On 1/24/20 2:52 AM, Peter Zijlstra wrote: > On Thu, Jan 23, 2020 at 04:33:54PM -0500, Alex Kogan wrote: >> Let me put this question to you. What do you think the number should be? > I think it would be very good to keep the inter-node latency below 1ms. It is hard to guarantee that given that lock hold times can vary quite a lot depending on the workload. What we can control is just how many later lock waiters can jump ahead before a given waiter. > But to realize that we need data on the lock hold times. Specifically > for the heavily contended locks that make CNA worth it in the first > place. > > I don't see that data, so I don't see how we can argue about this let > alone call something reasonable. > In essence, CNA lock is for improving throughput on NUMA machines at the expense of increasing worst case latency. If low latency is important, it should be disabled. If CONFIG_PREEMPT_RT is on, CONFIG_NUMA_AWARE_SPINLOCKS should be off. Cheers, Longman
