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Date:      Wed, 14 Feb 2018 20:37:34 +0000 (UTC)
From:      Mateusz Guzik <mjg@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r329276 - head/sys/kern
Message-ID:  <201802142037.w1EKbYuf011260@repo.freebsd.org>
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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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