On Thu, Jul 13, 2017 at 10:48:55PM +0800, Li, Aubrey wrote: > - totally from arch_cpu_idle_enter entry to arch_cpu_idle_exit return costs > 9122ns - 15318ns. > ---- In this period(arch idle), rcu_idle_enter costs 1985ns - 2262ns, > rcu_idle_exit > costs 1813ns - 3507ns > > Besides RCU,
So Paul wants more details on where RCU hurts so we can try to fix. > the period includes c-state selection on X86, a few timestamp updates > and a few computations in menu governor. Also, deep HW-cstate latency can be > up > to 100+ microseconds, even if the system is very busy, CPU still has chance > to enter > deep cstate, which I guess some outburst workloads are not happy with it. > > That's my major concern without a fast idle path. Fixing C-state selection by creating an alternative idle path sounds so very wrong.
