linux-kernel - Re: [PATCH 2/2] sched/fair: Use rq in idle_cpu

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Message-ID: <647e6f54-8247-4ee6-b2ed-2b49bfdece06@arm.com>
Date: Thu, 4 Jan 2024 17:12:22 +0100
From: Pierre Gondois <pierre.gondois@....com>
To: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
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 2/2] sched/fair: Use rq in idle_cpu_without()

Hello Shrikanth,

On 1/4/24 06:15, Shrikanth Hegde wrote:
> 
> 
> On 1/3/24 6:26 PM, Pierre Gondois wrote:
>> idle_cpu_without() could receive a 'struct rq' instead of a
>> cpu number to avoid converting the cpu number to a 'struct rq'
> 
> nit: s/cpu/CPU
> 
>> two times. Indeed update_sg_wakeup_stats() already makes the
>> conversion.
> 
> This change looks good. There maybe other candidates which might get simplified
> as well. for example, update_blocked_averages. (and then there are some
> like balance_push_set which maybe borderline when it comes to such simplification)

Ok yes, I'll check the functions you pointed out.

> 
>>
>> Signed-off-by: Pierre Gondois <pierre.gondois@....com>
>> ---
>>   kernel/sched/fair.c | 8 +++-----
>>   1 file changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 93e928e76959..d38fec26fd3d 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -10184,15 +10184,13 @@ static unsigned int task_running_on_cpu(int cpu, struct task_struct *p)
>>   
>>   /**
>>    * idle_cpu_without - would a given CPU be idle without p ?
>> - * @cpu: the processor on which idleness is tested.
>> + * @rq: the rq on which idleness is tested.
>>    * @p: task which should be ignored.
>>    *
>>    * Return: 1 if the CPU would be idle. 0 otherwise.
>>    */
>> -static int idle_cpu_without(int cpu, struct task_struct *p)
>> +static int idle_cpu_without(struct rq *rq, struct task_struct *p)
> 
> This might need change in the function name too. perception here is that, is the
> CPU idle without task p.

Yes right, I'll rename to idle_rq_without() in the next version.

Regards,
Pierre

> Otherwise LGTM.
> 
> Reviewed-by: Shrikanth Hegde <sshegde@...ux.vnet.ibm.com>
> 
>>   {
>> -	struct rq *rq = cpu_rq(cpu);
>> -
>>   	if (rq->curr != rq->idle && rq->curr != p)
>>   		return 0;
>>   
>> @@ -10247,7 +10245,7 @@ static inline void update_sg_wakeup_stats(struct sched_domain *sd,
>>   		/*
>>   		 * No need to call idle_cpu_without() if nr_running is not 0
>>   		 */
>> -		if (!nr_running && idle_cpu_without(i, p))
>> +		if (!nr_running && idle_cpu_without(rq, p))
>>   			sgs->idle_cpus++;
>>   
>>   		/* Check if task fits in the CPU */
> 
>