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Date: Wed, 30 Jul 2014 13:41:51 -0700 From: Davidlohr Bueso <davidlohr@...com> To: peterz@...radead.org, mingo@...nel.org Cc: jason.low2@...com, davidlohr@...com, aswin@...com, linux-kernel@...r.kernel.org Subject: [PATCH -tip v2 2/7] locking/mutex: Document quick lock release when unlocking When unlocking, we always want to reach the slowpath with the lock's counter indicating it is unlocked. -- as returned by the asm fastpath call or by explicitly setting it. While doing so, at least in theory, we can optimize and allow faster lock stealing. When unlocking, we always want to reach the slowpath with the lock's counter indicating it is unlocked. -- as returned by the asm fastpath call or by explicitly setting it. While doing so, at least in theory, we can optimize and allow faster lock stealing. Signed-off-by: Davidlohr Bueso <davidlohr@...com> --- Changes from v1: - Moved comment about value of the counter below to make sense only if the fastpath leaves the counter unlocked. kernel/locking/mutex.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index ad0e333..93bec48 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -684,9 +684,16 @@ __mutex_unlock_common_slowpath(struct mutex *lock, int nested) unsigned long flags; /* - * some architectures leave the lock unlocked in the fastpath failure + * As a performance measurement, release the lock before doing other + * wakeup related duties to follow. This allows other tasks to acquire + * the lock sooner, while still handling cleanups in past unlock calls. + * This can be done as we do not enforce strict equivalence between the + * mutex counter and wait_list. + * + * + * Some architectures leave the lock unlocked in the fastpath failure * case, others need to leave it locked. In the later case we have to - * unlock it here + * unlock it here - as the lock counter is currently 0 or negative. */ if (__mutex_slowpath_needs_to_unlock()) atomic_set(&lock->count, 1); -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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