Re: [PATCH 2/3] sched, timer: Use atomics for thread_group_cputimer to improve scalability

[Preeti U Murthy <preeti@linux.vnet.ibm.com>]

On 04/15/2015 04:39 AM, Jason Low wrote:
>  /*
> @@ -885,11 +890,8 @@ static void check_thread_timers(struct task_struct *tsk,
>  static void stop_process_timers(struct signal_struct *sig)
>  {
>  	struct thread_group_cputimer *cputimer = &sig->cputimer;
> -	unsigned long flags;
> 
> -	raw_spin_lock_irqsave(&cputimer->lock, flags);
> -	cputimer->running = 0;
> -	raw_spin_unlock_irqrestore(&cputimer->lock, flags);
> +	WRITE_ONCE(cputimer->running, 0);

Why do a WRITE_ONCE() here ? Maybe you should explicitly mention this
through a comment like Steven pointed out about all
WRITE/READ/ACCESS_ONCE() usage.

Regards
Preeti U Murthy
>  }
> 
>  static u32 onecputick;
> @@ -1114,9 +1116,7 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
>  	if (sig->cputimer.running) {
>  		struct task_cputime group_sample;
> 
> -		raw_spin_lock(&sig->cputimer.lock);
> -		group_sample = sig->cputimer.cputime;
> -		raw_spin_unlock(&sig->cputimer.lock);
> +		sample_group_cputimer(&group_sample, &sig->cputimer);
> 
>  		if (task_cputime_expired(&group_sample, &sig->cputime_expires))
>  			return 1;
>