Messages in this thread | | | Date | Fri, 19 Nov 2004 18:34:43 -0800 | From | William Lee Irwin III <> | Subject | Re: page fault scalability patch V11 [0/7]: overview |
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William Lee Irwin III wrote: >> Split counters easily resolve the issues with both these approaches >> (and apparently your co-workers are suggesting it too, and have >> performance results backing it).
On Sat, Nov 20, 2004 at 01:18:22PM +1100, Nick Piggin wrote: > Split counters still require atomic operations though. This is what > Christoph's latest effort is directed at removing. And they'll still > bounce cachelines around. (I assume we've reached the conclusion > that per-cpu split counters per-mm won't fly?).
Split != per-cpu, though it may be. Counterexamples are as simple as atomic_inc(&mm->rss[smp_processor_id()>>RSS_IDX_SHIFT]); Furthermore, see Robin Holt's results regarding the performance of the atomic operations and their relation to cacheline sharing.
And frankly, the argument that the space overhead of per-cpu counters is problematic is not compelling. Even at 1024 cpus it's smaller than an ia64 pagetable page, of which there are numerous instances attached to each mm.
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