.GA32073@pd.tnic> <20150221172914.GB32073@pd.tnic> <20150221183952.GD8406@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20150221183952.GD8406@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: 1335 Lines: 37 On Sat, Feb 21, 2015 at 07:39:52PM +0100, Ingo Molnar wrote: > So the workload improved by ~600,000 usecs, and there's > 68,000 less calls, so it saved 8.8 usecs per call. Isn't I think you mean more calls. The eager measurement has more calls. Let me do some primitive math: def =(234.681331200 / 712000)*10^6 = 329.60861123595505000000 microsecs/call eager=(234.066525648 / 780000)*10^6 = 300.08528929230769000000 microsecs/call diff is 29.52332194364736000000 microsecs speedup per call which could explain the cost of CR0.TS serialization semantics in the lazy mode. > that a bit too high? Now, is 29 microseconds too high? I'm not sure this is even correct and not some noise interfering. > I'd sleep a lot better if we had some runtime debug flag to > be able to do run-to-run comparisons on the same booted up > kernel, or so. Let me take a look whether we could so some knob... The nice thing is, code uses use_eager_fpu() to check stuff so we should be able to clear the cpufeature flag. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- -- 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/