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From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Mike Kravetz <mike.kravetz@oracle.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, Davidlohr Bueso <dave@stgolabs.net>,
	Waiman Long <longman@redhat.com>
Subject: [PATCH 4/5] locking/rwsem: Enable timeout check when staying in the OSQ
Date: Wed, 11 Sep 2019 16:05:36 +0100
Message-ID: <20190911150537.19527-5-longman@redhat.com> (raw)
In-Reply-To: <20190911150537.19527-1-longman@redhat.com>

Use the break function allowed by the new osq_lock() to enable early
break from the OSQ when a timeout value is specified and expiration
time has been reached.

Signed-off-by: Waiman Long <longman@redhat.com>
---
 kernel/locking/rwsem.c | 35 +++++++++++++++++++++++++++++++----
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index c15926ecb21e..78708097162a 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -794,23 +794,50 @@ static inline u64 rwsem_rspin_threshold(struct rw_semaphore *sem)
 	return sched_clock() + delta;
 }
 
+struct rwsem_break_arg {
+	u64 timeout;
+	int loopcnt;
+};
+
+static bool rwsem_osq_break(void *brk_arg)
+{
+	struct rwsem_break_arg *arg = brk_arg;
+
+	arg->loopcnt++;
+	/*
+	 * Check sched_clock() only once every 256 iterations.
+	 */
+	if (!(arg->loopcnt++ & 0xff) && (sched_clock() >= arg->timeout))
+		return true;
+	return false;
+}
+
 static bool rwsem_optimistic_spin(struct rw_semaphore *sem, bool wlock,
 				  ktime_t timeout)
 {
-	bool taken = false;
+	bool taken = false, locked;
 	int prev_owner_state = OWNER_NULL;
 	int loop = 0;
 	u64 rspin_threshold = 0, curtime;
+	struct rwsem_break_arg break_arg;
 	unsigned long nonspinnable = wlock ? RWSEM_WR_NONSPINNABLE
 					   : RWSEM_RD_NONSPINNABLE;
 
 	preempt_disable();
 
 	/* sem->wait_lock should not be held when doing optimistic spinning */
-	if (!osq_lock(&sem->osq, NULL, NULL))
-		goto done;
+	if (timeout) {
+		break_arg.timeout = ktime_to_ns(timeout);
+		break_arg.loopcnt = 0;
+		locked = osq_lock(&sem->osq, rwsem_osq_break, &break_arg);
+		curtime = sched_clock();
+	} else {
+		locked = osq_lock(&sem->osq, NULL, NULL);
+		curtime = 0;
+	}
 
-	curtime = timeout ? sched_clock() : 0;
+	if (!locked)
+		goto done;
 
 	/*
 	 * Optimistically spin on the owner field and attempt to acquire the
-- 
2.18.1


  parent reply index

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-11 15:05 [PATCH 0/5] hugetlbfs: Disable PMD sharing for large systems Waiman Long
2019-09-11 15:05 ` [PATCH 1/5] locking/rwsem: Add down_write_timedlock() Waiman Long
2019-09-11 15:05 ` [PATCH 2/5] locking/rwsem: Enable timeout check when spinning on owner Waiman Long
2019-09-11 15:05 ` [PATCH 3/5] locking/osq: Allow early break from OSQ Waiman Long
2019-09-11 15:05 ` Waiman Long [this message]
2019-09-11 15:05 ` [PATCH 5/5] hugetlbfs: Limit wait time when trying to share huge PMD Waiman Long
2019-09-11 15:14   ` Matthew Wilcox
2019-09-11 15:44     ` Waiman Long
2019-09-11 17:03       ` Mike Kravetz
2019-09-11 17:15         ` Waiman Long
2019-09-11 17:22           ` Qian Cai
2019-09-11 17:28           ` Waiman Long
2019-09-11 16:01   ` Qian Cai
2019-09-11 16:34     ` Waiman Long
2019-09-11 19:42       ` Qian Cai
2019-09-11 20:54         ` Waiman Long
2019-09-11 21:57           ` Qian Cai
2019-09-11 19:57   ` Matthew Wilcox
2019-09-11 20:51     ` Waiman Long
2019-09-12  3:26   ` Mike Kravetz
2019-09-12  3:41     ` Matthew Wilcox
2019-09-12  4:40       ` Davidlohr Bueso
2019-09-16 13:53         ` Waiman Long
2019-09-12  9:06     ` Waiman Long
2019-09-12 16:43       ` Mike Kravetz
2019-09-13 18:23         ` Waiman Long
2019-09-13  1:50 ` [PATCH 0/5] hugetlbfs: Disable PMD sharing for large systems Dave Chinner
2019-09-25  8:35   ` Peter Zijlstra

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