>enable_irq/disable_irq are quite expensive and should not be used
disable_irq is expensive but disable_irq_nosync is quite fast as it
complete even if there are other irq running at the same time.
>are better off disabling interrupts directly on the device (most sane
>hardware has a bit to disable it) or using spin locks.
If you need to grab the spinlock for a rasonable time then the best is to
disable_irq_nosync and then grab the spinlock as 3c509 does, so you won't
harm irq latency and you'll scale equally well as a local cli on SMP.
Andrea
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