linux-kernel - Re: [PATCH 5/5] sched/fair: narrow the sched_use_asym

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Date: Thu, 25 Jan 2024 17:35:32 +0800
From: kuiliang Shi <seakeel@...il.com>
To: Shrikanth Hegde <sshegde@...ux.ibm.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 5/5] sched/fair: narrow the sched_use_asym_prio checking
 scenario



On 1/23/24 4:47 PM, Shrikanth Hegde wrote:
> 
> 
> On 1/17/24 2:27 PM, alexs@...nel.org wrote:
>> From: Alex Shi <alexs@...nel.org>
>>
>> Current function doesn't match it's comments, in fact, core_idle
>> checking is only meaningful with non-SMT.
>> So make the function right.
>>
>> 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 | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 96163ab69ae0..0a321f639c79 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -9741,8 +9741,8 @@ group_type group_classify(unsigned int imbalance_pct,
>>   */
>>  static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
>>  {
>> -	return (!sched_smt_active()) ||
>> -		(sd->flags & SD_SHARE_CPUCAPACITY) || is_core_idle(cpu);
>> +	return	(sd->flags & SD_SHARE_CPUCAPACITY) ||
>> +		(!sched_smt_active() && is_core_idle(cpu));
>>  }
> 
> This seems wrong. This would always return false for higher than SMT domains 
> if smt is active. 
> 

yes, thanks for point out.

> Was this meant to be sched_smt_active() && is_core_idle(cpu)? 

In theory, yes, it should like this. But I have no ASYM device to test. :(

Thanks!
Alex

> 
>>  
>>  static inline bool _sched_asym(struct sched_domain *sd,