Re: [PATCH v5 3/3] sched/cputime: Add steal time support to full dynticks CPU time accounting

[Rik van Riel <riel@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 929 bytes --]

On Wed, 2016-06-08 at 11:05 +0800, Wanpeng Li wrote:
> 
> @@ -681,12 +681,17 @@ static cputime_t vtime_delta(struct task_struct
> *tsk)
>  static cputime_t get_vtime_delta(struct task_struct *tsk)
>  {
>  	unsigned long now = READ_ONCE(jiffies);
> -	unsigned long delta = now - tsk->vtime_snap;
> +	cputime_t delta_time, steal_time;
>  
> +	steal_time =
> jiffies_to_cputime(steal_account_process_tick());
> +	delta_time = jiffies_to_cputime(now - tsk->vtime_snap);
>  	WARN_ON_ONCE(tsk->vtime_snap_whence == VTIME_INACTIVE);
>  	tsk->vtime_snap = now;
>  
> -	return jiffies_to_cputime(delta);
> +	if (steal_time < delta_time)
> +		delta_time -= steal_time;
> +
> +	return delta_time;
>  }

This isn't right.

If steal_time is equal to or larger than delta_time,
get_vtime_delta needs to return 0, not delta_time.

Otherwise the same time will be counted twice.

-- 
All rights reversed

[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 473 bytes --]