linux-kernel - Re: [PATCH 4/5] sched/fair: add a func _sched

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Date: Fri, 26 Jan 2024 09:57:40 +0800
From: kuiliang Shi <seakeel@...il.com>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>, alexs@...nel.org
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira
 <bristot@...hat.com>, Valentin Schneider <vschneid@...hat.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] sched/fair: add a func _sched_asym



On 1/26/24 5:56 AM, Ricardo Neri wrote:
> On Wed, Jan 17, 2024 at 04:57:14PM +0800, alexs@...nel.org wrote:
>> From: Alex Shi <alexs@...nel.org>
>>
>> Use this func in sched_asym and other path to simply code.
>> No function change.
>>
>> Signed-off-by: Alex Shi <alexs@...nel.org>
>> To: Valentin Schneider <vschneid@...hat.com>
>> To: Vincent Guittot <vincent.guittot@...aro.org>
>> To: Peter Zijlstra <peterz@...radead.org>
>> To: Ingo Molnar <mingo@...hat.com>
>> ---
>>  kernel/sched/fair.c | 27 +++++++++++++--------------
>>  1 file changed, 13 insertions(+), 14 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index ebd659af2d78..96163ab69ae0 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -9745,6 +9745,14 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
>>  		(sd->flags & SD_SHARE_CPUCAPACITY) || is_core_idle(cpu);
>>  }
>>  
>> +static inline bool _sched_asym(struct sched_domain *sd,
>> +			int dst_cpu, int repl_cpu)
> 
> What does repl_cpu mean? Maybe renaming to src_cpu?

Uh, src_cpu is better than a 'replacing' cpu. Thanks!

> 
>> +{
>> +	/* Ensure that the whole local core is idle, if applicable. */
>> +	return sched_use_asym_prio(sd, dst_cpu) &&
>> +			sched_asym_prefer(dst_cpu, repl_cpu);
> 
> The comment no longer applies to the whole expression. Perhaps rewording is
> in order. First we check for the whole idle core if applicable (i.e., when
> not balancing among SMT siblings). Then we check priorities.

Right will fix this by v2.
> 
> Also, indentation should be aligned with `return`, IMO.
> 
>> +}
>> +
>>  /**
>>   * sched_asym - Check if the destination CPU can do asym_packing load balance
>>   * @env:	The load balancing environment
>> @@ -9768,20 +9776,13 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
>>  static inline bool
>>  sched_asym(struct lb_env *env, struct sg_lb_stats *sgs, struct sched_group *group)
>>  {
>> -	/* Ensure that the whole local core is idle, if applicable. */
>> -	if (!sched_use_asym_prio(env->sd, env->dst_cpu))
>> -		return false;
>> -
>>  	/*
>>  	 * CPU priorities does not make sense for SMT cores with more than one
>>  	 * busy sibling.
> 
> While here, it might be good to fix a syntax error above: s/does/do/.
> 

Yes, thanks

>>  	 */
>> -	if (group->flags & SD_SHARE_CPUCAPACITY) {
>> -		if (sgs->group_weight - sgs->idle_cpus != 1)
>> -			return false;
>> -	}
>> -
>> -	return sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu);
>> +	return !(group->flags & SD_SHARE_CPUCAPACITY &&
>> +			sgs->group_weight - sgs->idle_cpus != 1) &&
>> +		_sched_asym(env->sd, env->dst_cpu, group->asym_prefer_cpu);
> 
> Perhaps we can come up with a better name than _sched_asym(). After this
> patch the difference between sched_asym() and _sched_asym() is that the
> former considers the stats of the source group. Maybe sched_asym() can be
> renamed as sched_group_asym(); it is only used in update_sg_lb_stats().
> Your _sched_asym() can become sched_asym().

Thanks for good suggestion! will send v2 according your suggestion. 

Alex
> 
>>  }
>>  
>>  /* One group has more than one SMT CPU while the other group does not */
>> @@ -11036,8 +11037,7 @@ static struct rq *find_busiest_queue(struct lb_env *env,
>>  		 * SMT cores with more than one busy sibling.
>>  		 */
>>  		if ((env->sd->flags & SD_ASYM_PACKING) &&
>> -		    sched_use_asym_prio(env->sd, i) &&
>> -		    sched_asym_prefer(i, env->dst_cpu) &&
>> +		    _sched_asym(env->sd, i, env->dst_cpu) &&
>>  		    nr_running == 1)
>>  			continue;
>>  
>> @@ -11907,8 +11907,7 @@ static void nohz_balancer_kick(struct rq *rq)
>>  		 * preferred CPU must be idle.
>>  		 */
>>  		for_each_cpu_and(i, sched_domain_span(sd), nohz.idle_cpus_mask) {
>> -			if (sched_use_asym_prio(sd, i) &&
>> -			    sched_asym_prefer(i, cpu)) {
>> +			if (_sched_asym(sd, i, cpu)) {
>>  				flags = NOHZ_STATS_KICK | NOHZ_BALANCE_KICK;
>>  				goto unlock;
>>  			}
>> -- 
>> 2.43.0
>>