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locking/qspinlock/x86: Fix performance regression under unaccelerated VMs

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commit 43b3f02899 upstream.

Dave ran into horrible performance on a VM without PARAVIRT_SPINLOCKS
set and Linus noted that the test-and-set implementation was retarded.

One should spin on the variable with a load, not a RMW.

While there, remove 'queued' from the name, as the lock isn't queued
at all, but a simple test-and-set.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Dave Chinner <david@fromorbit.com>
Tested-by: Dave Chinner <david@fromorbit.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Waiman Long <Waiman.Long@hp.com>
Link: http://lkml.kernel.org/r/20150904152523.GR18673@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peter Zijlstra
2015-09-04 17:25:23 +02:00
committed by Greg Kroah-Hartman
parent d78a2be4f9
commit 304b8b47da
3 changed files with 15 additions and 7 deletions
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2
kernel/locking/qspinlock.c
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@@ -289,7 +289,7 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
if (pv_enabled())
goto queue;
if (virt_queued_spin_lock(lock))
if (virt_spin_lock(lock))
return;
/*