The Intel P-state driver is currently undocumented. Add some
documentation based on the cover-letter sent with the original series.
Cc: Dirk Brandewie <[email protected]>
Cc: Rafael J. Wysocki <[email protected]>
Cc: Viresh Kumar <[email protected]>
Signed-off-by: Ramkumar Ramachandra <[email protected]>
---
I was looking for documentation on my cpufreq driver, intel_pstate,
and found nothing: so, here's a small start. Although the original
message said SandyBridge only, I noticed that
/sys/devices/system/cpu/cpu0/cpufreq/scaling_driver says intel_pstate
on my IvyBridge; so I figured subsequent patches introduced support
for SandyBridge+.
I noticed two "policies" in the code: CPUFREQ_POLICY_PERFORMANCE and
CPUFREQ_POLICY_POWERSAVE, but I have no idea how to switch from one
to the other. The userspace tool cpupower seems to be too tightly
tied to the acpi-cpufreq driver, and I'm not able to find any others.
Also, how well is the driver performing? I seem to be getting
terrible battery life on my 2013 MBP.
Thanks.
Documentation/cpu-freq/intel-pstate.txt | 40 +++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)
create mode 100644 Documentation/cpu-freq/intel-pstate.txt
diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
new file mode 100644
index 0000000..fda74ab
--- /dev/null
+++ b/Documentation/cpu-freq/intel-pstate.txt
@@ -0,0 +1,40 @@
+Intel P-state driver
+--------------------
+
+This driver implements a scaling driver with an internal governor for
+Intel Core processors. The driver follows the same model as the
+Transmeta scaling driver (longrun.c) and implements the setpolicy()
+instead of target(). Scaling drivers that implement setpolicy() are
+assmuned to implement internal governors by the cpufreq core. All the
+logic for selecting the current P state is contained within the driver
+no external governor is used by the cpufreq core.
+
+Only Intel SandyBridge+ processors are supported.
+
+New sysfs files for controlling P state selection have been added to
+/sys/devices/system/cpu/intel_pstate/
+
+ max_perf_pct: limits the maximum P state that will be requested by
+ the driver stated as a percentage of the avail performance.
+
+ min_perf_pct: limits the minimum P state that will be requested by
+ the driver stated as a percentage of the avail performance.
+
+ no_turbo: limits the driver to selecting P states below the turbo
+ frequency range.
+
+The units for these for these files are purposely abstract and stated
+in terms of available performance and not frequency. In idea that
+frequency can be set to a single frequency is a fiction 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.
+
+New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
+
+ deadband
+ d_gain_pct
+ i_gain_pct
+ p_gain_pct
+ sample_rate_ms
+ setpoint
--
1.8.5.2.227.g53f3478
On Friday, January 03, 2014 05:01:13 PM Ramkumar Ramachandra wrote:
> The Intel P-state driver is currently undocumented. Add some
> documentation based on the cover-letter sent with the original series.
>
> Cc: Dirk Brandewie <[email protected]>
Dirk, what do you think?
> Cc: Rafael J. Wysocki <[email protected]>
> Cc: Viresh Kumar <[email protected]>
> Signed-off-by: Ramkumar Ramachandra <[email protected]>
> ---
> I was looking for documentation on my cpufreq driver, intel_pstate,
> and found nothing: so, here's a small start. Although the original
> message said SandyBridge only, I noticed that
> /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver says intel_pstate
> on my IvyBridge; so I figured subsequent patches introduced support
> for SandyBridge+.
>
> I noticed two "policies" in the code: CPUFREQ_POLICY_PERFORMANCE and
> CPUFREQ_POLICY_POWERSAVE, but I have no idea how to switch from one
> to the other. The userspace tool cpupower seems to be too tightly
> tied to the acpi-cpufreq driver, and I'm not able to find any others.
>
> Also, how well is the driver performing? I seem to be getting
> terrible battery life on my 2013 MBP.
>
> Thanks.
