From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Juri Lelli <juri.lelli@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>,
Boqun Feng <boqun.feng@gmail.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Davidlohr Bueso <dave@stgolabs.net>,
Mike Galbraith <efault@gmx.de>
Subject: [patch V3 64/64] locking/rtmutex: Add adaptive spinwait mechanism
Date: Thu, 05 Aug 2021 17:14:04 +0200 [thread overview]
Message-ID: <20210805153956.507589092@linutronix.de> (raw)
In-Reply-To: 20210805151300.330412127@linutronix.de
From: Steven Rostedt <rostedt@goodmis.org>
Going to sleep when locks are contended can be quite inefficient when the
contention time is short and the lock owner is running on a different CPU.
The MCS mechanism cannot be used because MCS is strictly FIFO ordered while
for rtmutex based locks the waiter ordering is priority based.
Provide a simple adaptive spinwait mechanism which currently restricts the
spinning to the top priority waiter.
[ tglx: Provide a contemporary changelog ]
Originally-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
V3: Fold the extension for regular sleeping locks and add the missing spin
wait checks (PeterZ)
---
kernel/locking/rtmutex.c | 59 +++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 57 insertions(+), 2 deletions(-)
---
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -8,6 +8,11 @@
* Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
* Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
* Copyright (C) 2006 Esben Nielsen
+ * Adaptive Spinlocks:
+ * Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
+ * and Peter Morreale,
+ * Adaptive Spinlocks simplification:
+ * Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <srostedt@redhat.com>
*
* See Documentation/locking/rt-mutex-design.rst for details.
*/
@@ -1278,6 +1283,44 @@ static __always_inline void __rt_mutex_u
rt_mutex_slowunlock(lock);
}
+#ifdef CONFIG_SMP
+/*
+ * Note that owner is a speculative pointer and dereferencing relies
+ * on rcu_read_lock() and the check against the lock owner.
+ */
+static bool rtmutex_adaptive_spinwait(struct rt_mutex_base *lock,
+ struct task_struct *owner)
+{
+ bool res = true;
+
+ rcu_read_lock();
+ for (;;) {
+ /* Owner changed. Trylock again */
+ if (owner != rt_mutex_owner(lock))
+ break;
+ /*
+ * Ensure that owner->on_cpu is dereferenced _after_
+ * checking the above to be valid.
+ */
+ barrier();
+ if (!owner->on_cpu || need_resched() ||
+ vcpu_is_preempted(task_cpu(owner))) {
+ res = false;
+ break;
+ }
+ cpu_relax();
+ }
+ rcu_read_unlock();
+ return res;
+}
+#else
+static bool rtmutex_adaptive_spinwait(struct rt_mutex_base *lock,
+ struct task_struct *owner)
+{
+ return false;
+}
+#endif
+
#ifdef RT_MUTEX_BUILD_MUTEX
/*
* Functions required for:
@@ -1362,6 +1405,7 @@ static int __sched rt_mutex_slowlock_blo
struct rt_mutex_waiter *waiter)
{
struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
+ struct task_struct *owner;
int ret = 0;
for (;;) {
@@ -1384,9 +1428,14 @@ static int __sched rt_mutex_slowlock_blo
break;
}
+ if (waiter == rt_mutex_top_waiter(lock))
+ owner = rt_mutex_owner(lock);
+ else
+ owner = NULL;
raw_spin_unlock_irq(&lock->wait_lock);
- schedule();
+ if (!owner || !rtmutex_adaptive_spinwait(lock, owner))
+ schedule();
raw_spin_lock_irq(&lock->wait_lock);
set_current_state(state);
@@ -1542,6 +1591,7 @@ static __always_inline int __rt_mutex_lo
static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
{
struct rt_mutex_waiter waiter;
+ struct task_struct *owner;
lockdep_assert_held(&lock->wait_lock);
@@ -1560,9 +1610,14 @@ static void __sched rtlock_slowlock_lock
if (try_to_take_rt_mutex(lock, current, &waiter))
break;
+ if (&waiter == rt_mutex_top_waiter(lock))
