Messages in this thread | | | Date | Mon, 14 May 2007 14:07:37 +0200 | From | Nick Piggin <> | Subject | Re: [PATCH 0/2] convert mmap_sem to a scalable rw_mutex |
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On Fri, May 11, 2007 at 07:18:33PM +0200, Peter Zijlstra wrote: > On Fri, 2007-05-11 at 18:52 +0200, Eric Dumazet wrote: > > > > But I personally find this new rw_mutex not scalable at all if you have some > > writers around. > > > > percpu_counter_sum is just a L1 cache eater, and O(NR_CPUS) > > Yeah, that is true; there are two occurences, the one in > rw_mutex_read_unlock() is not strictly needed for correctness. > > Write locks are indeed quite expensive. But given the ratio of > reader:writer locks on mmap_sem (I'm not all that familiar with other > rwsem users) this trade-off seems workable.
I guess the problem with that logic is assuming the mmap_sem read side always needs to be scalable. Given the ratio of threaded:unthreaded apps, maybe the trade-off swings away from favour?
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