Re: [PATCH v2] sched: set TIF_NEED_RESCHED before calling __trace_set_need_resched()

[Peter Zijlstra]

On Tue, Jun 30, 2026 at 09:46:11PM +0530, K Prateek Nayak wrote:

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 96226707c2f6..934f540d0d3f 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1049,9 +1049,16 @@ static inline void hrtick_schedule_exit(struct rq *rq) { }
>   * this avoids any races wrt polling state changes and thereby avoids
>   * spurious IPIs.
>   */
> -static inline bool set_nr_and_not_polling(struct thread_info *ti, int tif)
> +static inline bool set_nr_and_not_polling(struct rq *rq, int tif)
>  {
> -	return !(fetch_or(&ti->flags, 1 << tif) & _TIF_POLLING_NRFLAG);
> +	struct task_struct *curr = rq->curr;
> +	struct thread_info *ti = task_thread_info(curr);
> +	unsigned long old_flags = fetch_or(&ti->flags, 1 << tif);
> +
> +	if (trace_sched_set_need_resched_tp_enabled() && !(old_flags & (1 << tif)))
> +		trace_call__sched_set_need_resched_tp(curr, cpu_of(rq), tif);
> +
> +	return !(old_flags & _TIF_POLLING_NRFLAG);
>  }
>  
>  /*
> @@ -1076,8 +1083,11 @@ static bool set_nr_if_polling(struct task_struct *p)
>  }
>  
>  #else
> -static inline bool set_nr_and_not_polling(struct thread_info *ti, int tif)
> +static inline bool set_nr_and_not_polling(struct rq *rq, int tif)
>  {
> +	struct task_struct *curr = rq->curr;
> +	struct thread_info *ti = task_thread_info(curr);
> +
>  	set_ti_thread_flag(ti, tif);
>  	return true;
>  }

This !POLLING thing also needs tracing, no?

> @@ -1202,15 +1212,17 @@ static void __resched_curr(struct rq *rq, int tif)
>  
>  	cpu = cpu_of(rq);
>  
> -	trace_sched_set_need_resched_tp(curr, cpu, tif);
>  	if (cpu == smp_processor_id()) {
> -		set_ti_thread_flag(cti, tif);
> +		int set = test_and_set_ti_thread_flag(cti, tif);
> +
> +		if (trace_sched_set_need_resched_tp_enabled() && !set)
> +			trace_call__sched_set_need_resched_tp(curr, cpu, tif);
>  		if (tif == TIF_NEED_RESCHED)
>  			set_preempt_need_resched();
>  		return;
>  	}
>  
> -	if (set_nr_and_not_polling(cti, tif)) {
> +	if (set_nr_and_not_polling(rq, tif)) {
>  		if (tif == TIF_NEED_RESCHED)
>  			smp_send_reschedule(cpu);
>  	} else {
> @@ -1350,7 +1362,7 @@ static void wake_up_idle_cpu(int cpu)
>  	 * and testing of the above solutions didn't appear to report
>  	 * much benefits.
>  	 */
> -	if (set_nr_and_not_polling(task_thread_info(rq->idle), TIF_NEED_RESCHED))
> +	if (set_nr_and_not_polling(rq, TIF_NEED_RESCHED))
>  		smp_send_reschedule(cpu);
>  	else
>  		trace_sched_wake_idle_without_ipi(cpu);
> ---
> 
> > 
> > Thanks,
> > Gabriele
> > 
> 
> -- 
> Thanks and Regards,
> Prateek
>