Eric Saxe wrote: > David Vengerov wrote: > >> Eric Saxe wrote: >> >>> For a default, I was leaning towards "maximize performance, but >>> don't squander power". That way, without doing anything system >>> administrators / users will still get the performance levels they >>> have come to expect..but will also see overall efficiency >>> improvements, since average system utilization is generally very low. >> >> >> So if the system has 8 CPUs and 8 threads running, how do you decide >> on the number of CPUs to keep idle and clocked down? Maybe 8 threads >> on a single CPU will still be satisfactory from the application's >> point of view? > > I think we would always want threads to run on (even a clocked down > CPU) rather than not run at all (waiting on a run queue somewhere). If > the policy is to maximize performance without squandering power, then > with 8 threads and 8 logical CPUs, I would probably say none of the > CPUs should be clocked down, since we would be at 100% utilization.
OK, but what do you then mean by "not squandering power" if N or more threads are present in an N-CPU system? Would it be something like running CPUs at 75% of maximum frequency if there are N threads in an N-CPU system, at 90% if there are 2N threads and 100% if there are more than 3N threads? What is a sample scenario when you would like the system to "coalesce" the workload? David
