Re: [RFC PATCH] tg: count the sum wait time of an task group

[çè]

Hi, Peter

On 2018/7/2 äå8:03, Peter Zijlstra wrote:
> On Mon, Jul 02, 2018 at 03:29:39PM +0800, çè wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1866e64..ef82ceb 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -862,6 +862,7 @@ static void update_curr_fair(struct rq *rq)
> >   static inline void
> >   update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
> >   {
> > +	struct task_group *tg;
> >   	struct task_struct *p;
> >   	u64 delta;
> >
> > @@ -882,6 +883,9 @@ static void update_curr_fair(struct rq *rq)
> >   			return;
> >   		}
> >   		trace_sched_stat_wait(p, delta);
> > +	} else {
> > +		tg = group_cfs_rq(se)->tg;
> > +		__schedstat_add(tg->wait_sum, delta);
> >   	}
>
> You're joking right? This patch is both broken and utterly insane.
>
> You're wanting to update an effectively global variable for every
> schedule action (and its broken because it is without any serialization
> or atomics).

Thanks for the reply and sorry for the thoughtless, I'll rewrite
the code to make it per-cpu variable, then assemble the results
on show.

Regards,
Michael Wang


> NAK