linux-kernel - Re: [PATCH 1/5] sched/psi: Make psi stubs consistent for !CONFIG

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Message-ID: <892917ec-15b3-4852-b12f-9232e438802f@amd.com>
Date: Thu, 20 Nov 2025 11:40:11 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Madadi Vineeth Reddy <vineethr@...ux.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>, John Stultz <jstultz@...gle.com>, Johannes
 Weiner <hannes@...xchg.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>, Suren
 Baghdasaryan <surenb@...gle.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/5] sched/psi: Make psi stubs consistent for !CONFIG_PSI

Hello Vineeth,

On 11/20/2025 11:29 AM, Madadi Vineeth Reddy wrote:
> On 18/11/25 00:25, K Prateek Nayak wrote:
>> commit 1a6151017ee5 ("sched: psi: pass enqueue/dequeue flags to psi
>> callbacks directly") modified the psi_enqueue() and psi_dequeue()
>> functions to take the complete enqueue/dequeue flags but left the stubs
>> for !CONFIG_PSI unaltered.
>>
>> Modify the stubs to also accept the flags argument to keep it consistent
>> with CONFIG_PSI.
>>
>> Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
>> ---
>>  kernel/sched/stats.h | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
>> index cbf7206b3f9d..3323d773fec3 100644
>> --- a/kernel/sched/stats.h
>> +++ b/kernel/sched/stats.h
>> @@ -221,8 +221,8 @@ static inline void psi_sched_switch(struct task_struct *prev,
>>  }
>>  
>>  #else /* !CONFIG_PSI: */
>> -static inline void psi_enqueue(struct task_struct *p, bool migrate) {}
>> -static inline void psi_dequeue(struct task_struct *p, bool migrate) {}
>> +static inline void psi_enqueue(struct task_struct *p, int flags) {}
>> +static inline void psi_dequeue(struct task_struct *p, int flags) {}
>>  static inline void psi_ttwu_dequeue(struct task_struct *p) {}
>>  static inline void psi_sched_switch(struct task_struct *prev,
>>  				    struct task_struct *next,
> 
> Right. The commit that updated the function signature did not update the
> !CONFIG_PSI stubs accordingly. This patch corrects that.
> 
> Reviewed-by: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>

Thanks for the review.

P.S. John has an alternate fix for the same at
https://lore.kernel.org/lkml/20251118055242.4030849-1-jstultz@google.com/

That considers a blocked donor as a runnable entity from PSI
standpoint.

This series implements the alternate approach of blocking the PSI signals
when the blocked donor is retained on the rq, skipping the block_task()
and it enqueues the PSI signal back when the donor is woken up again.

-- 
Thanks and Regards,
Prateek