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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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6393d6a102
Currently, ondemand calculates the target frequency proportional to load using the formula: Target frequency = C * load where C = policy->cpuinfo.max_freq / 100 Though, in many cases, the minimum available frequency is pretty high and the above calculation introduces a dead band from load 0 to 100 * policy->cpuinfo.min_freq / policy->cpuinfo.max_freq where the target frequency is always calculated to less than policy->cpuinfo.min_freq and the minimum frequency is selected. For example: on Intel i7-3770 @ 3.4GHz the policy->cpuinfo.min_freq = 1600000 and the policy->cpuinfo.max_freq = 3400000 (without turbo). Thus, the CPU starts to scale up at a load above 47. On quad core 1500MHz Krait the policy->cpuinfo.min_freq = 384000 and the policy->cpuinfo.max_freq = 1512000. Thus, the CPU starts to scale at load above 25. Change the calculation of target frequency to eliminate the above effect using the formula: Target frequency = A + B * load where A = policy->cpuinfo.min_freq and B = (policy->cpuinfo.max_freq - policy->cpuinfo->min_freq) / 100 This will map load values 0 to 100 linearly to cpuinfo.min_freq to cpuinfo.max_freq. Also, use the CPUFREQ_RELATION_C in __cpufreq_driver_target to select the closest frequency in frequency_table. This is necessary to avoid selection of minimum frequency only when load equals to 0. It will also help for selection of frequencies using a more 'fair' criterion. Tables below show the difference in selected frequency for specific values of load without and with this patch. On Intel i7-3770 @ 3.40GHz: Without With Load Target Selected Target Selected 0 0 1600000 1600000 1600000 5 170050 1600000 1690050 1700000 10 340100 1600000 1780100 1700000 15 510150 1600000 1870150 1900000 20 680200 1600000 1960200 2000000 25 850250 1600000 2050250 2100000 30 1020300 1600000 2140300 2100000 35 1190350 1600000 2230350 2200000 40 1360400 1600000 2320400 2400000 45 1530450 1600000 2410450 2400000 50 1700500 1900000 2500500 2500000 55 1870550 1900000 2590550 2600000 60 2040600 2100000 2680600 2600000 65 2210650 2400000 2770650 2800000 70 2380700 2400000 2860700 2800000 75 2550750 2600000 2950750 3000000 80 2720800 2800000 3040800 3000000 85 2890850 |
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