Re: [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks

Patrick Bellasi
2018-08-09T15:41:56Z

On 07-Aug 14:54, Quentin Perret wrote:
> Hi Patrick,

Hi Quentin!

> On Monday 06 Aug 2018 at 17:39:38 (+0100), Patrick Bellasi wrote:
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index a7affc729c25..bb25ef66c2d3 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -200,6 +200,7 @@ static unsigned int get_next_freq(struct sugov_policy *sg_policy,
> > static unsigned long sugov_get_util(struct sugov_cpu *sg_cpu)
> > {
> > struct rq *rq = cpu_rq(sg_cpu->cpu);
> > + unsigned long util_cfs, util_rt;
> > unsigned long util, irq, max;
> >
> > sg_cpu->max = max = arch_scale_cpu_capacity(NULL, sg_cpu->cpu);
>
> IIUC, not far below this you should still have something like:
>
> if (rt_rq_is_runnable(&rq->rt))
> return max;

Do you mean that when RT tasks are RUNNABLE we still want to got to
MAX? Not sure to understand... since this patch is actually to clamp
the RT class...

> So you won't reach the actual clamping code at the end of the function
> when a RT task is runnable no?

... mmm... no... this patch is to clamp RT tasks... Am I missing
something?

> Also, I always had the feeling that the default for RT should be
> util_min == 1024, and then users could decide to lower the bar if they
> want to.

Mmm... good point! This would keep the policy unaltered for RT tasks.

I want to keep sched class specific code in uclamp at minimum, but
likely this should be achievable by just properly initializing the
task-specific util_min for RT tasks, if the original task has
UCLAM_NOT_VALID.

> For the specific case of RT, that feels more natural than
> applying a max util clamp IMO. What do you think ?

I'll look better into this for the next posting!

Cheers Patrick

--
#include <best/regards.h>

Patrick Bellasi