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Martin Bligh (on Thu, 24 Aug 2006 08:53:39 -0700) wrote: >Andrew Morton wrote: >> On Thu, 24 Aug 2006 13:10:09 +1000 >> Nick Piggin <nickpiggin@yahoo.com.au> wrote: >> >> >>>Edward Falk wrote: >>> >>>>Add spin_lock_string_flags and _raw_spin_lock_flags() to >>>>asm-x86_64/spinlock.h so that _spin_lock_irqsave() has the same >>>>semantics on x86_64 as it does on i386 and does *not* have interrupts >>>>disabled while it is waiting for the lock. >>>> >>>>This fix is courtesy of Michael Davidson >>> >>>So, what's the bug? You shouldn't rely on these semantics anyway >>>because you should never expect to wait for a spinlock for so long >>>(and it may be the case that irqs can't be enabled anyway). AFAICT the first architecture that enabled interrupts while spinning was IA64. http://www.gelato.unsw.edu.au/archives/linux-ia64/0404/9161.html I did that patch because large NUMA systems were suffering from cache line bouncing on spinlocks which increased the time that interrupts were disabled. This effect tends not to show up on small systems, but it does make a measurable difference for large systems. An additional benefit of enabling interrupts in the contention path is that it lets you get in with a profiler or debugger to track down deadlock or long lock problems. Enabling interrupts in the contention path has no disadvantages and it increases system responsiveness and availability. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||||
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