Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751743AbbEFEwq (ORCPT ); Wed, 6 May 2015 00:52:46 -0400 Received: from mail-wi0-f195.google.com ([209.85.212.195]:35083 "EHLO mail-wi0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750812AbbEFEwn (ORCPT ); Wed, 6 May 2015 00:52:43 -0400 From: Ingo Molnar X-Google-Original-From: Ingo Molnar Date: Wed, 6 May 2015 06:52:39 +0200 To: Andy Lutomirski Cc: Borislav Petkov , Fenghua Yu , Thomas Gleixner , Dave Hansen , Linus Torvalds , Oleg Nesterov , "H. Peter Anvin" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 207/208] x86/fpu: Add FPU performance measurement subsystem Message-ID: <20150506045239.GA12393@gmail.com> References: <1430848712-28064-1-git-send-email-mingo@kernel.org> <1430848712-28064-47-git-send-email-mingo@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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: 1384 Lines: 38 * Andy Lutomirski wrote: > On May 5, 2015 11:30 PM, "Ingo Molnar" wrote: > > > > Add a short FPU performance suite that runs once during bootup. > > > > It can be enabled via CONFIG_X86_DEBUG_FPU_PERFORMANCE=y. > > Neat! > > Can you change "cycles" to "TSC ticks"? They're not quite the same thing. Yeah, with constant TSC we have the magic TSC frequency that is used by RDTSC. I'm torn: 'TSC ticks' will mean very little to most people reading that output. We could convert it to nsecs with a little bit of calibration - but that makes it depend on small differences in CPU model frequencies, while the (cached) cycle costs are typically constant per microarchitecture. I suspect we could snatch a performance counter temporarily, to get the real cycles count, and maybe even add a uops column. Most of this needs to run in kernel space, so it's not a tooling project. I also wanted to add cache-cold numbers which are very interesting as well, just awfully hard to measure in a stable fashion. For cache-cold numbers the natural unit would be memory bus cycles. 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/