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Date: Tue, 2 Oct 2018 11:55:43 +0200 From: Ingo Molnar <mingo@...nel.org> To: Peter Zijlstra <peterz@...radead.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 4/5] locking/lockdep: Make class->ops a percpu counter * Peter Zijlstra <peterz@...radead.org> wrote: > On Fri, Sep 28, 2018 at 01:53:20PM -0400, Waiman Long wrote: > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > > index ca002c0..7a0ed1d 100644 > > --- a/kernel/locking/lockdep.c > > +++ b/kernel/locking/lockdep.c > > @@ -139,6 +139,7 @@ static inline int debug_locks_off_graph_unlock(void) > > */ > > unsigned long nr_lock_classes; > > static struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; > > +static DEFINE_PER_CPU(unsigned long [MAX_LOCKDEP_KEYS], lock_class_ops); > > > @@ -1387,11 +1391,15 @@ static inline int usage_match(struct lock_list *entry, void *bit) > > > > static void print_lock_class_header(struct lock_class *class, int depth) > > { > > - int bit; > > + int bit, cpu; > > + unsigned long ops = 0UL; > > + > > + for_each_possible_cpu(cpu) > > + ops += *per_cpu(class->pops, cpu); > > > > printk("%*s->", depth, ""); > > print_lock_name(class); > > - printk(KERN_CONT " ops: %lu", class->ops); > > + printk(KERN_CONT " ops: %lu", ops); > > printk(KERN_CONT " {\n"); > > > > for (bit = 0; bit < LOCK_USAGE_STATES; bit++) { > > That is an aweful lot of storage for a stupid number. Some archs > (sparc64) are bzImage size constrained and this will hurt them. > > Ingo, do you happen to remember what that number was good for? Just a spur of the moment statistics to satisfy curiousity, and it's useful to see how 'busy' a particular class is, right? > Can't we simply ditch it? We certainly could. Do we have roughly equivalent metrics to arrive at this number via other methods? Thanks, Ingo
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