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Message-ID: <20140102091915.GC1757@opentech.at>
Date: Thu, 2 Jan 2014 10:19:15 +0100
From: Nicholas Mc Guire <der.herr@...r.at>
To: linux-rt-users@...r.kernel.org
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
Carsten Emde <C.Emde@...dl.org>,
Thomas Gleixner <tglx@...utronix.de>,
Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH RT 2/2] read_lock migrate_disable pushdown to rt_read_lock
pushdown of migrate_disable/enable from read_*lock* to the rt_read_*lock*
api level
general mapping to mutexes:
read_*lock*
`-> rt_read_*lock*
`-> __spin_lock (the sleeping spin locks)
`-> rt_mutex
The real read_lock* mapping:
read_lock_irqsave -.
read_lock_irq `-> rt_read_lock_irqsave()
`->read_lock ---------. \
read_lock_bh ------+ \
`--> rt_read_lock()
if (rt_mutex_owner(lock) != current){
`-> __rt_spin_lock()
rt_spin_lock_fastlock()
`->rt_mutex_cmpxchg()
migrate_disable()
}
rwlock->read_depth++;
read_trylock mapping:
read_trylock
`-> rt_read_trylock
if (rt_mutex_owner(lock) != current){
`-> rt_mutex_trylock()
rt_mutex_fasttrylock()
rt_mutex_cmpxchg()
migrate_disable()
}
rwlock->read_depth++;
read_unlock* mapping:
read_unlock_bh --------+
read_unlock_irq -------+
read_unlock_irqrestore +
read_unlock -----------+
`-> rt_read_unlock()
if(--rwlock->read_depth==0){
`-> __rt_spin_unlock()
rt_spin_lock_fastunlock()
`-> rt_mutex_cmpxchg()
migrate_disable()
}
So calls to migrate_disable/enable() are better placed at the rt_read_*
level of lock/trylock/unlock as all of the read_*lock* API has this as a
common path. In the rt_read* API of lock/trylock/unlock the nesting level
is already being recorded in rwlock->read_depth, so we can push down the
migrate disable/enable to that level and condition it on the read_depth
going from 0 to 1 -> migrate_disable and 1 to 0 -> migrate_enable. This
eliminates the recursive calls that were needed when migrate_disable/enable
was done at the read_*lock* level.
The approach to read_*_bh also eliminates the concerns raised with the
regards to api inbalances (read_lock_bh -> read_unlock+local_bh_enable)
this is on top of 3.12.6-rt9 with
timers-do-not-raise-softirq-unconditionally.patch removed
No change of functional behavior
Tested-by: Carsten Emde <C.Emde@...dl.org>
Signed-off-by: Nicholas Mc Guire <der.herr@...r.at>
---
include/linux/rwlock_rt.h | 6 ------
kernel/rt.c | 9 +++++----
2 files changed, 5 insertions(+), 10 deletions(-)
diff --git a/include/linux/rwlock_rt.h b/include/linux/rwlock_rt.h
index a276fae..e85a5df 100644
--- a/include/linux/rwlock_rt.h
+++ b/include/linux/rwlock_rt.h
@@ -33,7 +33,6 @@ extern void __rt_rwlock_init(rwlock_t *rwlock, char *name, struct lock_class_key
#define read_lock_irqsave(lock, flags) \
do { \
typecheck(unsigned long, flags); \
- migrate_disable(); \
flags = rt_read_lock_irqsave(lock); \
} while (0)
@@ -45,14 +44,12 @@ extern void __rt_rwlock_init(rwlock_t *rwlock, char *name, struct lock_class_key
#define read_lock(lock) \
do { \
- migrate_disable(); \
rt_read_lock(lock); \
} while (0)
#define read_lock_bh(lock) \
do { \
local_bh_disable(); \
- migrate_disable(); \
rt_read_lock(lock); \
} while (0)
@@ -74,13 +71,11 @@ extern void __rt_rwlock_init(rwlock_t *rwlock, char *name, struct lock_class_key
#define read_unlock(lock) \
do { \
rt_read_unlock(lock); \
- migrate_enable(); \
} while (0)
#define read_unlock_bh(lock) \
do { \
rt_read_unlock(lock); \
- migrate_enable(); \
local_bh_enable(); \
} while (0)
@@ -104,7 +99,6 @@ extern void __rt_rwlock_init(rwlock_t *rwlock, char *name, struct lock_class_key
typecheck(unsigned long, flags); \
(void) flags; \
rt_read_unlock(lock); \
- migrate_enable(); \
} while (0)
#define write_unlock_irqrestore(lock, flags) \
diff --git a/kernel/rt.c b/kernel/rt.c
index c43c923..5d17727 100644
--- a/kernel/rt.c
+++ b/kernel/rt.c
@@ -211,19 +211,18 @@ int __lockfunc rt_read_trylock(rwlock_t *rwlock)
* but not when read_depth == 0 which means that the lock is
* write locked.
*/
- migrate_disable();
if (rt_mutex_owner(lock) != current) {
ret = rt_mutex_trylock(lock);
- if (ret)
+ if (ret) {
rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_);
+ migrate_disable();
+ }
} else if (!rwlock->read_depth) {
ret = 0;
}
if (ret)
rwlock->read_depth++;
- else
- migrate_enable();
return ret;
}
@@ -247,6 +246,7 @@ void __lockfunc rt_read_lock(rwlock_t *rwlock)
if (rt_mutex_owner(lock) != current) {
rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_);
__rt_spin_lock(lock);
+ migrate_disable();
}
rwlock->read_depth++;
}
@@ -268,6 +268,7 @@ void __lockfunc rt_read_unlock(rwlock_t *rwlock)
if (--rwlock->read_depth == 0) {
rwlock_release(&rwlock->dep_map, 1, _RET_IP_);
__rt_spin_unlock(&rwlock->lock);
+ migrate_enable();
}
}
EXPORT_SYMBOL(rt_read_unlock);
--
1.7.2.5
--
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