Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED

Thomas Gleixner
2023-09-24T07:55:58Z

On Sun, Sep 24 2023 at 08:19, Matthew Wilcox wrote:
> On Sun, Sep 24, 2023 at 12:50:43AM +0200, Thomas Gleixner wrote:
>> cond_resched() cannot nest and is obviously scope-less.
>>
>> The TIF_ALLOW_RESCHED mechanism, which sparked this discussion only
>> pretends to be scoped.
>>
>> As Peter pointed out it does not properly nest with other mechanisms and
>> it cannot even nest in itself because it is boolean.
>
> We can nest a single bit without turning it into a counter -- we
> do this for memalloc_nofs_save() for example. Simply return the
> current value of the bit, and pass it to _restore().

Right.

That works, but the reverse logic still does not make sense:

allow_resched();
....
spin_lock();

while
resched_now_is_suboptimal();
...
spin_lock();

works.

Thanks,

tglx