Bill.Holler wrote: > Hi Aubrey, > > Time based sample periods were initially investigated, but they > performed poorly with "ping pong" type workloads such as > producer consumer etc. The problem was it took too long to > recognize a load change when the CPU had very short idle > and load periods. The current idle-rate based sampling shows > very little to no regression on benchmarks such as libmicro. > > How does the proposed change look in libmicro? > > We may need to use a hybrid governor which looks at both > idle rate and a fixed sample period. > > Thank you, > Bill
The initial ladder governor we used should have the good performance with "ping pong" type workload but poor perf/power tradeoff. If the sample period is too short, we can't avoid transient flick so that we have C1 residency when idle, not in C3, and especially, the package c-state residency is poor. And if the sample period is too long, we may have bad latency issue with "ping pong" workload. So a good tradeoff is desired, the suggested interval in patch is a good value for SPECpower. I'll send libmicro result to you next week. A hybrid governor may be better, depends on how we implement it, :) Thanks, -Aubrey
