Re: [patch] queued spinlocks (i386)
From: Oleg Nesterov
Date: Thu Mar 29 2007 - 14:43:04 EST
On 03/28, Nick Piggin wrote:
>
> Well with my queued spinlocks, all that lockbreak stuff can just come out
> of the spin_lock, break_lock out of the spinlock structure, and
> need_lockbreak just becomes (lock->qhead - lock->qtail > 1).
Q: queued spinlocks are not CONFIG_PREEMPT friendly,
> + asm volatile(LOCK_PREFIX "xaddw %0, %1\n\t"
> + : "+r" (pos), "+m" (lock->qhead) : : "memory");
> + while (unlikely(pos != lock->qtail))
> + cpu_relax();
once we incremented lock->qhead, we have no optiion but should spin with
preemption disabled until pos == lock->qtail, yes?
Oleg.
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