Nick Piggin wrote:
And either way, spinlocks are still much more costly than rwlocks, because they still have that first exclusive request, who's effectiveness deteriorates under load. That you *also* have these follow on shared accesses (which will need to be invalidated somehow later anyway), doesn't make them better than read locks.
I shouldn't say much more costly.... Much more costly when looking at the limit case (and we traditionally rather look at the common case in Linux, and in those cases spinlocks _can_ be faster). However in the limit, spinlocks scale O(N), while readlocks scale O(1), where N is the number of CPUs trying to take the lock. AFAIKS. But if they're causing stability problems, I have no arguments against converting them to spinlocks. It might even result in a worldwide net saving of CPU cycles, for what that's worth ;) -- SUSE Labs, Novell Inc.Send instant messages to your online friends http://au.messenger.yahoo.com -
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- Re: [patch] increase spinlock-debug looping timeouts (write_lock and NMI)
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