On 3/30/16, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Wed, Mar 30, 2016 at 11:36:59AM +0200, Peter Zijlstra wrote: >> Furthermore, our hash function has definite room for improvement. > > After a bit of reading, using a 'strong' PRNG as base for a hash > function seems generally suggested. > > --- > kernel/locking/lockdep.c | 19 +++++++++++++++---- > 1 file changed, 15 insertions(+), 4 deletions(-) > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 53ab2f85d77e..0f7dba4144d6 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -308,10 +308,21 @@ static struct hlist_head > chainhash_table[CHAINHASH_SIZE]; > * It's a 64-bit hash, because it's important for the keys to be > * unique. > */ > -#define iterate_chain_key(key1, key2) \ > - (((key1) << MAX_LOCKDEP_KEYS_BITS) ^ \ > - ((key1) >> (64-MAX_LOCKDEP_KEYS_BITS)) ^ \ > - (key2)) > + > +/* https://en.wikipedia.org/wiki/Xorshift#xorshift.2A */ > +#define UINT64_C(x) x##ULL > +static inline u64 xorshift64star(u64 x) > +{ > + x ^= x >> 12; // a > + x ^= x << 25; // b > + x ^= x >> 27; // c > + return x * UINT64_C(2685821657736338717); > +} > + > +static inline u64 iterate_chain_key(u64 hash, u64 class_idx) > +{ > + return xorshift64star(hash ^ class_idx); > +} > > void lockdep_off(void) > { > You dropped this implementation and the below is a different approach? "locking/lockdep: Use __jhash_mix() for iterate_chain_key()" - Sedat - [1] http://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?h=locking/core&id=724e66913097c2eba029b06dcd05c5a2be78d466 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
