linux-kernel - Re: [PATCH] sched/fair: Remove stale references to LAST_BUDDY and SKIP

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Message-ID: <13be1ce2-85b5-46e2-aab8-94aa7f8a0cfe@linux.ibm.com>
Date: Thu, 7 Aug 2025 12:07:27 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: 20250314090128.25141-1-vineethr@...ux.ibm.com,
        Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>
Cc: 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>, Valentin Schneider <vschneid@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Adam Li
 <adamli@...amperecomputing.com>,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: Re: [PATCH] sched/fair: Remove stale references to LAST_BUDDY and
 SKIP_BUDDY

On 13/04/25 09:40, Madadi Vineeth Reddy wrote:
> Hi Peter, Ingo,
> 
> Ping.
> 
> Any thoughts on this? Can it be picked up?
> 
> Thanks,
> Madadi Vineeth Reddy

Hi Peter, Ingo,

This still applies cleanly on top of tip/sched/core.

Could this be considered for merging?

Thank you,
Madadi Vineeth Reddy

> 
> On 14/03/25 14:31, Madadi Vineeth Reddy wrote:
>> Commit 5e963f2bd465 ("sched/fair: Commit to EEVDF") removed the
>> functionality associated with LAST_BUDDY and SKIP_BUDDY. However,
>> some outdated references remained in the comments for pick_next_entity
>> and check_preempt_wakeup_fair. This commit cleans up those comments
>> to maintain clarity and correctness.
>>
>> No functional change intended.
>>
>> Co-developed-by: Adam Li <adamli@...amperecomputing.com>
>> Signed-off-by: Adam Li <adamli@...amperecomputing.com>
>> Signed-off-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
>> ---
>>  kernel/sched/fair.c | 6 +-----
>>  1 file changed, 1 insertion(+), 5 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 9dafb374d76d..379dbcbb24e9 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5578,8 +5578,6 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags);
>>   * Pick the next process, keeping these things in mind, in this order:
>>   * 1) keep things fair between processes/task groups
>>   * 2) pick the "next" process, since someone really wants that to run
>> - * 3) pick the "last" process, for cache locality
>> - * 4) do not run the "skip" process, if something else is available
>>   */
>>  static struct sched_entity *
>>  pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
>> @@ -8780,9 +8778,7 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
>>  	 *
>>  	 * Note: this also catches the edge-case of curr being in a throttled
>>  	 * group (e.g. via set_curr_task), since update_curr() (in the
>> -	 * enqueue of curr) will have resulted in resched being set.  This
>> -	 * prevents us from potentially nominating it as a false LAST_BUDDY
>> -	 * below.
>> +	 * enqueue of curr) will have resulted in resched being set.
>>  	 */
>>  	if (test_tsk_need_resched(rq->curr))
>>  		return;
>