Re: [PATCH v2 07/35] sched: define *_tsk_need_resched_lazy() helpers

Peter Zijlstra
2024-05-29T08:25:42Z

On Mon, May 27, 2024 at 05:34:53PM -0700, Ankur Arora wrote:

> static inline void clear_tsk_need_resched(struct task_struct *tsk)
> {
> - clear_tsk_thread_flag(tsk,TIF_NEED_RESCHED);
> + clear_tsk_thread_flag(tsk, tif_resched(RESCHED_NOW));
> +
> + if (IS_ENABLED(CONFIG_PREEMPT_AUTO))
> + clear_tsk_thread_flag(tsk, tif_resched(RESCHED_LAZY));
> +}

(using tif_resched() here is really uncalled for)

So this will generate rather sub-optimal code, namely 2 atomics that
really should be one.

Ideally we'd write this something like:

unsigned long mask = _TIF_NEED_RESCHED;
if (IS_ENABLED(CONFIG_PREEMPT_AUTO))
mask |= _TIF_NEED_RESCHED_LAZY;

atomic_long_andnot(mask, (atomic_long_t *)task_thread_info(tsk)->flags);

Which will clear both bits with a single atomic.