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SubjectRe: [RFC PATCH v3 06/10] sched: Add over-utilization/tipping point indicator
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On 06/19/2018 09:01 AM, Pavan Kondeti wrote:
> On Mon, May 21, 2018 at 03:25:01PM +0100, Quentin Perret wrote:

[...]

>> @@ -8152,6 +8176,9 @@ static inline void update_sg_lb_stats(struct lb_env *env,
>> if (nr_running > 1)
>> *overload = true;
>>
>> + if (cpu_overutilized(i))
>> + *overutilized = 1;
>> +
>
> There is no need to check if every CPU is overutilized or not once
> *overutilized is marked as true, right?

True, so you want to check *overutilized before calling
cpu_overutilized() to save a little bit on compute?

[...]

>> @@ -8586,6 +8621,10 @@ static struct sched_group *find_busiest_group(struct lb_env *env)
>> * this level.
>> */
>> update_sd_lb_stats(env, &sds);
>> +
>> + if (sched_energy_enabled() && !READ_ONCE(env->dst_rq->rd->overutilized))
>> + goto out_balanced;
>> +
>
> Is there any reason for sending no-hz idle kicks but bailing out here when
> system is not overutilized?

Even if a system is not-overutilized, we want to update stale cpu
blocked load and utilization so NOHZ_STATS_KICK have to get through.

So calling find_busiest_group() -> update_sd_lb_stats() ->
update_sg_lb_stats() to possibly execute update_nohz_stats() is IMHO the
right thing to do.

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