Re: [PATCH v2] sched/freq: move call to cpufreq_update_util

[Valentin Schneider <valentin.schneider@arm.com>]

Hi Vincent,

I didn't see anything in that reply, was that just a spurious email?

On 12/11/2019 15:05, Vincent Guittot wrote:
> Le Tuesday 12 Nov 2019 à 15:48:13 (+0100), Vincent Guittot a écrit :
>> update_cfs_rq_load_avg() calls cfs_rq_util_change() everytime pelt decays,
>> which might be inefficient when cpufreq driver has rate limitation.
>>
>> When a task is attached on a CPU, we have call path:
>>
>> update_blocked_averages()
>>   update_cfs_rq_load_avg()
>>     cfs_rq_util_change -- > trig frequency update
>>   attach_entity_load_avg()
>>     cfs_rq_util_change -- > trig frequency update
>>
>> The 1st frequency update will not take into account the utilization of the
>> newly attached task and the 2nd one might be discard because of rate
>> limitation of the cpufreq driver.
>>
>> update_cfs_rq_load_avg() is only called by update_blocked_averages()
>> and update_load_avg() so we can move the call to
>> {cfs_rq,cpufreq}_util_change() into these 2 functions. It's also
>> interesting to notice that update_load_avg() already calls directly
>> cfs_rq_util_change() for !SMP case.
>>
>> This changes will also ensure that cpufreq_update_util() is called even
>> when there is no more CFS rq in the leaf_cfs_rq_list to update but only
>> irq, rt or dl pelt signals.
>>
>> Reported-by: Doug Smythies <dsmythies@telus.net>
>> Fixes: 039ae8bcf7a5 ("sched/fair: Fix O(nr_cgroups) in the load balancing path")
>> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
>>
>> ---
>>
>> I have just rebased the patch on latest tip/sched/core and made it a proper
>> patchset after Doug reported that the problem has diseappeared according to
>> his 1st results but tests results are not all based on the same v5.4-rcX
>> and with menu instead of teo governor.
>>
>>  kernel/sched/fair.c | 33 +++++++++++++++++++++------------
>>  1 file changed, 21 insertions(+), 12 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index e458f52..c93d534 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -3508,9 +3508,6 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)
>>  	cfs_rq->load_last_update_time_copy = sa->last_update_time;
>>  #endif
>>  
>> -	if (decayed)
>> -		cfs_rq_util_change(cfs_rq, 0);
>> -
>>  	return decayed;
>>  }
>>  
>> @@ -3620,8 +3617,12 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
>>  		attach_entity_load_avg(cfs_rq, se, SCHED_CPUFREQ_MIGRATION);
>>  		update_tg_load_avg(cfs_rq, 0);
>>  
>> -	} else if (decayed && (flags & UPDATE_TG))
>> -		update_tg_load_avg(cfs_rq, 0);
>> +	} else if (decayed) {
>> +		cfs_rq_util_change(cfs_rq, 0);
>> +
>> +		if (flags & UPDATE_TG)
>> +			update_tg_load_avg(cfs_rq, 0);
>> +	}
>>  }
>>  
>>  #ifndef CONFIG_64BIT
>> @@ -7484,6 +7485,7 @@ static void update_blocked_averages(int cpu)
>>  	const struct sched_class *curr_class;
>>  	struct rq_flags rf;
>>  	bool done = true;
>> +	int decayed = 0;
>>  
>>  	rq_lock_irqsave(rq, &rf);
>>  	update_rq_clock(rq);
>> @@ -7493,9 +7495,9 @@ static void update_blocked_averages(int cpu)
>>  	 * that RT, DL and IRQ signals have been updated before updating CFS.
>>  	 */
>>  	curr_class = rq->curr->sched_class;
>> -	update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
>> -	update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
>> -	update_irq_load_avg(rq, 0);
>> +	decayed |= update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
>> +	decayed |= update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
>> +	decayed |= update_irq_load_avg(rq, 0);
>>  
>>  	/* Don't need periodic decay once load/util_avg are null */
>>  	if (others_have_blocked(rq))
>> @@ -7529,6 +7531,9 @@ static void update_blocked_averages(int cpu)
>>  	}
>>  
>>  	update_blocked_load_status(rq, !done);
>> +
>> +	if (decayed)
>> +		cpufreq_update_util(rq, 0);
>>  	rq_unlock_irqrestore(rq, &rf);
>>  }
>>  
>> @@ -7585,6 +7590,7 @@ static inline void update_blocked_averages(int cpu)
>>  	struct cfs_rq *cfs_rq = &rq->cfs;
>>  	const struct sched_class *curr_class;
>>  	struct rq_flags rf;
>> +	int decayed = 0;
>>  
>>  	rq_lock_irqsave(rq, &rf);
>>  	update_rq_clock(rq);
>> @@ -7594,13 +7600,16 @@ static inline void update_blocked_averages(int cpu)
>>  	 * that RT, DL and IRQ signals have been updated before updating CFS.
>>  	 */
>>  	curr_class = rq->curr->sched_class;
>> -	update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
>> -	update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
>> -	update_irq_load_avg(rq, 0);
>> +	decayed |= update_rt_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &rt_sched_class);
>> +	decayed |= update_dl_rq_load_avg(rq_clock_pelt(rq), rq, curr_class == &dl_sched_class);
>> +	decayed |= update_irq_load_avg(rq, 0);
>>  
>> -	update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq);
>> +	decayed |= update_cfs_rq_load_avg(cfs_rq_clock_pelt(cfs_rq), cfs_rq);
>>  
>>  	update_blocked_load_status(rq, cfs_rq_has_blocked(cfs_rq) || others_have_blocked(rq));
>> +
>> +	if (decayed)
>> +		cpufreq_update_util(rq, 0);
>>  	rq_unlock_irqrestore(rq, &rf);
>>  }
>>  
>> -- 
>> 2.7.4
>>