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Intel P-State offers two interface to set performance limits: - Intel P-State sysfs /sys/devices/system/cpu/intel_pstate/max_perf_pct /sys/devices/system/cpu/intel_pstate/min_perf_pct - cpufreq /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq /sys/devices/system/cpu/cpu*/cpufreq/scaling_min_freq In the current implementation both of the above methods, change limits to every CPU in the system. Moreover the limits placed using cpufreq policy interface also presented in the Intel P-State sysfs via modified max_perf_pct and min_per_pct during sysfs reads. This allows to check percent of reduced/increased performance, irrespective of method used to limit. There are some new generations of processors, where it is possible to have limits placed on individual CPU cores. Using cpufreq interface it is possible to set limits on each CPU. But the current processing will use last limits placed on all CPUs. So the per core limit feature of CPUs can't be used. This change brings in capability to set P-States limits for each CPU, with some limitations. In this case what should be the read of max_perf_pct and min_perf_pct? It can be most restrictive limits placed on any CPU or max possible performance on any given CPU on which no limits are placed. In either case someone will have issue. So the consensus is, we can't have both sysfs controls present when user wants to use limit per core limits. - By default per-core-control feature is not enabled. So no one will notice any difference. - The way to enable is by kernel command line intel_pstate=per_cpu_perf_limits - When the per-core-controls are enabled there is no display of for both read and write on /sys/devices/system/cpu/intel_pstate/max_perf_pct /sys/devices/system/cpu/intel_pstate/min_perf_pct - User can change limits using /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq /sys/devices/system/cpu/cpu*/cpufreq/scaling_min_freq /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor - User can still observe turbo percent and number of P-States from /sys/devices/system/cpu/intel_pstate/turbo_pct /sys/devices/system/cpu/intel_pstate/num_pstates - User can read write system wide turbo status /sys/devices/system/cpu/no_turbo While changing this BUG_ON is changed to WARN_ON, as they are not fatal errors for the system. Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> |
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