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108 Commits

Author SHA1 Message Date
Jason Low
47667fa150 locking/mutexes: Modify the way optimistic spinners are queued 
The mutex->spin_mlock was introduced in order to ensure that only 1 thread
spins for lock acquisition at a time to reduce cache line contention. When
lock->owner is NULL and the lock->count is still not 1, the spinner(s) will
continually release and obtain the lock->spin_mlock. This can generate
quite a bit of overhead/contention, and also might just delay the spinner
from getting the lock.

This patch modifies the way optimistic spinners are queued by queuing before
entering the optimistic spinning loop as oppose to acquiring before every
call to mutex_spin_on_owner(). So in situations where the spinner requires
a few extra spins before obtaining the lock, then there will only be 1 spinner
trying to get the lock and it will avoid the overhead from unnecessarily
unlocking and locking the spin_mlock.

Signed-off-by: Jason Low <jason.low2@hp.com>
Cc: tglx@linutronix.de
Cc: riel@redhat.com
Cc: akpm@linux-foundation.org
Cc: davidlohr@hp.com
Cc: hpa@zytor.com
Cc: andi@firstfloor.org
Cc: aswin@hp.com
Cc: scott.norton@hp.com
Cc: chegu_vinod@hp.com
Cc: Waiman.Long@hp.com
Cc: paulmck@linux.vnet.ibm.com
Cc: torvalds@linux-foundation.org
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1390936396-3962-3-git-send-email-jason.low2@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2014-03-11 12:14:53 +01:00
Jason Low
46af29e479 locking/mutexes: Return false if task need_resched() in mutex_can_spin_on_owner() 
The mutex_can_spin_on_owner() function should also return false if the
task needs to be rescheduled to avoid entering the MCS queue when it
needs to reschedule.

Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Waiman.Long@hp.com
Cc: torvalds@linux-foundation.org
Cc: tglx@linutronix.de
Cc: riel@redhat.com
Cc: akpm@linux-foundation.org
Cc: davidlohr@hp.com
Cc: hpa@zytor.com
Cc: andi@firstfloor.org
Cc: aswin@hp.com
Cc: scott.norton@hp.com
Cc: chegu_vinod@hp.com
Cc: paulmck@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/1390936396-3962-2-git-send-email-jason.low2@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2014-03-11 12:14:52 +01:00
Peter Zijlstra
c9122da1e2 locking: Move mcs_spinlock.h into kernel/locking/ 
The mcs_spinlock code is not meant (or suitable) as a generic locking
primitive, therefore take it away from the normal includes and place
it in kernel/locking/.

This way the locking primitives implemented there can use it as part
of their implementation but we do not risk it getting used
inapropriately.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-byirmpamgr7h25m5kyavwpzx@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2014-03-11 12:14:52 +01:00
Andi Kleen
22d9fd3411 asmlinkage, mutex: Mark __visible 
Various kernel/mutex.c functions can be called from
inline assembler, so they should be all global and
__visible.

Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/1391845930-28580-7-git-send-email-ak@linux.intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
 2014-02-13 18:13:19 -08:00
Tim Chen
e72246748f locking/mutexes/mcs: Restructure the MCS lock defines and locking code into its own file 
We will need the MCS lock code for doing optimistic spinning for rwsem
and queued rwlock.  Extracting the MCS code from mutex.c and put into
its own file allow us to reuse this code easily.

We also inline mcs_spin_lock and mcs_spin_unlock functions
for better efficiency.

Note that using the smp_load_acquire/smp_store_release pair used in
mcs_lock and mcs_unlock is not sufficient to form a full memory barrier
across cpus for many architectures (except x86).  For applications that
absolutely need a full barrier across multiple cpus with mcs_unlock and
mcs_lock pair, smp_mb__after_unlock_lock() should be used after mcs_lock.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1390347360.3138.63.camel@schen9-DESK
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2014-01-28 13:13:27 +01:00
Waiman Long
aff7385b5a locking/mutexes/mcs: Correct barrier usage 
This patch corrects the way memory barriers are used in the MCS lock
with smp_load_acquire and smp_store_release fucnctions.  The previous
barriers could leak critical sections if mcs lock is used by itself.
It is not a problem when mcs lock is embedded in mutex but will be an
issue when the mcs_lock is used elsewhere.

The patch removes the incorrect barriers and put in correct
barriers with the pair of functions smp_load_acquire and smp_store_release.

Suggested-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1390347353.3138.62.camel@schen9-DESK
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2014-01-28 13:13:26 +01:00
Peter Zijlstra
67a6de49bf locking/doc: Update references to kernel/mutex.c 
Fix this docbook error:

  >> docproc: kernel/mutex.c: No such file or directory

by updating the stale references to kernel/mutex.c.

Reported-by: fengguang.wu@intel.com
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-34pikw1tlsskj65rrt5iusrq@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2013-11-11 12:41:33 +01:00
Peter Zijlstra
01768b42dc locking: Move the mutex code to kernel/locking/ 
Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-1ditvncg30dgbpvrz2bxfmke@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 2013-11-06 07:55:07 +01:00