[ANNOUNCE] v5.14-rc3-rt2v5.14-rc3-rt2-patches

Dear RT folks!

I'm pleased to announce the v5.14-rc3-rt2 patch set.

Changes since v5.14-rc3-rt1:

  - To cope with SLUB based hackbench regression adaptive spinning has
    been introduced for all rtmutex based locks. This improves the
    hackbench time significantly.

Known issues
     - netconsole triggers WARN.

     - The "Memory controller" (CONFIG_MEMCG) has been disabled.

The delta patch against v5.14-rc3-rt1 is appended below and can be found here:

     https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.14/incr/patch-5.14-rc3-rt1-rt2.patch.xz

You can get this release via the git tree at:

    git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git v5.14-rc3-rt2

The RT patch against v5.14-rc3 can be found here:

    https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.14/older/patch-5.14-rc3-rt2.patch.xz

The split quilt queue is available at:

    https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.14/older/patches-5.14-rc3-rt2.tar.xz

Sebastian

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

3 files changed, 138 insertions, 1 deletions

diff --git a/patches/Add_localversion_for_-RT_release.patch b/patches/Add_localversion_for_-RT_release.patch
index 0e6dbb0e3c10..d960d516454d 100644
--- a/patches/Add_localversion_for_-RT_release.patch
+++ b/patches/Add_localversion_for_-RT_release.patch
@@ -15,4 +15,4 @@ Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
 --- /dev/null
 +++ b/localversion-rt
 @@ -0,0 +1 @@
-+-rt1
++-rt2
diff --git a/patches/locking_rtmutex__Use_adaptive_spinwait_for_all_rtmutex_based_locks.patch b/patches/locking_rtmutex__Use_adaptive_spinwait_for_all_rtmutex_based_locks.patch
new file mode 100644
index 000000000000..9eaaacb4d463
--- /dev/null
+++ b/patches/locking_rtmutex__Use_adaptive_spinwait_for_all_rtmutex_based_locks.patch
@@ -0,0 +1,136 @@
+Subject: locking/rtmutex: Use adaptive spinwait for all rtmutex based locks
+From: Thomas Gleixner <tglx@linutronix.de>
+Date: Fri, 30 Jul 2021 11:58:42 +0200
+
+There is no reason to restrict adaptive spinwait to the rt mutex based
+'spinlocks'. Testing shows a 4x impromevemt for hackbench.
+
+Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
+---
+---
+ kernel/locking/rtmutex.c |   84 +++++++++++++++++++++++++----------------------
+ 1 file changed, 45 insertions(+), 39 deletions(-)
+
+--- a/kernel/locking/rtmutex.c
++++ b/kernel/locking/rtmutex.c
+@@ -1277,6 +1277,43 @@ 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) {
++			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:
+@@ -1361,6 +1398,7 @@ 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 (;;) {
+@@ -1383,9 +1421,14 @@ 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);
+@@ -1534,43 +1577,6 @@ static __always_inline int __rt_mutex_lo
+  * Functions required for spin/rw_lock substitution on RT kernels
+  */
+ 
+-#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 rtlock_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) {
+-			res = false;
+-			break;
+-		}
+-		cpu_relax();
+-	}
+-	rcu_read_unlock();
+-	return res;
+-}
+-#else
+-static bool rtlock_adaptive_spinwait(struct rt_mutex_base *lock,
+-				     struct task_struct *owner)
+-{
+-	return false;
+-}
+-#endif
+-
+ /**
+  * rtlock_slowlock_locked - Slow path lock acquisition for RT locks
+  * @lock:	The underlying rt mutex
+@@ -1603,7 +1609,7 @@ static void __sched rtlock_slowlock_lock
+ 			owner = NULL;
+ 		raw_spin_unlock_irq(&lock->wait_lock);
+ 
+-		if (!owner || !rtlock_adaptive_spinwait(lock, owner))
++		if (!owner || !rtmutex_adaptive_spinwait(lock, owner))
+ 			schedule_rtlock();
+ 
+ 		raw_spin_lock_irq(&lock->wait_lock);
diff --git a/patches/series b/patches/series
index 01044844a584..a1f95cf35d55 100644
--- a/patches/series
+++ b/patches/series
@@ -185,6 +185,7 @@ rtmutex__Prevent_lockdep_false_positive_with_PI_futexes.patch
 preempt__Adjust_PREEMPT_LOCK_OFFSET_for_RT.patch
 locking_rtmutex__Implement_equal_priority_lock_stealing.patch
 locking_rtmutex__Add_adaptive_spinwait_mechanism.patch
+locking_rtmutex__Use_adaptive_spinwait_for_all_rtmutex_based_locks.patch
 
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 # Locking: RT bits. Need review