Messages in this thread | | | Date | Thu, 7 Mar 2019 12:23:44 +0100 | From | Peter Zijlstra <> | Subject | Re: [RFT][Update][PATCH 2/2] cpufreq: intel_pstate: Update max CPU frequency on global turbo changes |
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On Thu, Mar 07, 2019 at 11:02:58AM +0000, Quentin Perret wrote: > Also on recent big little SoCs, the capacity ratio can be pretty high. > You can get little CPUs with 300 of capacity or so. The arbitrary 128 > thing is basically gonna go near max freq in one step, although the CPUs > actually 20 available OPPs or so. And I guess that's a shame.
Ah, but remember; with the latest patch the iowait_boost is scaled on max. So in order to hit that 300, you first have to hit 1024.
+ boost = (sg_cpu->iowait_boost * max) >> SCHED_CAPACITY_SHIFT; + return max(boost, util);
So iowait_boost goes from 128 to 1024 in 4 wakeups (the first sets 128, the next 3 get it to 1024), but the effective value is, given @max == 300:
128 -> 37 256 -> 75 512 -> 150 1024 -> 300
so irrespective of the number of OPPs and their spread, it takes 4 wakeups to get to max.
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