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locking/rwsem: Set lock ownership ASAP

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In order to optimize the spinning step, we need to set the lock
owner as soon as the lock is acquired; after a successful counter
cmpxchg operation, that is. This is particularly useful as rwsems
need to set the owner to nil for readers, so there is a greater
chance of falling out of the spinning. Currently we only set the
owner much later in the game, in the more generic level -- latency
can be specially bad when waiting for a node->next pointer when
releasing the osq in up_write calls.

As such, update the owner inside rwsem_try_write_lock (when the
lock is obtained after blocking) and rwsem_try_write_lock_unqueued
(when the lock is obtained while spinning). This requires creating
a new internal rwsem.h header to share the owner related calls.

Also cleanup some headers for mutex and rwsem.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jason Low <jason.low2@hp.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/1422609267-15102-4-git-send-email-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Davidlohr Bueso 2015-01-30 01:14:25 -08:00 committed by Ingo Molnar
parent 49e4b2bcf7
commit 7a215f89a0
4 changed files with 28 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
kernel/locking/mutex.c
View File

@ -25,7 +25,7 @@
#include <linux/spinlock.h>
#include <linux/interrupt.h>
#include <linux/debug_locks.h>
#include "mcs_spinlock.h"
#include <linux/osq_lock.h>
/*
* In the DEBUG case we are using the "NULL fastpath" for mutexes,

8
kernel/locking/rwsem-xadd.c
View File

@ -14,8 +14,9 @@
#include <linux/init.h>
#include <linux/export.h>
#include <linux/sched/rt.h>
#include <linux/osq_lock.h>
#include "mcs_spinlock.h"
#include "rwsem.h"
/*
* Guide to the rw_semaphore's count field for common values.
@ -265,6 +266,7 @@ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem)
RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) {
if (!list_is_singular(&sem->wait_list))
rwsem_atomic_update(RWSEM_WAITING_BIAS, sem);
rwsem_set_owner(sem);
return true;
}
@ -284,8 +286,10 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
return false;
old = cmpxchg(&sem->count, count, count + RWSEM_ACTIVE_WRITE_BIAS);
if (old == count)
if (old == count) {
rwsem_set_owner(sem);
return true;
}
count = old;
}

22
kernel/locking/rwsem.c
View File

@ -9,29 +9,9 @@
#include <linux/sched.h>
#include <linux/export.h>
#include <linux/rwsem.h>
#include <linux/atomic.h>
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
static inline void rwsem_set_owner(struct rw_semaphore *sem)
{
sem->owner = current;
}
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
{
sem->owner = NULL;
}
#else
static inline void rwsem_set_owner(struct rw_semaphore *sem)
{
}
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
{
}
#endif
#include "rwsem.h"
/*
* lock for reading

20
kernel/locking/rwsem.h Normal file
View File

@ -0,0 +1,20 @@
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
static inline void rwsem_set_owner(struct rw_semaphore *sem)
{
sem->owner = current;
}
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
{
sem->owner = NULL;
}
#else
static inline void rwsem_set_owner(struct rw_semaphore *sem)
{
}
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
{
}
#endif