[CPUFREQ][8/8] acpi-cpufreq: Add support for freq feedback from hardware

Enable ondemand governor and acpi-cpufreq to use IA32_APERF and IA32_MPERF MSR
to get active frequency feedback for the last sampling interval. This will
make ondemand take right frequency decisions when hardware coordination of
frequency is going on.

Without APERF/MPERF, ondemand can take wrong decision at times due
to underlying hardware coordination or TM2.
Example:
* CPU 0 and CPU 1 are hardware cooridnated.
* CPU 1 running at highest frequency.
* CPU 0 was running at highest freq. Now ondemand reduces it to
  some intermediate frequency based on utilization.
* Due to underlying hardware coordination with other CPU 1, CPU 0 continues to
  run at highest frequency (as long as other CPU is at highest).
* When ondemand samples CPU 0 again next time, without actual frequency
  feedback from APERF/MPERF, it will think that previous frequency change
  was successful and can go to wrong target frequency. This is because it
  thinks that utilization it has got this sampling interval is when running at
  intermediate frequency, rather than actual highest frequency.

More information about IA32_APERF IA32_MPERF MSR:
Refer to IA-32 Intel® Architecture Software Developer's Manual at
http://developer.intel.com

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Dave Jones <davej@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 4ea39fee99c7..7f008f6bfdc3 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -172,6 +172,8 @@ extern int __cpufreq_driver_target(struct cpufreq_policy *policy,
                                    unsigned int relation);
 
 
+extern int cpufreq_driver_getavg(struct cpufreq_policy *policy);
+
 int cpufreq_register_governor(struct cpufreq_governor *governor);
 void cpufreq_unregister_governor(struct cpufreq_governor *governor);
 
@@ -204,6 +206,7 @@ struct cpufreq_driver {
         unsigned int    (*get)  (unsigned int cpu);
 
         /* optional */
+        unsigned int (*getavg)  (unsigned int cpu);
         int     (*exit)         (struct cpufreq_policy *policy);
         int     (*suspend)      (struct cpufreq_policy *policy, pm_message_t pmsg);
         int     (*resume)       (struct cpufreq_policy *policy);