linux-kernel - Re: [PATCH] cpuidle: add 'failed' statistic

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Message-ID: <531F85AC.3000404@linaro.org>
Date:	Tue, 11 Mar 2014 22:52:44 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Len Brown <lenb@...nel.org>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpuidle: add 'failed' statistic

On 03/11/2014 03:00 AM, Len Brown wrote:
> Exactly what use-case do you have in mind for this attribute?

Nothing more than balance the c-state usage with the selection 
efficiency of this state. The current statistics do not give a lot of 
clues of what is happening.

> "failed" is a strong word.
> Some validation guy is going to send me e-mail when it is non-zero...
> I don't like that use-case.
>
> But even if re-named, I don't see see how it will be useful.
> When I want to see how C-state predictions are doing, I use ftrace,
> which can show me the actual expected and actual times, not just a count
> of how man times predicted was < actual.

Mmh, where do you retrieve the target_residency from userspace ? This 
information is not exported from ftrace neither sysfs.

> I would rather see some good tracepoints go upstream.

Ok, which tracepoints you would like to see ?

target residency=%lu, expected residency=%lu, measured residency=%lu

??

Thanks
   -- Daniel


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