+ owner = rt_mutex_owner(lock);
+ else
+ owner = NULL;
raw_spin_unlock_irq(&lock->wait_lock);
- schedule_rtlock();
+ if (!owner || !rtmutex_adaptive_spinwait(lock, owner))
+ schedule_rtlock();
raw_spin_lock_irq(&lock->wait_lock);
set_current_state(TASK_RTLOCK_WAIT);
next prev parent reply other threads:[~2021-08-05 15:46 UTC|newest]
Thread overview: 79+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-05 15:13 [patch V3 00/64] locking, sched: The PREEMPT-RT locking infrastructure Thomas Gleixner
2021-08-05 15:13 ` [patch V3 01/64] sched: Split out the wakeup state check Thomas Gleixner
2021-08-05 15:13 ` [patch V3 02/64] sched: Introduce TASK_RTLOCK_WAIT Thomas Gleixner
2021-08-05 15:13 ` [patch V3 03/64] sched: Reorganize current::__state helpers Thomas Gleixner
2021-08-05 15:13 ` [patch V3 04/64] sched: Prepare for RT sleeping spin/rwlocks Thomas Gleixner
2021-08-05 15:13 ` [patch V3 05/64] sched: Rework the __schedule() preempt argument Thomas Gleixner
2021-08-05 15:13 ` [patch V3 06/64] sched: Provide schedule point for RT locks Thomas Gleixner
2021-08-05 15:13 ` [patch V3 07/64] sched/wake_q: Provide WAKE_Q_HEAD_INITIALIZER Thomas Gleixner
2021-08-05 15:13 ` [patch V3 08/64] media/atomisp: Use lockdep instead of *mutex_is_locked() Thomas Gleixner
2021-08-05 15:13 ` [patch V3 09/64] rtmutex: Remove rt_mutex_is_locked() Thomas Gleixner
2021-08-05 15:13 ` [patch V3 10/64] rtmutex: Convert macros to inlines Thomas Gleixner
2021-08-05 15:13 ` [patch V3 11/64] rtmutex: Switch to try_cmpxchg() Thomas Gleixner
2021-08-05 15:13 ` [patch V3 12/64] rtmutex: Split API and implementation Thomas Gleixner
2021-08-05 15:13 ` [patch V3 13/64] rtmutex: Split out the inner parts of struct rtmutex Thomas Gleixner
2021-08-05 15:13 ` [patch V3 14/64] locking/rtmutex: Provide rt_mutex_slowlock_locked() Thomas Gleixner
2021-08-05 15:13 ` [patch V3 15/64] rtmutex: Provide rt_mutex_base_is_locked() Thomas Gleixner
2021-08-08 20:41 ` Davidlohr Bueso
2021-08-09 10:18 ` Thomas Gleixner
2021-08-05 15:13 ` [patch V3 16/64] locking: Add base code for RT rw_semaphore and rwlock Thomas Gleixner
2021-08-05 15:13 ` [patch V3 17/64] locking/rwsem: Add rtmutex based R/W semaphore implementation Thomas Gleixner
2021-08-05 15:13 ` [patch V3 18/64] locking/rtmutex: Add wake_state to rt_mutex_waiter Thomas Gleixner
2021-08-05 15:13 ` [patch V3 19/64] locking/rtmutex: Provide rt_wake_q and helpers Thomas Gleixner
2021-08-05 15:13 ` [patch V3 20/64] locking/rtmutex: Use rt_mutex_wake_q_head Thomas Gleixner
2021-08-05 15:13 ` [patch V3 21/64] locking/rtmutex: Prepare RT rt_mutex_wake_q for RT locks Thomas Gleixner
2021-08-05 15:13 ` [patch V3 22/64] locking/rtmutex: Guard regular sleeping locks specific functions Thomas Gleixner
2021-08-05 15:13 ` [patch V3 23/64] locking/spinlock: Split the lock types header Thomas Gleixner
2021-08-05 15:13 ` [patch V3 24/64] locking/rtmutex: Prevent future include recursion hell Thomas Gleixner
2021-08-05 15:13 ` [patch V3 25/64] locking/lockdep: Reduce includes in debug_locks.h Thomas Gleixner
2021-08-05 15:13 ` [patch V3 26/64] rbtree: Split out the rbtree type definitions Thomas Gleixner
2021-08-05 15:13 ` [patch V3 27/64] locking/rtmutex: Include only rbtree types Thomas Gleixner
2021-08-05 15:13 ` [patch V3 28/64] locking/spinlock: Provide RT specific spinlock type Thomas Gleixner
2021-08-05 15:13 ` [patch V3 29/64] locking/spinlock: Provide RT variant header Thomas Gleixner
2021-08-05 15:13 ` [patch V3 30/64] locking/rtmutex: Provide the spin/rwlock core lock function Thomas Gleixner
2021-08-05 15:13 ` [patch V3 31/64] locking/spinlock: Provide RT variant Thomas Gleixner
2021-08-05 15:13 ` [patch V3 32/64] locking/rwlock: " Thomas Gleixner
