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

[Andrew Morton]

On Fri, 09 Jun 2006 16:21:46 +0530
Balbir Singh <balbir@xxxxxxxxxx> wrote:

> Andrew Morton wrote:
> > On Fri, 09 Jun 2006 03:41:04 -0400
> > Shailabh Nagar <nagar@xxxxxxxxxxxxxx> wrote:
> > 
> > 
> >>Hence, this patch introduces a configuration parameter
> >>	/sys/kernel/taskstats_tgid_exit
> >>through which a privileged user can turn on/off sending of per-tgid stats on
> >>task exit.
> > 
> > 
> > That seems a bit clumsy.  What happens if one consumer wants the per-tgid
> > stats and another does not?
> 
> For all subsystems that re-use the taskstats structure from the exit path,
> we have the issue that you mentioned. Thats because several statistics co-exist
> in the same structure. These subsystems can keep their tgid-stats empty by not
> filling up anything in fill_tgid() or using this patch to selectively enable/disable
> tgid stats.
> 
> For other subsystems, they could pass tgidstats as NULL to taskstats_exit_send().
> 

I don't understand.  If a subsystem exists then it fills in its slots in
the taskstats structure, doesn't it?

No other subsystem needs a global knob, does it?

You see the problem - if one userspace package wants the tgid-stats and
another concurrently-running one does now, what do we do?  Just leave it
enabled and run a bit slower?

If so, how much slower?  Your changelog says some potential users don't
need the tgid-stats, but so what?  I assume this patch is a performance
thing?  If so, has it been quantified?

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