linux-kernel - Re: [PATCH 1/3] cpuidle: Store the idle start time stamp

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Message-ID: <20150415131157.GO23123@twins.programming.kicks-ass.net>
Date:	Wed, 15 Apr 2015 15:11:57 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:	rjw@...ysocki.net, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, nicolas.pitre@...aro.org
Subject: Re: [PATCH 1/3] cpuidle: Store the idle start time stamp

On Wed, Apr 15, 2015 at 02:50:33PM +0200, Daniel Lezcano wrote:
> I was thinking about converting to nanosecond the cpuidle framework but it
> is not worth to do that as the resolution is too high for the idle states.

The question is if saving those 4 bytes (unsigned int vs u64) on
next_timer_us is worth having to do that /1000 all the time.

The one spot where its used:

        new_factor += RESOLUTION * measured_us / data->next_timer_us;

Could be fixed with a few shifts, all that matters is that measured_us
and next_timer_us are in the same metric, it doesn't need to be us, it
could be ns/1024 for instance.
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