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

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Date: Tue, 30 Jan 2024 21:18:30 +0800
From: kuiliang Shi <seakeel@...il.com>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: Shrikanth Hegde <sshegde@...ux.ibm.com>, alexs@...nel.org,
 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 1/26/24 8:06 AM, Ricardo Neri wrote:
> On Thu, Jan 25, 2024 at 05:35:32PM +0800, kuiliang Shi wrote:
>>
>>
>> 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. :(
> 
> This would not work with !SMT and asym_packing.
> 
> I can test your patches on asym_packing + SMT systems if you post a new
> version.
> 

Hi Neri,

Thanks a lot for generous offer! I don't know if my understanding right, but I try my best to have a best guessing in V2 patch for you. :)

Many thanks for the help!

Best regards
Alex