Re: [PATCH 04/10] sched/fair: Dynamically update cfs_overload_cpus

[Steven Sistare]

On 10/22/2018 12:56 PM, Peter Zijlstra wrote:
> On Mon, Oct 22, 2018 at 07:59:35AM -0700, Steve Sistare wrote:
>> An overloaded CPU has more than 1 runnable task.  When a CFS task wakes
>> on a CPU, if h_nr_running transitions from 1 to more, then set the CPU in
>> the cfs_overload_cpus bitmap.  When a CFS task sleeps, if h_nr_running
>> transitions from 2 to less, then clear the CPU in cfs_overload_cpus.
> 
>> @@ -5111,8 +5147,12 @@ static inline void hrtick_update(struct rq *rq)
>>  		update_cfs_group(se);
>>  	}
>>  
>> -	if (!se)
>> +	if (!se) {
>>  		add_nr_running(rq, 1);
>> +		if (prev_nr == 1)
>> +			overload_set(rq);
>> +
>> +	}
> 
> This is very similar to what RT already has, except they also track if
> the tasks in question is in fact migratable (p->nr_cpus_allowed > 1).
> 
> And similarly, it might make sense to use the sparse mask thing over
> there.

Yes.  I forgot to mention RT as likely follow on work.

- Steve