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

[Balbir Singh <balbir@in.ibm.com>]

Andrew Morton wrote:
> On Fri, 09 Jun 2006 16:21:46 +0530
> Balbir Singh <balbir@in.ibm.com> wrote:
>
>
> > Andrew Morton wrote:
> >
> > > On Fri, 09 Jun 2006 03:41:04 -0400
> > > Shailabh Nagar <nagar@watson.ibm.com> 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?

Another option is to get the package to define their own taskstats genetlink 
attribute and fill it up in taskstats_exit_send(). This would be similar to
TASKSTATS_TYPE_AGGR_PID/TGID.

They can make this attribute independent of the taskstats structure and fill
it based on their policy (per-pid or per-tgid). But the current interface
users like CSA want to build on top of the taskstats structure.

> 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?


--

	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs
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