Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932173AbaFPQfI (ORCPT ); Mon, 16 Jun 2014 12:35:08 -0400 Received: from mail-ve0-f172.google.com ([209.85.128.172]:45101 "EHLO mail-ve0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754673AbaFPQfG (ORCPT ); Mon, 16 Jun 2014 12:35:06 -0400 MIME-Version: 1.0 In-Reply-To: <539EB03C.5080100@linaro.org> References: <1401903034-20074-1-git-send-email-dianders@chromium.org> <539E0D8E.9080706@linaro.org> <539EB03C.5080100@linaro.org> Date: Mon, 16 Jun 2014 09:35:04 -0700 X-Google-Sender-Auth: 3hgrujkuyg7SAAu9GQLx7XZcUJU Message-ID: Subject: Re: [PATCH 1/3] clocksource: exynos_mct: Fix ftrace From: Doug Anderson To: Daniel Lezcano Cc: Kukjin Kim , Tomasz Figa , Vincent Guittot , Chirantan Ekbote , David Riley , Olof Johansson , linux-samsung-soc , Thomas Gleixner , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Daniel, On Mon, Jun 16, 2014 at 1:52 AM, Daniel Lezcano wrote: > Hi Dough, > > thanks for the explanation. I still don't get why it is important to keep > others users of mct traceable because it is quite slow ? May be it is what > you explained here, but I miss the connection between 'the other users' <-> > 'traceable' <-> 'because slow'. It stems from the fact that one use of trace is to figure out why things are slow. In that case you want to make sure that the slow things are traceable. I can run the following: cd /sys/kernel/debug/tracing echo nop > current_tracer echo 0 > options/sleep-time echo 0 > options/graph-time echo 1 > function_profile_enabled ~/gettimeofday 100000 echo 0 > function_profile_enabled Then I can see this: Function Hit Time Avg s^2 -------- --- ---- --- --- __getnstimeofday 100005 258267.8 us 2.582 us 447196.9 us do_gettimeofday 100004 252395.6 us 2.523 us 462549.6 us SyS_gettimeofday 100004 249353.6 us 2.493 us 1223308 us getnstimeofday 100005 246217.2 us 2.462 us 369149.8 us exynos4_frc_read 101096 181620.0 us 1.796 us 157413.8 us ...if I mark exynos4_frc_read() as notrace then it doesn't show up in the profile, which is unfortunate. NOTE: the above profile is a bit misleading in terms of actual time taken my belief is that we end up with some confusing numbers since profiling uses the MCT itself (I think) to record how long a function took to execute. Despite this it's still awfully nice that exynos4_frc_read() actually shows up in the trace... -- 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/