Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752360AbbEHB15 (ORCPT ); Thu, 7 May 2015 21:27:57 -0400 Received: from mail.efficios.com ([78.47.125.74]:49658 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751381AbbEHB14 (ORCPT ); Thu, 7 May 2015 21:27:56 -0400 Date: Fri, 8 May 2015 01:27:56 +0000 (UTC) From: Mathieu Desnoyers To: Steven Rostedt Cc: Drew Richardson , Peter Zijlstra , Ingo Molnar , linux-kernel@vger.kernel.org, Thomas Gleixner , John Stultz , Wade Cherry , Pawel Moll Message-ID: <1434206731.45802.1431048476130.JavaMail.zimbra@efficios.com> In-Reply-To: <20150507204228.0cb8b55c@grimm.local.home> References: <1430750469-16428-1-git-send-email-drew.richardson@arm.com> <199091314.42407.1430752205090.JavaMail.zimbra@efficios.com> <20150504200515.GA24626@dreric01-Precision-T1650> <20150504205748.GB21418@twins.programming.kicks-ass.net> <20150505145438.GA5145@dreric01-Precision-T1650> <20150507204228.0cb8b55c@grimm.local.home> Subject: Re: [PATCH] ftrace: Provide trace clock monotonic raw MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [192.222.176.50] X-Mailer: Zimbra 8.0.7_GA_6021 (ZimbraWebClient - FF37 (Linux)/8.0.7_GA_6021) Thread-Topic: ftrace: Provide trace clock monotonic raw Thread-Index: 2l5i7vTF4GlkPD4XWKuJvdfTchwTEQ== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1852 Lines: 45 ----- Original Message ----- > On Tue, 5 May 2015 07:54:46 -0700 > Drew Richardson wrote: > > > CLOCK_MONOTONIC_RAW will advance more constantly than CLOCK_MONOTONIC. > > > > Imagine someone is trying to optimize a particular program to reduce > > instructions executed for a given workload while minimizing the effect > > on runtime. Also suppose that ntp is running and potentially making > > larger adjustments to CLOCK_MONOTONIC. If ntp is adjusting > > CLOCK_MONOTONIC to advance more rapidly, the program will appear to > > use fewer instructions per second but run longer than it would if > > CLOCK_MONOTONIC_RAW had been used. The total number of instructions > > observed would be the same regardless of the clock source used, but > > how it's attributed to time would be affected. > > > > Conversely if ntp is adjusting CLOCK_MONOTONIC to advance more slowly, > > the program will appear to use more instructions per second but run > > more quickly. Of course there are many sources that can cause jitter > > in performance measurements on modern processors, but I'd like to > > remove ntp from the list. > > What's the consensus on this patch? Everyone OK with it? If so, can you > please post a new patch with the proper change log. And can everyone > else give acks. I can take it in my tree. I can see it being useful for tracing early boot, e.g. when debugging issues with NTP. So adding it to ftrace makes sense to me. Acked-by: Mathieu Desnoyers Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com -- 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/