Re: [RFC] [Patch 4/4] lock contention tracking slimmed down

[Martin Peschke <mp3@de.ibm.com>]

Peter Zijlstra wrote:
> On Fri, 2007-06-08 at 19:18 +0200, Martin Peschke wrote:
> > Peter Zijlstra wrote:
> > > On Fri, 2007-06-08 at 19:00 +0200, Martin Peschke wrote:
> > > > Peter Zijlstra wrote:
> > > > > I'm confused as to where the class->stat objects are initialised? Is
> > > > > that done in lock_stat_init()? If so, then you have a bug.
> > > > static struct lock_class lock_classes[MAX_LOCKDEP_KEYS];
> > > >
> > > > I assume this gets us class structures containing all zeros, doesn't it?
> > > > Then class->stat is zeros as well, which is handled by lib/statistics.
> > > > (In this case, data gathering hasn't been turned on yet, and statistic_inc()
> > > > and similar functions don't access other areas of struct statistic.)
> > > Who eventually calls percpu_alloc?
> > There is a small state machine calling percpu_alloc when users do
> >
> >     echo state=on > /debug/statistics/lockdep/definition
> >
> > So data gathering is off by default.
> >
> > It might make sense to allow "state=on" as a default. Then allocation would
> > be done in the context of statistic_attach().
>
> Right, the problem here is that you iterate over all_lock_classes once
> at init.
>
> Contrary to what the name might suggest, it are not all possible
> classes, just all active ones. So you'll only attach the classes which
> have been used up until the init point. All other classes used later
> will never be initialized.

Ah..

Do you know where a class is setup for first use?
I guess it is feasible to move statistic initialisation to that place.

Is there a place where a class becomes unused again?


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