path: root/Documentation/cpu-freq
diff options
authorSrinivas Pandruvada <>2016-10-25 13:20:42 -0700
committerRafael J. Wysocki <>2016-11-01 06:04:06 +0100
commit9e472f95e480d6746ed8646634e6b11994207015 (patch)
treefbaa91caf6fef524d3f6a181581870bd6b20acd1 /Documentation/cpu-freq
parent5879f877398a2a5e5006c6e16a4288e9d4c308a1 (diff)
Documentation: intel_pstate: Update per core limits
Document restriction on per core P-State control. Signed-off-by: Srinivas Pandruvada <> Signed-off-by: Rafael J. Wysocki <>
Diffstat (limited to 'Documentation/cpu-freq')
1 files changed, 20 insertions, 1 deletions
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
index 5528d6d59687..198b2ef88aec 100644
--- a/Documentation/cpu-freq/intel-pstate.txt
+++ b/Documentation/cpu-freq/intel-pstate.txt
@@ -48,7 +48,7 @@ In addition to the frequency-controlling interfaces provided by the cpufreq
core, the driver provides its own sysfs files to control the P-State selection.
These files have been added to /sys/devices/system/cpu/intel_pstate/.
Any changes made to these files are applicable to all CPUs (even in a
-multi-package system).
+multi-package system, Refer to later section on placing "Per-CPU limits").
max_perf_pct: Limits the maximum P-State that will be requested by
the driver. It states it as a percentage of the available performance. The
@@ -120,6 +120,25 @@ frequency is fictional for Intel Core processors. Even if the scaling
driver selects a single P-State, the actual frequency the processor
will run at is selected by the processor itself.
+Per-CPU limits
+The kernel command line option "intel_pstate=per_cpu_perf_limits" forces
+the intel_pstate driver to use per-CPU performance limits. When it is set,
+the sysfs control interface described above is subject to limitations.
+- The following controls are not available for both read and write
+ /sys/devices/system/cpu/intel_pstate/max_perf_pct
+ /sys/devices/system/cpu/intel_pstate/min_perf_pct
+- The following controls can be used to set performance limits, as far as the
+architecture of the processor permits:
+ /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
Tuning Intel P-State driver
When the performance can be tuned using PID (Proportional Integral