Quoting Morten Rasmussen (2015-07-07 11:24:27)
> From: Juri Lelli <juri.le...@arm.com>
>
> Since the true utilization of a long running task is not detectable while
> it is running and might be bigger than the current cpu capacity, create the
> maximum cpu capacity head room by requesting the maximum cpu capacity once
> the cpu usage plus the capacity margin exceeds the current capacity. This
> is also done to try to harm the performance of a task the least.
>
> cc: Ingo Molnar <mi...@redhat.com>
> cc: Peter Zijlstra <pet...@infradead.org>
>
> Signed-off-by: Juri Lelli <juri.le...@arm.com>
> ---
> kernel/sched/fair.c | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 323331f..c2d6de4 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -8586,6 +8586,25 @@ static void task_tick_fair(struct rq *rq, struct
> task_struct *curr, int queued)
>
> if (!rq->rd->overutilized && cpu_overutilized(task_cpu(curr)))
> rq->rd->overutilized = true;
> +
> + /*
> + * To make free room for a task that is building up its "real"
> + * utilization and to harm its performance the least, request a
> + * jump to max OPP as soon as get_cpu_usage() crosses the UP
> + * threshold. The UP threshold is built relative to the current
> + * capacity (OPP), by using same margin used to tell if a cpu
> + * is overutilized (capacity_margin).
> + */
> + if (sched_energy_freq()) {
> + int cpu = cpu_of(rq);
> + unsigned long capacity_orig = capacity_orig_of(cpu);
> + unsigned long capacity_curr = capacity_curr_of(cpu);
> +
> + if (capacity_curr < capacity_orig &&
> + (capacity_curr * SCHED_LOAD_SCALE) <
> + (get_cpu_usage(cpu) * capacity_margin))
> + cpufreq_sched_set_cap(cpu, capacity_orig);
I'm sure that at some point the Product People are going to want to tune
the capacity value that is requested. Hard-coding the max
capacity/frequency in is a reasonable start, but at some point it would
be nice to fetch an intermediate capacity defined by the cpufreq driver
for this particular cpu. We have already seen that a lot in Android
devices using the interactive governor and it could be done from
cpufreq_sched_start().
Regards,
Mike
> + }
> }
>
> /*
> --
> 1.9.1
>
> --
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