[PATCH] cpufreq: intel_pstate: Clarify effective CPU frequency
From: Srinivas Pandruvada
Date: Wed Oct 04 2017 - 18:46:31 EST
Add section for resultant frequency during GPU workloads.
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Documentation/admin-guide/pm/intel_pstate.rst | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/Documentation/admin-guide/pm/intel_pstate.rst b/Documentation/admin-guide/pm/intel_pstate.rst
index d2b6fda..a7c6308 100644
@@ -482,6 +482,25 @@ on the following rules, regardless of the current operation mode of the driver:
3. The global and per-policy limits can be set independently.
+One important point to note is that all the above limit controls including
+``no_turbo``, only limits the P-state requests by the intel_pstate driver. The
+actual performance delivered by the processor is also influenced by GPU
+(Graphics processing unit) for GPU bound workloads. So, it is possible
+that, while GPU is requesting higher frequencies, the resultant P-state
+(CPU frequency) can be higher than the limits set via sysfs.
+Equivalent limits must, therefore, also be set for the GPU.
+An example where an Intel i915 GPU is used:
+displays effective CPU frequency for a GPU frequency. To limit
+a CPU frequency, a corresponding GPU frequency limit must also be placed:
If the `HWP feature is enabled in the processor <Active Mode With HWP_>`_, the
resulting effective values are written into its registers whenever the limits
change in order to request its internal P-state selection logic to always set