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

Jay Lan
2006-06-29T19:33:10Z

Andrew Morton wrote:
> On Thu, 29 Jun 2006 09:44:08 -0700
> Paul Jackson <pj@sgi.com> 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.