linux-kernel - Re: [PATCH 05/30] sched: *_tsk_need_resched() now takes resched

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Date: Tue, 20 Feb 2024 14:37:01 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
        torvalds@...ux-foundation.org, paulmck@...nel.org,
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        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        Ankur Arora
 <ankur.a.arora@...cle.com>
Subject: Re: [PATCH 05/30] sched: *_tsk_need_resched() now takes resched_t
 as param


Thomas Gleixner <tglx@...utronix.de> writes:

> On Mon, Feb 12 2024 at 21:55, Ankur Arora wrote:
>
> The subject line reads odd...
>
>> -static inline bool test_tsk_need_resched(struct task_struct *tsk)
>> +static inline bool test_tsk_need_resched(struct task_struct *tsk, resched_t rs)
>>  {
>> -	return unlikely(test_tsk_thread_flag(tsk,TIF_NEED_RESCHED));
>> +	if (IS_ENABLED(CONFIG_PREEMPT_AUTO) || rs == NR_now)
>> +		return unlikely(test_tsk_thread_flag(tsk, tif_resched(rs)));
>> +	else
>> +		return false;
>>  }
>
> Same like the others. This wants wrappers with now/lazy.

So, when working on the scheduler changes, I found the simplest
implementation was to define a function that takes into account
current preemption mode, checks for idle, tick etc and returns
the rescheduling policy, which __resched_curr() carries out.

So, it would be useful to just pass the resched_t as a parameter
instead of having now/lazy wrappers.

That said, as I mention in the other thread, the current primitives
are unnecessarily noisy because everyone needs to use it.

   -static inline bool test_tsk_need_resched(struct task_struct *tsk, resched_t rs)
   +static inline bool __test_tsk_need_resched(struct task_struct *tsk, resched_t rs)
   {
           if (IS_ENABLED(CONFIG_PREEMPT_AUTO) || rs == NR_now)
                   return unlikely(test_tsk_thread_flag(tsk, tif_resched(rs)));
   @@ -1980,6 +1985,11 @@ static inline bool test_tsk_need_resched(struct task_struct *tsk, resched_t rs)
                   return false;
   }

   +static inline bool test_tsk_need_resched(struct task_struct *tsk)
   +{
   +	return __test_tsk_need_resched(tsk, NR_now);
   +}
   +

How about something like this (and similar elsewhere)?

>>  /*
>> @@ -2104,7 +2121,8 @@ static __always_inline bool need_resched(void)
>>
>>  static __always_inline bool need_resched_lazy(void)
>>  {
>> -	return unlikely(tif_need_resched(NR_lazy));
>> +	return IS_ENABLED(CONFIG_PREEMPT_AUTO) &&
>> +		unlikely(tif_need_resched(NR_lazy));
>
> Shouldn't this be folded into the patch which adds need_resched_lazy()?

I think I had messed up a rebase. Will fix.

Thanks

--
ankur