On Mon, May 23, 2016 at 23:28:27 +0300, Sergey Fedorov wrote:
> What if we turn qht::lock into a mutex and change the function as follows:
>
> static inline
> struct qht_bucket *qht_bucket_lock__no_stale(struct qht *ht,
> uint32_t hash,
> struct qht_map
> **pmap)
> {
> struct qht_bucket *b;
> struct qht_map *map;
>
> map = atomic_rcu_read(&ht->map);
> b = qht_map_to_bucket(map, hash);
>
> qemu_spin_lock(&b->lock);
> /* 'ht->map' access is serialized by 'b->lock' here */
> if (likely(map == ht->map)) {
> /* no resize in progress; we're done */
> *pmap = map;
> return b;
> }
> qemu_spin_unlock(&b->lock);
>
> /* resize in progress; retry grabbing 'ht->lock' */
> qemu_mutex_lock(&ht->lock);
> b = qht_map_to_bucket(ht->map, hash);
> *pmap = ht->map;
> qemu_spin_lock(&b->lock);
> qemu_mutex_unlock(&ht->lock);
>
> return b;
> }
>
>
> With this implementation we could:
> (1) get rid of qht_map::stale
> (2) don't waste cycles waiting for resize to complete
I'll include this in v6.
Thanks,
Emilio
