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

[Jay Lan]

Andrew Morton wrote:
> On Thu, 29 Jun 2006 09:44:08 -0700
> Paul Jackson <pj@xxxxxxx> wrote:
>
>
> > > You're probably correct on that model. However, it all depends on the actual
> > > workload. Are people who actually have large-CPU (>256) systems actually
> > > running fork()-heavy things like webservers on them, or are they running things
> > > like database servers and computations, which tend to have persistent
> > > processes?
> >
> > It may well be mostly as you say - the large-CPU systems not running
> > the fork() heavy jobs.
> >
> > Sooner or later, someone will want to run a fork()-heavy job on a
> > large-CPU system.  On a 1024 CPU system, it would apparently take
> > just 14 exits/sec/CPU to hit this bottleneck, if Jay's number of
> > 14000 applied.
> >
> > Chris Sturdivant's reply is reasonable -- we'll hit it sooner or later,
> > and deal with it then.
>
>
> I agree, and I'm viewing this as blocking the taskstats merge.  Because if
> this _is_ a problem then it's a big one because fixing it will be
> intrusive, and might well involve userspace-visible changes.
>
> The only ways I can see of fixing the problem generally are to either
>
> a) throw more CPU(s) at stats collection: allow userspace to register for
>    "stats generated by CPU N", then run a stats collection daemon on each
>    CPU or

Clearly this approach (or the per-cpuset as Paul suggested) can solve
large-CPU system issues. As technology advances, this _WILL_ become a
problem sooner or later.

However, taskstats header carries a version number. Would a change like
this too intrusive to add to a later version?

Regards,
 - jay


> b) make the kernel recognise when it's getting overloaded and switch to
>    some degraded mode where it stops trying to send all the data to
>    userspace - just send a summary, or a "we goofed" message or something.

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