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SubjectRe: [PATCH v3 4/5] sched/pelt: Add a new runnable average signal
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On 20/02/2020 14:36, Vincent Guittot wrote:
> I agree that setting by default to SCHED_CAPACITY_SCALE is too much
> for little core.
> The problem for little core can be fixed by using the cpu capacity instead
>

So that's indeed better for big.LITTLE & co. Any reason however for not
aligning with the initialization of util_avg ?

With the default MC imbalance_pct (117), it takes 875 utilization to make
a single CPU group (with 1024 capacity) overloaded (group_is_overloaded()).
For a completely idle CPU, that means forking at least 3 tasks (512 + 256 +
128 util_avg)

With your change, it only takes 2 tasks. I know I'm being nitpicky here, but
I feel like those should be aligned, unless we have a proper argument against
it - in which case this should also appear in the changelog with so far only
mentions issues with util_avg migration, not the fork time initialization.

> @@ -796,6 +794,8 @@ void post_init_entity_util_avg(struct task_struct *p)
> }
> }
>
> + sa->runnable_avg = cpu_scale;
> +
> if (p->sched_class != &fair_sched_class) {
> /*
> * For !fair tasks do:
>>
>>> sa->load_avg = scale_load_down(se->load.weight);
>>> + }
>>>
>>> /* when this task enqueue'ed, it will contribute to its cfs_rq's load_avg */
>>> }

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