Messages in this thread | | | Date | Sun, 04 Jan 2009 13:22:00 +0100 | From | Manfred Spraul <> | Subject | Re: [RFC, PATCH] kernel/rcu: add kfree_rcu |
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Lai Jiangshan wrote: > I have not posted it. -:) > Could you post it?
Paul: What would break if we stop processing rcu entries in (cpu) order?
The head->func(head) in rcu_do_batch() is probably a nightmare for the branch target predictor.
What about: - shrinking struct rcu_head to just a pointer (let's start with the goodie) - Adding a register_rcu_callback() function. It allocates the per-cpu storage for the rcu grace period lists. Seperate lists for each registered callback - thus no need to copy the callback target into each rcu_head structure. It returns a pointer/handle to these lists. - call_rcu gets that handle instead of the plain function pointer. - rcu_do_batch enumerates all registered callbacks. Thus first all callback_struct->func(head) calls for the first registered callback, then the calls for the 2nd callback, etc. Better for the icache, better for the branch predictor.
Paul: Do you have a test case that is suitable for benchmarking rcu? Any workloads were rcu appears significantly in oprofile? And: Do you know how many rcu entries are typically alive? How much memory is used for the function pointers?
-- Manfred
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