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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 4 Sep 2019 17:59:36 +0200
Subject: [PATCH] percpu-refcount: use normal instead of RCU-sched"
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.13-rt7.tar.xz
This is a revert of commit
a4244454df129 ("percpu-refcount: use RCU-sched insted of normal RCU")
which claims the only reason for using RCU-sched is
"rcu_read_[un]lock() … are slightly more expensive than preempt_disable/enable()"
and
"As the RCU critical sections are extremely short, using sched-RCU
shouldn't have any latency implications."
The problem with RCU-sched is that it disables preemption and the
callback must not acquire any sleeping locks like spinlock_t on
PREEMPT_RT which is the case.
Convert back to normal RCU.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/percpu-refcount.h | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
--- a/include/linux/percpu-refcount.h
+++ b/include/linux/percpu-refcount.h
@@ -186,14 +186,14 @@ static inline void percpu_ref_get_many(s
{
unsigned long __percpu *percpu_count;
- rcu_read_lock_sched();
+ rcu_read_lock();
if (__ref_is_percpu(ref, &percpu_count))
this_cpu_add(*percpu_count, nr);
else
atomic_long_add(nr, &ref->count);
- rcu_read_unlock_sched();
+ rcu_read_unlock();
}
/**
@@ -223,7 +223,7 @@ static inline bool percpu_ref_tryget(str
unsigned long __percpu *percpu_count;
bool ret;
- rcu_read_lock_sched();
+ rcu_read_lock();
if (__ref_is_percpu(ref, &percpu_count)) {
this_cpu_inc(*percpu_count);
@@ -232,7 +232,7 @@ static inline bool percpu_ref_tryget(str
ret = atomic_long_inc_not_zero(&ref->count);
}
- rcu_read_unlock_sched();
+ rcu_read_unlock();
return ret;
}
@@ -257,7 +257,7 @@ static inline bool percpu_ref_tryget_liv
unsigned long __percpu *percpu_count;
bool ret = false;
- rcu_read_lock_sched();
+ rcu_read_lock();
if (__ref_is_percpu(ref, &percpu_count)) {
this_cpu_inc(*percpu_count);
@@ -266,7 +266,7 @@ static inline bool percpu_ref_tryget_liv
ret = atomic_long_inc_not_zero(&ref->count);
}
- rcu_read_unlock_sched();
+ rcu_read_unlock();
return ret;
}
@@ -285,14 +285,14 @@ static inline void percpu_ref_put_many(s
{
unsigned long __percpu *percpu_count;
- rcu_read_lock_sched();
+ rcu_read_lock();
if (__ref_is_percpu(ref, &percpu_count))
this_cpu_sub(*percpu_count, nr);
else if (unlikely(atomic_long_sub_and_test(nr, &ref->count)))
ref->release(ref);
- rcu_read_unlock_sched();
+ rcu_read_unlock();
}
/**
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