Re: [futex] 8019ad13ef: will-it-scale.per_process_ops -97.8% regression

Thomas Gleixner
2020-03-09T09:35:04Z

Peter Zijlstra <peterz@infradead.org> writes:
> On Sun, Mar 08, 2020 at 07:07:17PM +0100, Thomas Gleixner wrote:
>> static struct futex_hash_bucket *hash_futex(union futex_key *key)
>> {
>> - u32 hash = jhash2((u32*)&key->both.word,
>> - (sizeof(key->both.word)+sizeof(key->both.ptr))/4,
>> + u32 hash = jhash2((u32*)&key->both.ptr,
>> + (sizeof(key->both.ptr) + sizeof(key->both.word)) / 4,
>> key->both.offset);
>> return &futex_queues[hash & (futex_hashsize - 1)];
>> }
>
> Groan... I've gotta ask, why isn't that written like:
>
> u32 hash = jhash2((u32 *)key,
> offsetof(typeof(*key), offset) / 4
> key->both.offset);
>
> Or better yet:
>
> u32 hash = jhash((u32 *)key, sizeof(*key) / 4, 0);

Histerical raisins :)