>
> Documentation/cpu-freq/intel-pstate.txt | 40 +++++++++++++++++++++++++++++++++
> 1 file changed, 40 insertions(+)
> create mode 100644 Documentation/cpu-freq/intel-pstate.txt
>
> diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
> new file mode 100644
> index 0000000..fda74ab
> --- /dev/null
> +++ b/Documentation/cpu-freq/intel-pstate.txt
> @@ -0,0 +1,40 @@
> +Intel P-state driver
> +--------------------
> +
> +This driver implements a scaling driver with an internal governor for
> +Intel Core processors. The driver follows the same model as the
> +Transmeta scaling driver (longrun.c) and implements the setpolicy()
> +instead of target(). Scaling drivers that implement setpolicy() are
> +assmuned to implement internal governors by the cpufreq core. All the
> +logic for selecting the current P state is contained within the driver
> +no external governor is used by the cpufreq core.
> +
> +Only Intel SandyBridge+ processors are supported.
That's not the case any more.
> +
> +New sysfs files for controlling P state selection have been added to
> +/sys/devices/system/cpu/intel_pstate/
> +
> + max_perf_pct: limits the maximum P state that will be requested by
> + the driver stated as a percentage of the avail performance.
> +
> + min_perf_pct: limits the minimum P state that will be requested by
> + the driver stated as a percentage of the avail performance.
> +
> + no_turbo: limits the driver to selecting P states below the turbo
> + frequency range.
> +
It would be good to document them in Documentation/ABI/testing/ as well.
> +The units for these for these files are purposely abstract and stated
> +in terms of available performance and not frequency. In idea that
I would say "For contemporary Intel processor the frequency is controlled
by the processor itself and the P-states exposed to software are related to
performance levels" instead.
> +frequency can be set to a single frequency is a fiction 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.
> +
> +New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
> +
> + deadband
> + d_gain_pct
> + i_gain_pct
> + p_gain_pct
> + sample_rate_ms
> + setpoint
>
Thanks!
--
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
On 01/03/14 03:31, Ramkumar Ramachandra wrote:
> The Intel P-state driver is currently undocumented. Add some
> documentation based on the cover-letter sent with the original series.
>
> Cc: Dirk Brandewie <[email protected]>
> Cc: Rafael J. Wysocki <[email protected]>
> Cc: Viresh Kumar <[email protected]>
> Signed-off-by: Ramkumar Ramachandra <[email protected]>
> ---
>
> Documentation/cpu-freq/intel-pstate.txt | 40 +++++++++++++++++++++++++++++++++
> 1 file changed, 40 insertions(+)
> create mode 100644 Documentation/cpu-freq/intel-pstate.txt
>
> diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
> new file mode 100644
> index 0000000..fda74ab
> --- /dev/null
> +++ b/Documentation/cpu-freq/intel-pstate.txt
> @@ -0,0 +1,40 @@
> +Intel P-state driver
> +--------------------
> +
> +This driver implements a scaling driver with an internal governor for
> +Intel Core processors. The driver follows the same model as the
> +Transmeta scaling driver (longrun.c) and implements the setpolicy()
> +instead of target(). Scaling drivers that implement setpolicy() are
> +assmuned to implement internal governors by the cpufreq core. All the
assumed
> +logic for selecting the current P state is contained within the driver
driver;
> +no external governor is used by the cpufreq core.
> +
> +Only Intel SandyBridge+ processors are supported.
> +
> +New sysfs files for controlling P state selection have been added to
> +/sys/devices/system/cpu/intel_pstate/
> +
> + max_perf_pct: limits the maximum P state that will be requested by
> + the driver stated as a percentage of the avail performance.
available
> +
> + min_perf_pct: limits the minimum P state that will be requested by
> + the driver stated as a percentage of the avail performance.
available
> +
> + no_turbo: limits the driver to selecting P states below the turbo
> + frequency range.
> +
> +The units for these for these files are purposely abstract and stated
drop duplicate "for these"
> +in terms of available performance and not frequency. In idea that
The idea
> +frequency can be set to a single frequency is a fiction for Intel Core
is fiction
> +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.
