linux-kernel - Re: [PATCH] arm: add cpu_idle tracepoints to arch_cpu

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Message-ID: <20150916130053.7a1a7f62@gandalf.local.home>
Date:	Wed, 16 Sep 2015 13:00:53 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Jisheng Zhang <jszhang@...vell.com>,
	Ingo Molnar <mingo@...hat.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Thomas Renninger <trenn@...e.de>
Subject: Re: [PATCH] arm: add cpu_idle tracepoints to arch_cpu_idle

On Wed, 16 Sep 2015 12:41:28 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> [ Added Arjan, as he knows powertop better, as well as
>  Thomas Renninger, that added the cpu_idle trace event ]
> 
> On Wed, 16 Sep 2015 17:28:18 +0100
> Russell King - ARM Linux <linux@....linux.org.uk> wrote:
> 
> > On Wed, Sep 16, 2015 at 10:37:00PM +0800, Jisheng Zhang wrote:
> > > Currently, if cpuidle is disabled or not supported, powertop reports
> > > zero wakeups and zero events. This is due to the cpu_idle tracepoints
> > > are missing.
> > > 
> > > This patch is to make cpu_idle tracepoints always available even if
> > > cpuidle is disabled or not supported.
> > 
> > This seems like a hack to me.  These are cpu_idle tracepoints which
> > tell people when something happens in cpuidle.  If cpuidle is disabled,
> > then surely the tracepoints shouldn't fire.
> > 
> > However, I'll leave it to the tracing people to have the final word on
> > whether this is the right thing to do as I've very little experience
> > with the tracing design.
> 
> Adding back the change log for the original patch:

Bah, it was in the original email. I accidentally double clicked on the
reply part, and claws-mail collapsed it. I never read the change log
via this email because of that.

Sorry Russell, my mistake :-/

-- Steve


> 
> "Currently, if cpuidle is disabled or not supported, powertop reports
> zero wakeups and zero events. This is due to the cpu_idle tracepoints
> are missing.
> 
> This patch is to make cpu_idle tracepoints always available even if
> cpuidle is disabled or not supported."
> 
> This is the same code that sits in x86. I'm assuming it is fine. But
> I'm not an expert on the cpu_idle trace event.
--
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