MINOR: lb/chash: use a read lock in chash_get_server_hash()

When using a low hash-balance-factor value, it's possible to loop
many times trying to find the best server. Figures in the order of
100-300 times were observed for 1000 servers with a factor of 101
(which seems a bit excessive for such a large farm). Given that
there's nothing in that function that prevents multiple threads
from working in parallel, let's switch to a read lock. Tests on
8 threads show roughly a 2% performance increase with this.

diff --git a/src/lb_chash.c b/src/lb_chash.c
index a37a40ff2e09ad3796e315b2049235cab6b16a7c..709105c0e7b707744751adc747996192fa6798bf 100644 (file)
--- a/src/lb_chash.c
+++ b/src/lb_chash.c
@@ -324,7 +324,7 @@ struct server *chash_get_server_hash(struct proxy *p, unsigned int hash, const s
        unsigned int dn, dp;
        int loop;
 
-       HA_RWLOCK_WRLOCK(LBPRM_LOCK, &p->lbprm.lock);
+       HA_RWLOCK_RDLOCK(LBPRM_LOCK, &p->lbprm.lock);
 
        if (p->srv_act)
                root = &p->lbprm.chash.act;
@@ -379,7 +379,7 @@ struct server *chash_get_server_hash(struct proxy *p, unsigned int hash, const s
        }
 
  out:
-       HA_RWLOCK_WRUNLOCK(LBPRM_LOCK, &p->lbprm.lock);
+       HA_RWLOCK_RDUNLOCK(LBPRM_LOCK, &p->lbprm.lock);
        return nsrv;
 }