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

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Date:   Wed, 3 Oct 2018 09:48:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     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 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];
};

and then use:

	debug_atomic_inc(lock_class_ops[idx]);