Messages in this thread | | | Date | Mon, 17 Jul 2017 11:21:11 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFC PATCH v1 00/11] Create fast idle path for short idle periods |
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On Fri, Jul 14, 2017 at 09:03:14AM -0700, Andi Kleen wrote: > fast idle doesn't have an upper bound. > > If the prediction exceeds the fast idle threshold any C state can be used. > > It's just another state (fast C1), but right now it has an own threshold > which may be different from standard C1.
Given it uses the same estimate we end up with:
select_c_state(idle_est) { if (idle_est < fast_threshold) return C1;
if (idle_est < C1_threshold) return C1; if (idle_est < C2_threshold) return C2; /* ... */
return C6 }
Now, unless you're mister Turnbull, C2 will never get selected when fast_threshold > C2_threshold.
Which is wrong. If you want to effectively scale the selection of C1, why not also change the C2 and further criteria.
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