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locking/qspinlock: Use __this_cpu_dec() instead of full-blown this_cpu_dec()

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queued_spin_lock_slowpath() should not worry about another
queued_spin_lock_slowpath() running in interrupt context and
changing node->count by accident, because node->count keeps
the same value every time we enter/leave queued_spin_lock_slowpath().

On some architectures this_cpu_dec() will save/restore irq flags,
which has high overhead. Use the much cheaper __this_cpu_dec() instead.

Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman.Long@hpe.com
Link: http://lkml.kernel.org/r/1465886247-3773-1-git-send-email-xinhui.pan@linux.vnet.ibm.com
[ Rewrote changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Pan Xinhui 2016-06-14 14:37:27 +08:00 committed by Ingo Molnar
parent ebff09a6ff
commit 0dceeaf599
1 changed files with 1 additions and 1 deletions
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2
kernel/locking/qspinlock.c
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@ -619,7 +619,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
/*
* release the node
*/
this_cpu_dec(mcs_nodes[0].count);
__this_cpu_dec(mcs_nodes[0].count);
}
EXPORT_SYMBOL(queued_spin_lock_slowpath);