> +
> +New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
> +
> + deadband
> + d_gain_pct
> + i_gain_pct
> + p_gain_pct
> + sample_rate_ms
> + setpoint
>
--
~Randy
On 01/03/2014 04:09 AM, Rafael J. Wysocki wrote:
> On Friday, January 03, 2014 05:01:13 PM Ramkumar Ramachandra wrote:
>> The Intel P-state driver is currently undocumented. Add some
>> documentation based on the cover-letter sent with the original series.
>>
>> Cc: Dirk Brandewie <[email protected]>
>
> Dirk, what do you think?
>
This is accurate, along with the wording changes suggested by you and
Randy,
>> Cc: Rafael J. Wysocki <[email protected]>
>> Cc: Viresh Kumar <[email protected]>
>> Signed-off-by: Ramkumar Ramachandra <[email protected]>
>> ---
>> I was looking for documentation on my cpufreq driver, intel_pstate,
>> and found nothing: so, here's a small start. Although the original
>> message said SandyBridge only, I noticed that
>> /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver says intel_pstate
>> on my IvyBridge; so I figured subsequent patches introduced support
>> for SandyBridge+.
>>
>> I noticed two "policies" in the code: CPUFREQ_POLICY_PERFORMANCE and
>> CPUFREQ_POLICY_POWERSAVE, but I have no idea how to switch from one
>> to the other. The userspace tool cpupower seems to be too tightly
>> tied to the acpi-cpufreq driver, and I'm not able to find any others.
>>
>> Also, how well is the driver performing? I seem to be getting
>> terrible battery life on my 2013 MBP.
>>
>> Thanks.
>>
>> Documentation/cpu-freq/intel-pstate.txt | 40 +++++++++++++++++++++++++++++++++
>> 1 file changed, 40 insertions(+)
>> create mode 100644 Documentation/cpu-freq/intel-pstate.txt
>>
>> diff --git a/Documentation/cpu-freq/intel-pstate.txt b/Documentation/cpu-freq/intel-pstate.txt
>> new file mode 100644
>> index 0000000..fda74ab
>> --- /dev/null
>> +++ b/Documentation/cpu-freq/intel-pstate.txt
>> @@ -0,0 +1,40 @@
>> +Intel P-state driver
>> +--------------------
>> +
>> +This driver implements a scaling driver with an internal governor for
>> +Intel Core processors. The driver follows the same model as the
>> +Transmeta scaling driver (longrun.c) and implements the setpolicy()
>> +instead of target(). Scaling drivers that implement setpolicy() are
>> +assmuned to implement internal governors by the cpufreq core. All the
>> +logic for selecting the current P state is contained within the driver
>> +no external governor is used by the cpufreq core.
>> +
>> +Only Intel SandyBridge+ processors are supported.
>
> That's not the case any more.
SandyBridge+ is accurate "only SandyBridge" is not
>
>> +
>> +New sysfs files for controlling P state selection have been added to
>> +/sys/devices/system/cpu/intel_pstate/
>> +
>> + max_perf_pct: limits the maximum P state that will be requested by
>> + the driver stated as a percentage of the avail performance.
>> +
>> + min_perf_pct: limits the minimum P state that will be requested by
>> + the driver stated as a percentage of the avail performance.
>> +
>> + no_turbo: limits the driver to selecting P states below the turbo
>> + frequency range.
>> +
>
> It would be good to document them in Documentation/ABI/testing/ as well.
>
>> +The units for these for these files are purposely abstract and stated
>> +in terms of available performance and not frequency. In idea that
>
> I would say "For contemporary Intel processor the frequency is controlled
> by the processor itself and the P-states exposed to software are related to
> performance levels" instead.
>
>> +frequency can be set to a single frequency is a fiction 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.
>> +
>> +New debugfs files have also been added to /sys/kernel/debug/pstate_snb/
>> +
>> + deadband
>> + d_gain_pct
>> + i_gain_pct
>> + p_gain_pct
>> + sample_rate_ms
>> + setpoint
>>
>
> Thanks!
>