On Fri, 2018-02-02 at 19:48 +0000, Mel Gorman wrote: > On Fri, Feb 02, 2018 at 06:54:24AM -0800, Srinivas Pandruvada wrote: > > > > > No idea, desired would be the one I would start with, it > > > > > matches > > > > > with > > > > > the intent here. But I've no idea what our current HWP > > > > > implementation > > > > > actually does with it. > > > > > > > > Desired !=0 will disable HWP autonomous mode of frequency > > > > selection. > > > > > > But I don't think it will just run at "desired" then, will it? > > > > HWP all are these hints only not a guarantee. > > Sure, but the lack on detection when tasks are low utilisation but > still > latency/throughput sensitive is problematic. Users shouldn't have to > know they need to disable HWP or set performance goernor out of the > box. > It's only going to get worse as sockets get larger. I am not saying that we shouldn't do anything. Can you give me some workloads which you care the most?
> > > There are totally different way HWP is handled in client an > > servers. > > If you set desired all heuristics they collected will be dumped, so > > they suggest don't set desired when you are in autonomous mode. If > > we > > really want a boost set the EPP. We know that EPP makes lots of > > measurable difference. > > > > Sure boosting EPP makes a difference -- it's essentially what the > performance > goveror does and I know that can be done by a user but it's still > basically a > cop-out. Default performance for low utilisation or lightly loaded > machines > is poor. Maybe it should be set based on the ACPI preferred profile > but > that information is not always available. It would be nice if *some* > sort of hint about new migrations or tasks waking from IO would be > desirable. EPP is a range not a single value. So you don't need to make EPP=0 as a performance governor. PeterZ gave me some scheduler change to experiment, which can be used as hint to play with EPP. Thanks, Srinivas