linux-kernel - Re: [PATCH v2] sched_ext: switch class when preempted by higher priority scheduler

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Message-ID: <1164966b-edae-470a-b36b-b08d952d897b@126.com>
Date: Wed, 8 Jan 2025 19:00:43 +0800
From: Honglei Wang <jameshongleiwang@....com>
To: Andrea Righi <arighi@...dia.com>
Cc: tj@...nel.org, void@...ifault.com, changwoo@...lia.com, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, vincent.guittot@...aro.org,
 dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
 mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched_ext: switch class when preempted by higher
 priority scheduler



On 2025/1/8 17:05, Andrea Righi wrote:
> Hi Honglei,
> 
> On Wed, Jan 08, 2025 at 10:33:28AM +0800, Honglei Wang wrote:
>> ops.cpu_release() function, if defined, must be invoked when preempted by
>> a higher priority scheduler class task. This scenario was skipped in
>> commit f422316d7466 ("sched_ext: Remove switch_class_scx()"). Let's fix
>> it.
>>
>> Fixes: f422316d7466 ("sched_ext: Remove switch_class_scx()")
>> Signed-off-by: Honglei Wang <jameshongleiwang@....com>
> 
> Thanks a lot for catching this, I've also reproduced a stall (due to the
> missing ops.cpu_release() invocation) and verified that your fixes resolve
> the problem, so:
> 
> Acked-by: Andrea Righi <arighi@...dia.com>
> 

Thanks a lot for looking at the code and the test, Andrea.

>> ---
>>  kernel/sched/ext.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
>> index 19d2699cf638..ef0e3f2c1e6f 100644
>> --- a/kernel/sched/ext.c
>> +++ b/kernel/sched/ext.c
>> @@ -3034,7 +3034,7 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p,
>>  		 */
>>  		if (p->scx.slice && !scx_rq_bypassing(rq)) {
>>  			dispatch_enqueue(&rq->scx.local_dsq, p, SCX_ENQ_HEAD);
>> -			return;
>> +			goto switch_class;
>>  		}
>>  
>>  		/*
>> @@ -3051,6 +3051,7 @@ static void put_prev_task_scx(struct rq *rq, struct task_struct *p,
>>  		}
>>  	}
>>  
>> +switch_class:
>>  	if (next && next->sched_class != &ext_sched_class)
>>  		switch_class(rq, next);
>>  }
>> -- 
>> 2.45.2
>>
> 
> -Andrea