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

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Message-ID: <d774a762-5787-46db-ac3c-2c8e8b76a9c9@linux.ibm.com>
Date: Thu, 20 Nov 2025 11:52:03 +0530
From: Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
To: K Prateek Nayak <kprateek.nayak@....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,
        Madadi Vineeth Reddy <vineethr@...ux.ibm.com>
Subject: Re: [PATCH 1/5] sched/psi: Make psi stubs consistent for !CONFIG_PSI

Hi Prateek,

On 20/11/25 11:40, K Prateek Nayak wrote:
> 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/

Thanks for pointing this out. While going through the discussion I had seen it
in John's tree, but I hadn't realized it was already posted upstream.

I gave the Reviewed-by since the first two cleanup patches still seem valid
and can go in independently of that alternate fix.

Thanks,
Vineeth

> 
> 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.
>