On Wed, Nov 15, 2017 at 04:43:32PM +0800, Wanpeng Li wrote: > Hi Peterz, > > I found big performance difference as I discuss with you several days ago. > > ebizzy -M > vanilla static/local cpumask per-cpu cpumask > 8 vCPUs 10152 10083 10117 > 16 vCPUs 1224 4866 10008 > 24 vCPUs 1109 3871 9928 > 32 vCPUs 1025 3375 9811 > > In addition, I can observe ~50% perf top time is occupied by > smp_call_function_many(), ~30% perf top time is occupied by > call_function_interrupt() in the guest when running ebizzy for > static/local cpumask variable. However, I almost can't observe these > IPI stuffs after changing to per-cpu variable. Any opinions?
That doesn't really make sense.. :/ So a single static variable is broken (multiple CPUs can call flush_tlb_others() concurrently and overwrite each others masks). But I don't see why a per-cpu variable would be much slower than an on-stack variable.
