Re: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset latency

Path	csiph.com!1.us.feeder.erje.net!feeder.erje.net!2.eu.feeder.erje.net!news2.arglkargh.de!news.mixmin.net!aioe.org!bofh.it!news.nic.it!robomod
From	Thomas Gleixner <tglx@linutronix.de>
Newsgroups	linux.kernel
Subject	Re: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset latency
Date	Thu, 22 Sep 2016 19:40:03 +0200
Message-ID	<skg8z-Rq-81@gated-at.bofh.it> (permalink)
References	<sjtKx-3DJ-3@gated-at.bofh.it> <sjtKx-3DJ-5@gated-at.bofh.it> <sjudA-46X-9@gated-at.bofh.it> <sjITg-5i1-5@gated-at.bofh.it> <sjSfU-2IV-17@gated-at.bofh.it> <sk8kF-4r1-13@gated-at.bofh.it>
X-Original-To	Binoy Jayan <binoy.jayan@linaro.org>
User-Agent	Alpine 2.20 (DEB 67 2015-01-07)
MIME-Version	1.0
Content-Type	text/plain; charset=US-ASCII
Sender	robomod@news.nic.it
List-ID	<linux-kernel.vger.kernel.org>
X-Mailing-List	linux-kernel@vger.kernel.org
Approved	robomod@news.nic.it
Lines	36
Organization	linux.* mail to news gateway
X-Original-Cc	Carsten Emde <C.Emde@osadl.org>, "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>, Daniel Wagner <daniel.wagner@bmw-carit.de>, Arnd Bergmann <arnd@arndb.de>, Linux kernel mailing list <linux-kernel@vger.kernel.org>, Masami <masami.hiramatsu@linaro.org>, Mark Brown <mark.brown@linaro.org>
X-Original-Date	Thu, 22 Sep 2016 19:28:01 +0200 (CEST)
X-Original-Message-ID	<alpine.DEB.2.20.1609221910060.5599@nanos>
X-Original-References	<1474379517-7705-1-git-send-email-binoy.jayan@linaro.org> <1474379517-7705-5-git-send-email-binoy.jayan@linaro.org> <alpine.DEB.2.20.1609201609130.6905@nanos> <CAHv-k__757zY9DAihbFga4bGYnYchw7pTnOc_uKhbd9UB6GYdA@mail.gmail.com> <alpine.DEB.2.20.1609211720520.5573@nanos> <CAHv-k_-yVqZXJeHugoYg0_XmT0Gb14wv0c+DS1qf5PKUhSMcJA@mail.gmail.com>
X-Original-Sender	linux-kernel-owner@vger.kernel.org
Xref	csiph.com linux.kernel:1489143

Show key headers only | View raw

Binoy,

On Thu, 22 Sep 2016, Binoy Jayan wrote:
> The condition 'ktime_to_ns(tim) < ktime_to_ns(now)' checks if the timer
> has already expired w.r.t. 'soft timeout' value as it does not include
> the slack value 'delta_ns'. In that case 'tim_expiry' is normalized to
> the current time.

You are halfways coming close to the point why this is done, but your
conclusion is completely wrong.  The correct keyword is "expired", but
anything else is just random speculation.

> (I was under the impression that this inaccuracy
> could be because timer was initially running on a different cpu. If that
> is not the case, I guess we can use the code mentioned below).

We are not playing a guessing game here.

> I am using 'hrtimer_get_softexpires_tv64' instead of 'hrtimer_get_expires'
> so that 'latency' is never negative. Please let me know if this looks ok.

No it does not. And it won't look correct until you finally sit down and
decode and understand the functionality behind this code.

I'm not going to continue this, as it's not my job to explain you the code
which you are trying to submit.

I'm not blaming you, but I blame the responsible persons inside your
company who task you with that and expect that I'm going to do their work
of explaining to you how that code works.

@Arnd, @Mark: I'm starting to get seriously grumpy about that.

Thanks,

	tglx

Thread

[RFC PATCH v7 0/5] *** Latency histograms *** Binoy Jayan <binoy.jayan@linaro.org> - 2016-09-20 16:00 +0200
  [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset latency Binoy Jayan <binoy.jayan@linaro.org> - 2016-09-20 16:00 +0200
    Re: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset  latency Thomas Gleixner <tglx@linutronix.de> - 2016-09-20 16:30 +0200
      Re: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset latency Binoy Jayan <binoy.jayan@linaro.org> - 2016-09-21 08:10 +0200
        Re: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset  latency Thomas Gleixner <tglx@linutronix.de> - 2016-09-21 18:10 +0200
          Re: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset latency Binoy Jayan <binoy.jayan@linaro.org> - 2016-09-22 11:20 +0200
            Re: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset  latency Thomas Gleixner <tglx@linutronix.de> - 2016-09-22 19:40 +0200
              Re: [RFC PATCH v7 4/5] tracing: Measure delayed hrtimer offset  latency Mark Brown <broonie@kernel.org> - 2016-09-22 21:30 +0200
  [RFC PATCH v7 2/5] tracing: Add hist trigger support for generic fields Binoy Jayan <binoy.jayan@linaro.org> - 2016-09-20 16:00 +0200
  [RFC PATCH v7 5/5] tracing: wakeup latency events and histograms Binoy Jayan <binoy.jayan@linaro.org> - 2016-09-20 16:00 +0200
  [RFC PATCH v7 3/5] tracing: Add preemptirqsoff timing events Binoy Jayan <binoy.jayan@linaro.org> - 2016-09-20 16:00 +0200
  [RFC PATCH v7 1/5] tracing: Dereference pointers without RCU checks Binoy Jayan <binoy.jayan@linaro.org> - 2016-09-20 16:00 +0200

csiph-web