From: Dirk Brandewie <dirk.brandewie@xxxxxxxxx>
This driver provides a P state driver for Sandybridge and Ivybridge
processors.
Motivation:
The goal of this driver is to improve the power efficiency of
Sandybridge/Ivybridge based systems. As the investigation into how to
achieve this goal progressed it became apparent (to me) that some of the
design assumptions of the cpufreq subsystem are no longer valid and
that a micro-architecure specific P state driver would be less complex
and potentially more effiecent. As Intel continues to innovate in the
area of freqency/power control this will become more true IMHO.
General info:
The driver uses a PID controller to adjust the core frequency based on
the presented load. The driver exposes the tuning parameters for the
controller in the /sys/devices/system/cpu/cpufreq/snb directory. The
controller code is being used in PI mode with the default tuning
parmeters.
Tuning parmeters:
setpoint - load in percent on the core will attempt to maintain.
sample_rate_ms - rate at which the driver will sample the load on the core.
deadband - percent ± around the setpoint the controller will
consider zero error.
p_gain_pct - Proportional gain in percent.
i_gain_pct - Integral gain in percent.
d_gain_pct - Derivative gain in percent
To use the driver as root run the following shell script:
#!/bin/sh
for file in /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
do
echo snb > $file
done
Limitations:
ATM this driver will only run on SandyBridge systems testing on
Ivybridge systems is not complete.
Open Questions:
What is the correct way to integrate this driver into the system? The
current implementation registers as a cpufreq frequency governor, this
was done to streamline testing using cpufreq to load/unload governors.
What tuning parameters should be exposed via sysfs (if any)? ATM all
the PID parameters are exposed to enable tuning of the driver.
Performance information:
--- Kernel build ---
The following is data collected for a bzImage kernel build. The
commands used were:
make -j8 clean
sysctl -w vm.drop_caches=3
/usr/bin/time -f "%E %c" make -j8 bzImage
Time and context switches measured with /usr/bin/time -f "%E %c"
Energy measured with package energy status MSR described in section
14.7 in the Intel® 64 and IA-32 Architectures Software Developer’s
Manual Volume 3.
http://download.intel.com/products/processor/manual/325384.pdf
Average watts calculated with energy/time in seconds
time ctx sw energy avg watts
perf 02:24.49 116721 6660 46.09
snb 02:27.03 114940 6591 44.83
ondemand 02:26.83 190948 6683 45.51
A graph of the power usage during the kernel build for each governor
is available here:
http://git.fenrus.org/dirk/kernel.png
--- Power benchmark ---
I used industry standard power bench suite to compare the performance and
ondemand governors against the Sandybridge governor.
Governor | ssj_ops/watt
-----------------------------
performance | 1855
ondemand | 1839
snb | 2016
A graph of the power usage for each governor is avavailable here:
http://git.fenrus.org/dirk/power_benchmark.png
A graph showing the results of cpufreq-bench tool shipped with the
kernel Collected with
cpufreq-bench -l 6000 -s 6000 -x 2000 -y 2000 -c 0 \
-g {ondemand | snb} -n 40 -r 40
is available here:
http://git.fenrus.org/dirk/cpufreq-bench.png
Dirk Brandewie (1):
cpufreq/x86: Add P-state driver for sandy bridge.
drivers/cpufreq/Kconfig.x86 | 8 +
drivers/cpufreq/Makefile | 1 +
drivers/cpufreq/cpufreq_snb.c | 727 +++++++++++++++++++++++++++++++++++++++++
3 files changed, 736 insertions(+), 0 deletions(-)
create mode 100644 drivers/cpufreq/cpufreq_snb.c
--
1.7.7.6
--
To unsubscribe from this list: send the line "unsubscribe cpufreq" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
