Messages in this thread | | | Subject | Re: [patch]x86: spread tlb flush vector between nodes | From | Shaohua Li <> | Date | Tue, 19 Oct 2010 13:39:17 +0800 |
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On Wed, 2010-10-13 at 16:39 +0800, Shaohua Li wrote: > On Wed, 2010-10-13 at 16:16 +0800, Andi Kleen wrote: > > On Wed, Oct 13, 2010 at 03:41:38PM +0800, Shaohua Li wrote: > > > > Hi Shaohua, > > > > > Currently flush tlb vector allocation is based on below equation: > > > sender = smp_processor_id() % 8 > > > This isn't optimal, CPUs from different node can have the same vector, this > > > causes a lot of lock contention. Instead, we can assign the same vectors to > > > CPUs from the same node, while different node has different vectors. This has > > > below advantages: > > > a. if there is lock contention, the lock contention is between CPUs from one > > > node. This should be much cheaper than the contention between nodes. > > > b. completely avoid lock contention between nodes. This especially benefits > > > kswapd, which is the biggest user of tlb flush, since kswapd sets its affinity > > > to specific node. > > > > The original scheme with 8 vectors was designed when Linux didn't have > > per CPU interrupt numbers yet, and interrupts vectors were a scarce resource. > > > > Now that we have per CPU interrupts and there is no immediate danger > > of running out I think it's better to use more than 8 vectors for the TLB > > flushes. > > > > Perhaps could use 32 vectors or so and give each node on a 8S > > system 4 slots and on a 4 node system 8 slots? > Haven't too much idea. Before we have per CPU interrupts, muti vector > msi-x isn't widely deployed. Thought we need data if this is really > required. looks there are still some overhead with total 8 vectors in a big machine. I'll try the 32 vectors as you suggested. I'll send separate patches out to address the 32 vectors issue. Can we merge this patch first?
Thanks, Shaohua
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