Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752510AbbEDUF1 (ORCPT ); Mon, 4 May 2015 16:05:27 -0400 Received: from foss.arm.com ([217.140.101.70]:43367 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752278AbbEDUFW (ORCPT ); Mon, 4 May 2015 16:05:22 -0400 Date: Mon, 4 May 2015 13:05:19 -0700 From: Drew Richardson To: Mathieu Desnoyers Cc: Steven Rostedt , Ingo Molnar , "linux-kernel@vger.kernel.org" , Thomas Gleixner , Peter Zijlstra , John Stultz , Wade Cherry , Pawel Moll Subject: Re: [PATCH] ftrace: Provide trace clock monotonic raw Message-ID: <20150504200515.GA24626@dreric01-Precision-T1650> References: <1430750469-16428-1-git-send-email-drew.richardson@arm.com> <199091314.42407.1430752205090.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <199091314.42407.1430752205090.JavaMail.zimbra@efficios.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: 2048 Lines: 68 On Mon, May 04, 2015 at 04:10:05PM +0100, Mathieu Desnoyers wrote: > ----- Original Message ----- > > Expose the NMI safe accessor to the monotonic raw clock to the > > tracer. The mono clock was added with commit > > 1b3e5c0936046e7e023149ddc8946d21c2ea20eb. Although the monotonic raw > > clock cannot be used to compare time between different machines, it is > > not perterbed by ntp. > > perterbed -> perturbed Oops, I'll correct that in the next version. > > > > Signed-off-by: Drew Richardson > > > > What is the use-case that justify exposing the "raw fast" > clock that cannot be handled by the "monotonic fast" clock ? > > Thanks, > > Mathieu I'm collecting and merging data from perf, with Android Atrace data (writes to /sys/kernel/debug/tracing/trace_marker) which ends up in the ftrace stream and other measurements collected from userspace. Currently the only clock readable from userspace, supported by perf and by ftrace is CLOCK_MONOTONIC. However this clock is affected by the incremental adjustments performed by adjtime(3) and NTP. But I'd prefer to use a clock that is advancing at a consistent rate, hence CLOCK_MONOTONIC_RAW. Thanks, Drew > > --- > > kernel/trace/trace.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > > index 05330494a0df..458031c31a37 100644 > > --- a/kernel/trace/trace.c > > +++ b/kernel/trace/trace.c > > @@ -876,6 +876,7 @@ static struct { > > { trace_clock_jiffies, "uptime", 0 }, > > { trace_clock, "perf", 1 }, > > { ktime_get_mono_fast_ns, "mono", 1 }, > > + { ktime_get_raw_fast_ns, "mono_raw", 1 }, > > ARCH_TRACE_CLOCKS > > }; > > > > -- > > 2.1.4 > > > > > > -- > 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/