linux-kernel - Re: [RFC PATCH v5 09/10] thermal: add trace events to the power allocator governor

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Date:	Fri, 11 Jul 2014 09:27:55 +0100
From:	"Javi Merino" <javi.merino@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Punit Agrawal <Punit.Agrawal@....com>,
	"broonie@...nel.org" <broonie@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Eduardo Valentin <edubezval@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [RFC PATCH v5 09/10] thermal: add trace events to the power
 allocator governor

On Thu, Jul 10, 2014 at 07:03:50PM +0100, Steven Rostedt wrote:
> On Thu, 10 Jul 2014 17:20:14 +0100
> "Javi Merino" <javi.merino@....com> wrote:
> 
> 
> > > 
> > > How many CPUs are you saving load_cpu on? A trace event can't be bigger
> > > than a page. And the data is actually a little less than that with the
> > > required headers.
> > 
> > The biggest system I've tested it on is an 8 cpu system (with
> > NR_CPUS==8).  So yes, small and we haven't seen any issues.
> > 
> > Are you saying that we are siphoning too much data through ftrace?  He
> > find it really valuable to collect information during run and process
> > it afterwards but I can see how this may not be feasible for systems
> > with thousands of cpus.
> 
> Only too much for a single event. Perhaps have the tracepoint post per
> CPU? Then you wouldn't need that array.

Sounds good, I'll do that.

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