cpufreq: AMD "frequency sensitivity feedback" powersave bias for ondemand governor

Future AMD processors, starting with Family 16h, can provide software
with feedback on how the workload may respond to frequency change --
memory-bound workloads will not benefit from higher frequency, where
as compute-bound workloads will. This patch enables this "frequency
sensitivity feedback" to aid the ondemand governor to make better
frequency change decisions by hooking into the powersave bias.

Signed-off-by: Jacob Shin <jacob.shin@amd.com>
Acked-by: Thomas Renninger <trenn@suse.de>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt
index 4dfed30b7fda..66f9cc310686 100644
--- a/Documentation/cpu-freq/governors.txt
+++ b/Documentation/cpu-freq/governors.txt
@@ -167,6 +167,27 @@ of load evaluation and helping the CPU stay at its top speed when truly
 busy, rather than shifting back and forth in speed. This tunable has no
 effect on behavior at lower speeds/lower CPU loads.
 
+powersave_bias: this parameter takes a value between 0 to 1000. It
+defines the percentage (times 10) value of the target frequency that
+will be shaved off of the target. For example, when set to 100 -- 10%,
+when ondemand governor would have targeted 1000 MHz, it will target
+1000 MHz - (10% of 1000 MHz) = 900 MHz instead. This is set to 0
+(disabled) by default.
+When AMD frequency sensitivity powersave bias driver --
+drivers/cpufreq/amd_freq_sensitivity.c is loaded, this parameter
+defines the workload frequency sensitivity threshold in which a lower
+frequency is chosen instead of ondemand governor's original target.
+The frequency sensitivity is a hardware reported (on AMD Family 16h
+Processors and above) value between 0 to 100% that tells software how
+the performance of the workload running on a CPU will change when
+frequency changes. A workload with sensitivity of 0% (memory/IO-bound)
+will not perform any better on higher core frequency, whereas a
+workload with sensitivity of 100% (CPU-bound) will perform better
+higher the frequency. When the driver is loaded, this is set to 400
+by default -- for CPUs running workloads with sensitivity value below
+40%, a lower frequency is chosen. Unloading the driver or writing 0
+will disable this feature.
+
 
 2.5 Conservative
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