From edcd591c77a48da753456f92daf8bb50fe9bac93 Mon Sep 17 00:00:00 2001
From: Jonathan Corbet <corbet@lwn.net>
Date: Mon, 7 Sep 2015 13:18:03 -0600
Subject: [PATCH 1/4] locking/static_keys: Fix a silly typo
Commit:
412758cb2670 ("jump label, locking/static_keys: Update docs")
introduced a typo that might as well get fixed.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150907131803.54c027e1@lwn.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
Documentation/static-keys.txt | 2 +-
include/linux/jump_label.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/Documentation/static-keys.txt b/Documentation/static-keys.txt
index f4cb0b2d5cd7..ec911583f6c5 100644
--- a/Documentation/static-keys.txt
+++ b/Documentation/static-keys.txt
@@ -16,7 +16,7 @@ The updated API replacements are:
DEFINE_STATIC_KEY_TRUE(key);
DEFINE_STATIC_KEY_FALSE(key);
static_key_likely()
-statick_key_unlikely()
+static_key_unlikely()
0) Abstract
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 7f653e8f6690..0684bd3a48fc 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -22,7 +22,7 @@
* DEFINE_STATIC_KEY_TRUE(key);
* DEFINE_STATIC_KEY_FALSE(key);
* static_key_likely()
- * statick_key_unlikely()
+ * static_key_unlikely()
*
* Jump labels provide an interface to generate dynamic branches using
* self-modifying code. Assuming toolchain and architecture support, if we
From 43b3f02899f74ae9914a39547cc5492156f0027a Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Fri, 4 Sep 2015 17:25:23 +0200
Subject: [PATCH 2/4] locking/qspinlock/x86: Fix performance regression under
unaccelerated VMs
Dave ran into horrible performance on a VM without PARAVIRT_SPINLOCKS
set and Linus noted that the test-and-set implementation was retarded.
One should spin on the variable with a load, not a RMW.
While there, remove 'queued' from the name, as the lock isn't queued
at all, but a simple test-and-set.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Dave Chinner <david@fromorbit.com>
Tested-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <Waiman.Long@hp.com>
Cc: stable@vger.kernel.org # v4.2+
Link: http://lkml.kernel.org/r/20150904152523.GR18673@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/qspinlock.h | 16 ++++++++++++----
include/asm-generic/qspinlock.h | 4 ++--
kernel/locking/qspinlock.c | 2 +-
3 files changed, 15 insertions(+), 7 deletions(-)
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 9d51fae1cba3..8dde3bdc4a05 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -39,15 +39,23 @@ static inline void queued_spin_unlock(struct qspinlock *lock)
}
#endif
-#define virt_queued_spin_lock virt_queued_spin_lock
+#define virt_spin_lock virt_spin_lock
-static inline bool virt_queued_spin_lock(struct qspinlock *lock)
+static inline bool virt_spin_lock(struct qspinlock *lock)
{
if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
return false;
- while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0)
- cpu_relax();
+ /*
+ * On hypervisors without PARAVIRT_SPINLOCKS support we fall
+ * back to a Test-and-Set spinlock, because fair locks have
+ * horrible lock 'holder' preemption issues.
+ */
+
+ do {
+ while (atomic_read(&lock->val) != 0)
+ cpu_relax();
+ } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
return true;
}
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index 83bfb87f5bf1..e2aadbc7151f 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -111,8 +111,8 @@ static inline void queued_spin_unlock_wait(struct qspinlock *lock)
cpu_relax();
}
-#ifndef virt_queued_spin_lock
-static __always_inline bool virt_queued_spin_lock(struct qspinlock *lock)
+#ifndef virt_spin_lock
+static __always_inline bool virt_spin_lock(struct qspinlock *lock)
{
return false;
}
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 337c8818541d..87e9ce6a63c5 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -289,7 +289,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
if (pv_enabled())
goto queue;
- if (virt_queued_spin_lock(lock))
+ if (virt_spin_lock(lock))
return;
/*
From a6b277857fd2c990bc208ca1958d3f34d26052f7 Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <peterz@infradead.org>
Date: Sat, 5 Sep 2015 16:55:05 +0200
Subject: [PATCH 3/4] locking/qspinlock/x86: Only emit the test-and-set
fallback when building guest support
Only emit the test-and-set fallback for Hypervisors lacking
PARAVIRT_SPINLOCKS support when building for guests.
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org # 4.2
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/qspinlock.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 8dde3bdc4a05..eaba08076030 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -39,8 +39,8 @@ static inline void queued_spin_unlock(struct qspinlock *lock)
}
#endif
+#ifdef CONFIG_PARAVIRT
#define virt_spin_lock virt_spin_lock
-
static inline bool virt_spin_lock(struct qspinlock *lock)
{
if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
@@ -59,6 +59,7 @@ static inline bool virt_spin_lock(struct qspinlock *lock)
return true;
}
+#endif /* CONFIG_PARAVIRT */
#include <asm-generic/qspinlock.h>
From 1975dbc276c6ab62230cf4f9df5ddc9ff0e0e473 Mon Sep 17 00:00:00 2001
From: Jonathan Corbet <corbet@lwn.net>
Date: Mon, 14 Sep 2015 17:11:05 -0600
Subject: [PATCH 4/4] locking/static_keys: Fix up the static keys documentation
Fix a few small mistakes in the static key documentation and
delete an unneeded sentence.
Suggested-by: Jason Baron <jbaron@akamai.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20150914171105.511e1e21@lwn.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
Documentation/static-keys.txt | 4 ++--
include/linux/jump_label.h | 10 ++++------
2 files changed, 6 insertions(+), 8 deletions(-)
diff --git a/Documentation/static-keys.txt b/Documentation/static-keys.txt
index ec911583f6c5..477927becacb 100644
--- a/Documentation/static-keys.txt
+++ b/Documentation/static-keys.txt
@@ -15,8 +15,8 @@ The updated API replacements are:
DEFINE_STATIC_KEY_TRUE(key);
DEFINE_STATIC_KEY_FALSE(key);
-static_key_likely()
-static_key_unlikely()
+static_branch_likely()
+static_branch_unlikely()
0) Abstract
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 0684bd3a48fc..f1094238ab2a 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -21,8 +21,8 @@
*
* DEFINE_STATIC_KEY_TRUE(key);
* DEFINE_STATIC_KEY_FALSE(key);
- * static_key_likely()
- * static_key_unlikely()
+ * static_branch_likely()
+ * static_branch_unlikely()
*
* Jump labels provide an interface to generate dynamic branches using
* self-modifying code. Assuming toolchain and architecture support, if we
@@ -45,12 +45,10 @@
* statement, setting the key to true requires us to patch in a jump
* to the out-of-line of true branch.
*
- * In addtion to static_branch_{enable,disable}, we can also reference count
+ * In addition to static_branch_{enable,disable}, we can also reference count
* the key or branch direction via static_branch_{inc,dec}. Thus,
* static_branch_inc() can be thought of as a 'make more true' and
- * static_branch_dec() as a 'make more false'. The inc()/dec()
- * interface is meant to be used exclusively from the inc()/dec() for a given
- * key.
+ * static_branch_dec() as a 'make more false'.
*
* Since this relies on modifying code, the branch modifying functions
* must be considered absolute slow paths (machine wide synchronization etc.).