Date: Thu, 12 Nov 2015 13:35:21 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: ralf@linux-mips.org, ddaney@caviumnetworks.com
Cc: linux-kernel@vger.kernel.org, Paul McKenney <paulmck@linux.vnet.ibm.com>,
        Will Deacon <will.deacon@arm.com>, torvalds@linux-foundation.org,
        boqun.feng@gmail.com
Subject: Re: [RFC][PATCH] mips: Fix arch_spin_unlock()
Message-ID: <20151112123521.GJ11639@twins.programming.kicks-ass.net>
References: <20151112123123.GZ17308@twins.programming.kicks-ass.net>
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On Thu, Nov 12, 2015 at 01:31:23PM +0100, Peter Zijlstra wrote:
> +++ b/arch/mips/include/asm/spinlock.h
> @@ -140,7 +140,7 @@ static inline void arch_spin_lock(arch_spinlock_t *lock)
>  static inline void arch_spin_unlock(arch_spinlock_t *lock)
>  {
>  	unsigned int serving_now = lock->h.serving_now + 1;
> -	wmb();
> +	smp_mb();
>  	lock->h.serving_now = (u16)serving_now;

Also, you might want to consider using WRITE_ONCE() for that store.

>  	nudge_writes();

And that thing is creative, I've not seen any other arch issues barriers
to speed up the store buffer flush. Does it really matter for MIPS?

>  }
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