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SubjectRe: [PATCH 03/30] thread_info: tif_need_resched() now takes resched_t as param
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Thomas Gleixner <tglx@linutronix.de> writes:

> On Wed, Feb 14 2024 at 14:08, Mark Rutland wrote:
>> On Mon, Feb 12, 2024 at 09:55:27PM -0800, Ankur Arora wrote:
>>>
>>> -static __always_inline bool tif_need_resched(void)
>>> +static __always_inline bool __tif_need_resched(int nr_flag)
>>> {
>>> - return test_bit(TIF_NEED_RESCHED,
>>> - (unsigned long *)(&current_thread_info()->flags));
>>> + return test_bit(nr_flag,
>>> + (unsigned long *)(&current_thread_info()->flags));
>>> }
>>>
>>> #endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */
>>>
>>> +static __always_inline bool tif_need_resched(resched_t rs)
>>> +{
>>> + /*
>>> + * With !PREEMPT_AUTO tif_need_resched(NR_lazy) is defined
>>> + * as TIF_NEED_RESCHED (the TIF_NEED_RESCHED_LAZY flag is not
>>> + * defined). Return false in that case.
>>> + */
>>> + if (IS_ENABLED(CONFIG_PREEMPT_AUTO) || rs == NR_now)
>>> + return __tif_need_resched(tif_resched(rs));
>>> + else
>>> + return false;
>>> +}
>>
>> As above, I think this would be a bit simpler/clearer if we did:
>>
>> static __always_inline bool tif_need_resched_now(void)
>> {
>> return __tif_need_resched(TIF_NEED_RESCHED);
>> }
>>
>> static __always_inline bool tif_need_resched_lazy(void)
>> {
>> return IS_ENABLED(CONFIG_PREEMPT_AUTO) &&
>> __tif_need_resched(TIF_NEED_RESCHED_LAZY);
>> }
>
> Yes please.

As I wrote to Mark in the sibling subthread, I think exposing
the lazy variants outside of the scheduler isn't really needed.

Non-scheduler/non-entry code only cares about checking if it needs
to do reschedule now. So, I think we can get away with just having:

static __always_inline bool __tif_need_resched(resched_t rs)
{
/*
* With !PREEMPT_AUTO tif_need_resched(NR_lazy) is defined
* as TIF_NEED_RESCHED (the TIF_NEED_RESCHED_LAZY flag is not
* defined). Return false in that case.
*/
if (IS_ENABLED(CONFIG_PREEMPT_AUTO) || rs == NR_now)
return tif_need_resched_bitop(tif_resched(rs));
else
return false;
}

static __always_inline bool tif_need_resched(void)
{
return __tif_need_resched(NR_now);
}

(and similar for all the other interfaces.)

This way lazy and eager just becomes an implementation detail which
which seems to also match nicely to the point of PREEMPT_AUTO.

--
ankur

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