Re: [Patch][RFC] Disabling per-tgid stats on task exit in taskstats

Andrew Morton
2006-06-23T23:47:53Z

On Fri, 23 Jun 2006 15:07:28 -0700
Jay Lan <jlan@engr.sgi.com> wrote:

> >> %ovhd of tgid on over off
> >> (higher is worse)
> >>
> >>Exit User Sys Elapsed
> >>Rate Time Time Time
> >>
> >>2283 25.76 649.41 -0.14
> >>1193 -10.53 88.81 -0.12
> >>963 -11.90 3.28 -0.10
> >>806 -8.54 -0.84 0.16
> >>694 -4.41 2.38 0.03
> >>
> >
> >Oh wow. Something's gone quadratic there.
> >
> It was due to a loop in fill_tgid() when per-TG stats
> data are assembled for netlink:
> do {
> rc = delayacct_add_tsk(stats, tsk);
> if (rc)
> break;
>
> } while_each_thread(first, tsk);
>
> and it is executed inside a lock.
> Fortunately single threaded appls do not hit this code.

Am I reading this right? We do that loop when each thread within the
thread group exits? How come?

Is there some better lock we can use in there? It only has to be
threadgroup-wide rather than kernel-wide.