linux-kernel - Re: [PATCH v3 03/15] lockdep: Refactor lookup_chain

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Date:   Mon, 19 Sep 2016 12:05:58 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     Nilay Vaish <nilayvaish@...il.com>
Cc:     peterz@...radead.org, mingo@...nel.org, tglx@...utronix.de,
        walken@...gle.com, boqun.feng@...il.com, kirill@...temov.name,
        Linux Kernel list <linux-kernel@...r.kernel.org>,
        linux-mm@...ck.org, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, npiggin@...il.com
Subject: Re: [PATCH v3 03/15] lockdep: Refactor lookup_chain_cache()

On Thu, Sep 15, 2016 at 10:33:46AM -0500, Nilay Vaish wrote:
> On 13 September 2016 at 04:45, Byungchul Park <byungchul.park@....com> wrote:
> > @@ -2215,6 +2178,75 @@ cache_hit:
> >         return 1;
> >  }
> >
> > +/*
> > + * Look up a dependency chain.
> > + */
> > +static inline struct lock_chain *lookup_chain_cache(u64 chain_key)
> > +{
> > +       struct hlist_head *hash_head = chainhashentry(chain_key);
> > +       struct lock_chain *chain;
> > +
> > +       /*
> > +        * We can walk it lock-free, because entries only get added
> > +        * to the hash:
> > +        */
> > +       hlist_for_each_entry_rcu(chain, hash_head, entry) {
> > +               if (chain->chain_key == chain_key) {
> > +                       debug_atomic_inc(chain_lookup_hits);
> > +                       return chain;
> > +               }
> > +       }
> > +       return NULL;
> > +}
> 
> Byungchul,  do you think we should increment chain_lookup_misses
> before returning NULL from the above function?

Hello,

No, I don't think so.
It will be done in add_chain_cache().

Thank you,
Byungchul

> 
> --
> Nilay