Re: [PATCH v9 04/10] sched: Make sched entity usage tracking scale-invariant
From: Morten Rasmussen
Date: Fri Nov 21 2014 - 07:35:10 EST
On Mon, Nov 03, 2014 at 04:54:41PM +0000, Vincent Guittot wrote:
> From: Morten Rasmussen <morten.rasmussen@xxxxxxx>
> Apply frequency scale-invariance correction factor to usage tracking.
> Each segment of the running_load_avg geometric series is now scaled by the
> current frequency so the utilization_avg_contrib of each entity will be
> invariant with frequency scaling. As a result, utilization_load_avg which is
> the sum of utilization_avg_contrib, becomes invariant too. So the usage level
s/sum of utilization_avg_contrib/sum of sched_entity
> that is returned by get_cpu_usage, stays relative to the max frequency as the
> cpu_capacity which is is compared against.
The last bit doesn't parse right. '... Maybe it is better to drop
the reference to get_cpu_usage which hasn't been defined yet and rewrite
the thing to:
Apply frequency scale-invariance correction factor to utilization
tracking. Each segment of the running_load_avg geometric series is now
scaled by the current frequency so the utilization_avg_contrib of each
entity will be invariant with frequency scaling. As a result,
utilization_load_avg which is the sum of sched_entity
utilization_avg_contribs becomes invariant too and is now relative to
the max utilization at the max frequency (=cpu_capacity).
I think we should add:
arch_scale_freq_capacity() is reintroduced to provide the frequency
compensation scaling factor.
> Then, we want the keep the load tracking values in a 32bits type, which implies
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