On Mon, Nov 21, 2016 at 01:53:08PM +0000, Juri Lelli wrote:
On 21/11/16 13:26, Peter Zijlstra wrote:
So the limited decay would be the dominant factor in ramp-up time, leaving the regular PELT period the dominant factor for ramp-down.
Hmmm, AFAIU the limited decay will help not forgetting completely the contribution of tasks that sleep for a long time, but it won't modify the actual ramp-up of the signal. So, for new tasks we will need to play with a sensible initial value (trading off perf and power as usual).
Oh, you mean ramp-up for bright spanking new tasks? I forgot the details, but I think we can fudge the 'history' such that those too ramp up quickly.
(Note that the decay limit would only be applied on the per-task signal, not the accumulated signal.)
Right, and since schedutil consumes the latter, we could still suffer from too frequent frequency switch events I guess (this is where the down threshold thing came as a quick and dirty fix). Maybe we can think of some smoothing applied to the accumulated signal, or make it decay slower (don't really know what this means in practice, though :) ?
Not sure I follow. So by limiting decay to the task value, the moment we add it back to the accumulated signal (wakeup), the accumulated signal jumps up quickly and ramp-up is achieved.