Commit 93edc8bd authored Sep 11, 2015 by Waiman Long Committed by Ingo Molnar Sep 18, 2015

locking/pvqspinlock: Kick the PV CPU unconditionally when _Q_SLOW_VAL



If _Q_SLOW_VAL has been set, the vCPU state must have been vcpu_hashed.
The extra check at the end of __pv_queued_spin_unlock() is unnecessary
and can be removed.

Signed-off-by: Waiman Long <Waiman.Long@hpe.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Douglas Hatch <doug.hatch@hp.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1441996658-62854-3-git-send-email-Waiman.Long@hpe.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent c55a6ffa

kernel/locking/qspinlock_paravirt.h

+1 −5

Original line number	Diff line number	Diff line
		@@ -267,7 +267,6 @@ static void pv_wait_head(struct qspinlock lock, struct mcs_spinlock node)
		}

		if (!lp) { /* ONCE */
		WRITE_ONCE(pn->state, vcpu_hashed);
		lp = pv_hash(lock, pn);

		/*
		@@ -275,11 +274,9 @@ static void pv_wait_head(struct qspinlock lock, struct mcs_spinlock node)
		* when we observe _Q_SLOW_VAL in __pv_queued_spin_unlock()
		* we'll be sure to be able to observe our hash entry.
		*
		* [S] pn->state
		* [S] <hash> [Rmw] l->locked == _Q_SLOW_VAL
		* MB RMB
		* [RmW] l->locked = _Q_SLOW_VAL [L] <unhash>
		* [L] pn->state
		*
		* Matches the smp_rmb() in __pv_queued_spin_unlock().
		*/
		@@ -364,7 +361,6 @@ __visible void __pv_queued_spin_unlock(struct qspinlock *lock)
		* vCPU is harmless other than the additional latency in completing
		* the unlock.
		*/
		if (READ_ONCE(node->state) == vcpu_hashed)
		pv_kick(node->cpu);
		}
		/*