2021-08-05 15:13 ` [patch V3 33/64] locking/mutex: Consolidate core headers Thomas Gleixner
2021-08-05 15:13 ` [patch V3 34/64] locking/mutex: Move waiter to core header Thomas Gleixner
2021-08-05 15:13 ` [patch V3 35/64] locking/ww_mutex: Move ww_mutex declarations into ww_mutex.h Thomas Gleixner
2021-08-05 15:13 ` [patch V3 36/64] locking/mutex: Make mutex::wait_lock raw Thomas Gleixner
2021-08-05 15:13 ` [patch V3 37/64] locking/ww_mutex: Simplify lockdep annotation Thomas Gleixner
2021-08-05 15:13 ` [patch V3 38/64] locking/ww_mutex: Gather mutex_waiter initialization Thomas Gleixner
2021-08-05 15:13 ` [patch V3 39/64] locking/ww_mutex: Split up ww_mutex_unlock() Thomas Gleixner
2021-08-05 15:13 ` [patch V3 40/64] locking/ww_mutex: Split W/W implementation logic Thomas Gleixner
2021-08-05 15:13 ` [patch V3 41/64] locking/ww_mutex: Remove __sched annotation Thomas Gleixner
2021-08-05 15:13 ` [patch V3 42/64] locking/ww_mutex: Abstract waiter iteration Thomas Gleixner
2021-08-05 15:13 ` [patch V3 43/64] locking/ww_mutex: Abstract waiter enqueueing Thomas Gleixner
2021-08-05 15:13 ` [patch V3 44/64] locking/ww_mutex: Abstract mutex accessors Thomas Gleixner
2021-08-05 15:13 ` [patch V3 45/64] locking/ww_mutex: Abstract mutex types Thomas Gleixner
2021-08-05 15:13 ` [patch V3 46/64] locking/ww_mutex: Abstract internal lock access Thomas Gleixner
2021-08-05 15:13 ` [patch V3 47/64] locking/ww_mutex: Implement rt_mutex accessors Thomas Gleixner
2021-08-05 15:13 ` [patch V3 48/64] locking/ww_mutex: Add RT priority to W/W order Thomas Gleixner
2021-08-06 10:48 ` Peter Zijlstra
2021-08-06 11:50 ` Thomas Gleixner
2021-08-05 15:13 ` [patch V3 49/64] locking/ww_mutex: Add rt_mutex based lock type and accessors Thomas Gleixner
2021-08-05 15:13 ` [patch V3 50/64] locking/rtmutex: Extend the rtmutex core to support ww_mutex Thomas Gleixner
2021-08-06 11:00 ` Peter Zijlstra
2021-08-06 11:19 ` Thomas Gleixner
2021-08-06 13:48 ` Peter Zijlstra
2021-08-07 20:07 ` Thomas Gleixner
2021-08-05 15:13 ` [patch V3 51/64] locking/ww_mutex: Implement rtmutex based ww_mutex API functions Thomas Gleixner
2021-08-05 15:13 ` [patch V3 52/64] locking/rtmutex: Add mutex variant for RT Thomas Gleixner
2021-08-05 15:13 ` [patch V3 53/64] lib/test_lockup: Adapt to changed variables Thomas Gleixner
2021-08-05 15:13 ` [patch V3 54/64] futex: Validate waiter correctly in futex_proxy_trylock_atomic() Thomas Gleixner
2021-08-05 15:13 ` [patch V3 55/64] futex: Cleanup stale comments Thomas Gleixner
2021-08-05 15:13 ` [patch V3 56/64] futex: Correct the number of requeued waiters for PI Thomas Gleixner
2021-08-08 17:05 ` Davidlohr Bueso
2021-08-09 8:18 ` Thomas Gleixner
2021-08-09 10:52 ` Thomas Gleixner
2021-08-05 15:13 ` [patch V3 57/64] futex: Restructure futex_requeue() Thomas Gleixner
2021-08-05 15:13 ` [patch V3 58/64] futex: Clarify comment in futex_requeue() Thomas Gleixner
2021-08-08 18:43 ` Davidlohr Bueso
2021-08-09 8:18 ` Thomas Gleixner
2021-08-05 15:13 ` [patch V3 59/64] futex: Simplify handle_early_requeue_pi_wakeup() Thomas Gleixner
2021-08-05 15:14 ` [patch V3 60/64] futex: Prevent requeue_pi() lock nesting issue on RT Thomas Gleixner
2021-08-05 15:14 ` [patch V3 61/64] rtmutex: Prevent lockdep false positive with PI futexes Thomas Gleixner
2021-08-05 15:14 ` [patch V3 62/64] preempt: Adjust PREEMPT_LOCK_OFFSET for RT Thomas Gleixner
2021-08-05 15:14 ` [patch V3 63/64] locking/rtmutex: Implement equal priority lock stealing Thomas Gleixner
2021-08-05 15:14 ` Thomas Gleixner [this message]
2021-08-09 20:28 ` [patch V3 64/64] locking/rtmutex: Add adaptive spinwait mechanism Davidlohr Bueso
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