Re: [PATCH v6 1/6] locking/qspinlock: relaxes cmpxchg & xchg ops in native code
From: Waiman Long
Date: Mon Sep 14 2015 - 14:40:32 EST
On 09/14/2015 08:06 AM, Peter Zijlstra wrote:
On Fri, Sep 11, 2015 at 03:27:44PM -0700, Davidlohr Bueso wrote:
On Fri, 11 Sep 2015, Waiman Long wrote:
@@ -46,7 +46,7 @@ static inline bool virt_queued_spin_lock(struct qspinlock *lock)
if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
return false;
- while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0)
+ while (atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) != 0)
cpu_relax();
This code has changed with Peter's recent ccas fix. And the whole virt_queued_spin_lock()
thing will now be under pv configs. So this doesn't apply to native code anymore, so it
looks like it should be dropped altogether.
Yeah, it also doesn't make sense, this ix x86 arch code, x86 cannot do
cmpxchg_acquire. Then again, I suppose we could argue its of
documentation value..
Yes, it is to be consistent with the change in asm_generic qspinlock.h.
We can certainly skip that.
Cheers,
Longman
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/