Messages in this thread | | | Date | Thu, 29 Mar 2007 15:16:49 -0700 (PDT) | From | Davide Libenzi <> | Subject | Re: [patch] queued spinlocks (i386) |
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On Thu, 29 Mar 2007, Oleg Nesterov wrote:
> 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,
Why? Is CONFIG_PREEMPT friendly to anyone? :)
> > + 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?
Yes, preemption and deterministic spinlock policies are not friends.
- Davide
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