Author: mjg
Date: Wed Feb 14 20:37:33 2018
New Revision: 329276
URL: https://svnweb.freebsd.org/changeset/base/329276

Log:
  rwlock: diff-reduction of runlock compared to sx sunlock

Modified:
  head/sys/kern/kern_rwlock.c

Modified: head/sys/kern/kern_rwlock.c
==============================================================================
--- head/sys/kern/kern_rwlock.c Wed Feb 14 20:26:09 2018        (r329275)
+++ head/sys/kern/kern_rwlock.c Wed Feb 14 20:37:33 2018        (r329276)
@@ -760,22 +760,19 @@ __rw_runlock_hard(struct rwlock *rw, struct thread *td
        if (SCHEDULER_STOPPED())
                return;
 
+       if (__rw_runlock_try(rw, td, &v))
+               goto out_lockstat;
+
+       /*
+        * Ok, we know we have waiters and we think we are the
+        * last reader, so grab the turnstile lock.
+        */
+       turnstile_chain_lock(&rw->lock_object);
+       v = RW_READ_VALUE(rw);
        for (;;) {
                if (__rw_runlock_try(rw, td, &v))
                        break;
 
-               /*
-                * Ok, we know we have waiters and we think we are the
-                * last reader, so grab the turnstile lock.
-                */
-               turnstile_chain_lock(&rw->lock_object);
-               v = RW_READ_VALUE(rw);
-retry_ts:
-               if (__rw_runlock_try(rw, td, &v)) {
-                       turnstile_chain_unlock(&rw->lock_object);
-                       break;
-               }
-
                v &= (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
                MPASS(v & RW_LOCK_WAITERS);
 
@@ -803,7 +800,7 @@ retry_ts:
                }
                v |= RW_READERS_LOCK(1);
                if (!atomic_fcmpset_rel_ptr(&rw->rw_lock, &v, setv))
-                       goto retry_ts;
+                       continue;
                if (LOCK_LOG_TEST(&rw->lock_object, 0))
                        CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
                            __func__, rw);
@@ -819,10 +816,11 @@ retry_ts:
                MPASS(ts != NULL);
                turnstile_broadcast(ts, queue);
                turnstile_unpend(ts, TS_SHARED_LOCK);
-               turnstile_chain_unlock(&rw->lock_object);
                td->td_rw_rlocks--;
                break;
        }
+       turnstile_chain_unlock(&rw->lock_object);
+out_lockstat:
        LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_READER);
 }
 
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