linux-kernel - Re: [PATCH v4 3/4] sched/fair: Rework sched_use_asym_prio() and sched_asym

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Date: Fri, 9 Feb 2024 19:08:52 +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>,
 Daniel Bristot de Oliveira <bristot@...hat.com>,
 Valentin Schneider <vschneid@...hat.com>, linux-kernel@...r.kernel.org,
 yangyicong@...ilicon.com
Subject: Re: [PATCH v4 3/4] sched/fair: Rework sched_use_asym_prio() and
 sched_asym_prefer()



On 2/9/24 10:47 AM, Ricardo Neri wrote:
> On Wed, Feb 07, 2024 at 11:47:03AM +0800, alexs@...nel.org wrote:
>> From: Alex Shi <alexs@...nel.org>
>>
>> sched_use_asym_prio() sched_asym_prefer() are used together in various
> 
> s/prio() sched/prio() and sched/

Will take it, Thanks!

> 
>> places. Consolidate them into a single function sched_asym().
>>
>> The existing sched_group_asym() is only used when collecting statistics
>> of a scheduling group. Rename it as sched_group_asym().
>> This makes the code easier to read. No functional changes.
>>
>> Signed-off-by: Alex Shi <alexs@...nel.org>
>> To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
>> 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 | 37 ++++++++++++++++++++-----------------
>>  1 file changed, 20 insertions(+), 17 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 607dc310b355..942b6358f683 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -9746,8 +9746,18 @@ static bool sched_use_asym_prio(struct sched_domain *sd, int cpu)
>>  	return sd->flags & SD_SHARE_CPUCAPACITY || is_core_idle(cpu);
>>  }
>>  
>> +static inline bool sched_asym(struct sched_domain *sd, int dst_cpu, int src_cpu)
>> +{
>> +	/*
>> +	 * First check if @dst_cpu can do asym_packing load balance. Only do it
>> +	 * if it has higher priority than @src_cpu.
>> +	 */
>> +	return sched_use_asym_prio(sd, dst_cpu) &&
>> +		sched_asym_prefer(dst_cpu, src_cpu);
>> +}
>> +
>>  /**
>> - * sched_asym - Check if the destination CPU can do asym_packing load balance
>> + * sched_group_asym - Check if the destination CPU can do asym_packing balance
>>   * @env:	The load balancing environment
>>   * @sgs:	Load-balancing statistics of the candidate busiest group
>>   * @group:	The candidate busiest group
> 
> After renaming and changing this function now its documentation has become
> obsolete. Can you update it?

Since the function sched_use_asym_prio() and sched_asym_prefer() both give detailed comments for their actions, as long as this function does, could we just remove the bit obsolete comments here?


@@ -9765,14 +9765,6 @@ static inline bool sched_asym(struct sched_domain *sd, int dst_cpu, int src_cpu)
  * @env::dst_cpu can do asym_packing if it has higher priority than the
  * preferred CPU of @group.
  *
- * SMT is a special case. If we are balancing load between cores, @env::dst_cpu
- * can do asym_packing balance only if all its SMT siblings are idle. Also, it
- * can only do it if @group is an SMT group and has exactly on busy CPU. Larger
- * imbalances in the number of CPUS are dealt with in find_busiest_group().
- *
- * If we are balancing load within an SMT core, or at PKG domain level, always
- * proceed.
- *
  * Return: true if @env::dst_cpu can do with asym_packing load balance. False
  * otherwise.
>