linux-kernel - Re: [PATCH v2 4/5] locking/lockdep: Make class->ops a percpu counter

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Date:   Wed, 3 Oct 2018 10:24:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/5] locking/lockdep: Make class->ops a percpu counter

On Wed, Oct 03, 2018 at 09:54:46AM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Tue, Oct 02, 2018 at 04:19:19PM -0400, Waiman Long wrote:
> > > +DEFINE_PER_CPU(unsigned long [MAX_LOCKDEP_KEYS], lock_class_ops);
> > 
> > > @@ -179,9 +181,30 @@ DECLARE_PER_CPU(struct lockdep_stats, lockdep_stats);
> > >  	}								\
> > >  	__total;							\
> > >  })
> > > +
> > > +static inline void debug_class_ops_inc(struct lock_class *class)
> > > +{
> > > +	int idx;
> > > +
> > > +	idx = class - lock_classes;
> > > +	__this_cpu_inc(lock_class_ops[idx]);
> > > +}
> > > +
> > > +static inline unsigned long debug_class_ops_read(struct lock_class *class)
> > > +{
> > > +	int idx, cpu;
> > > +	unsigned long ops = 0;
> > > +
> > > +	idx = class - lock_classes;
> > > +	for_each_possible_cpu(cpu)
> > > +		ops += per_cpu(lock_class_ops[idx], cpu);
> > > +	return ops;
> > > +}
> > 
> > Would it make sense to stick that in struct lockdep_stats ?
> > 
> > A little something like:
> > 
> > struct lockdep_stats {
> > 	/* ... */
> > 	int	lock_class_ops[MAX_LOCKDEP_KEYS];
> > };
> 
> Did you shrink the 'long' to 'int' intentionally?

nah, was because all of lockdep_stats is int and I didn't pay much
attention.