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Date: Wed, 24 Jun 2020 08:37:23 -0700
From: "Doug Smythies" <dsmythies@...us.net>
To: "'Srinivas Pandruvada'" <srinivas.pandruvada@...ux.intel.com>
Cc: <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<rjw@...ysocki.net>, <viresh.kumar@...aro.org>, <lenb@...nel.org>
Subject: RE: [PATCH v2 2/2] cpufreq: intel_pstate: Allow raw energy performance preference value
Hi Srinivas,
I have immediate need for this. I have been using a tool
I wrote myself for this which I can now retire.
(it wasn't very good anyway).
Yours remembers for each governor, and is way better.
Thanks.
On 2020.06.23 11:27 Srinivas Pandruvada wrote:
> Currently using attribute "energy_performance_preference", user space can
> write one of the four per-defined preference string. These preference
> strings gets mapped to a hard-coded Energy-Performance Preference (EPP) or
> Energy-Performance Bias (EPB) knob.
>
> These four values supposed to cover broad spectrum of use cases, but they
> are not uniformly distributed in the range.
Suggest:
These four values are supposed to cover broad spectrum of use cases, but
are not uniformly distributed in the range.
> There are number of cases,
> where this is not enough. For example:
>
> Suppose user wants more performance when connected to AC. Instead of using
> default "balance performance", the "performance" setting can be used. This
> changes EPP value from 0x80 to 0x00. But setting EPP to 0, results in
> electrical and thermal issues on some platforms.
> This results in CPU to do
> aggressive throttling, which causes drop in performance.
Suggest:
This results in aggressive throttling, which causes a drop in performance.
And:
Tough.
I consider "performance mode" as sacrosanct, and have always
expected these to behave identically and at max CPU freq:
intel_pstate no-hwp / performance
intel_cpufreq no-hwp / performance (a.k.a. passive)
acpi_cpufreq / performance
intel_pstate hwp / performance
intel_cpufreq hwp / performance (in future)
as was always the case on my i7-2600K (no hwp) based computer
and is not the case on my i5-9600K (hwp capable) computer.
> But some value
> between 0x80 and 0x00 results in better performance. But that value can't
> be fixed as the power curve is not linear. In some cases just changing EPP
> from 0x80 to 0x75 is enough to get significant performance gain.
>
> Similarly on battery EPP 0x80 can be very aggressive in power consumption.
> But picking up the next choice "balance power" results in too much loss
> of performance, which cause bad user experience in use case like "Google
> Hangout". It was observed that some value between these two EPP is
> optimal.
>
> This change allows fine grain EPP tuning for platform like Chromebooks.
> Here based on the product and use cases, different EPP values can be set.
> This change is similar to the change done for:
> /sys/devices/system/cpu/cpu*/power/energy_perf_bias
> where user has choice to write a predefined string or raw value.
>
> The change itself is trivial. When user preference doesn't match
> predefined string preferences and value is an unsigned integer and in
> range, use that value for EPP. When the EPP feature is not prsent
^^^^^^
s/prsent/present
> writing raw value is not supported.
>
> Suggested-by: Len Brown <lenb@...nel.org>
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
> ---
> Documentation/admin-guide/pm/intel_pstate.rst | 6 ++-
> drivers/cpufreq/intel_pstate.c | 50 +++++++++++++++----
> 2 files changed, 45 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/admin-guide/pm/intel_pstate.rst b/Documentation/admin-
> guide/pm/intel_pstate.rst
> index 939bfdc53f4f..5e209926e0ed 100644
> --- a/Documentation/admin-guide/pm/intel_pstate.rst
> +++ b/Documentation/admin-guide/pm/intel_pstate.rst
> @@ -561,7 +561,11 @@ somewhere between the two extremes:
> Strings written to the ``energy_performance_preference`` attribute are
> internally translated to integer values written to the processor's
> Energy-Performance Preference (EPP) knob (if supported) or its
> -Energy-Performance Bias (EPB) knob.
> +Energy-Performance Bias (EPB) knob. It is also possible to write a positive
> +integer value between 0 to 255, if the EPP feature is present. If the EPP
> +feature is not present, writing integer value to this attribute is not
> +supported. In this case, user can use
> + "/sys/devices/system/cpu/cpu*/power/energy_perf_bias" interface.
>
> [Note that tasks may by migrated from one CPU to another by the scheduler's
> load-balancing algorithm and if different energy vs performance hints are
> diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
> index 1cf6d06f2314..d8f195c7a428 100644
> --- a/drivers/cpufreq/intel_pstate.c
> +++ b/drivers/cpufreq/intel_pstate.c
> @@ -602,11 +602,12 @@ static const unsigned int epp_values[] = {
> HWP_EPP_POWERSAVE
> };
>
> -static int intel_pstate_get_energy_pref_index(struct cpudata *cpu_data)
> +static int intel_pstate_get_energy_pref_index(struct cpudata *cpu_data, int *raw_epp)
> {
> s16 epp;
> int index = -EINVAL;
>
> + *raw_epp = 0;
> epp = intel_pstate_get_epp(cpu_data, 0);
> if (epp < 0)
> return epp;
> @@ -614,12 +615,14 @@ static int intel_pstate_get_energy_pref_index(struct cpudata *cpu_data)
> if (boot_cpu_has(X86_FEATURE_HWP_EPP)) {
> if (epp == HWP_EPP_PERFORMANCE)
> return 1;
> - if (epp <= HWP_EPP_BALANCE_PERFORMANCE)
> + if (epp == HWP_EPP_BALANCE_PERFORMANCE)
> return 2;
> - if (epp <= HWP_EPP_BALANCE_POWERSAVE)
> + if (epp == HWP_EPP_BALANCE_POWERSAVE)
> return 3;
> - else
> + if (epp == HWP_EPP_POWERSAVE)
> return 4;
> + *raw_epp = epp;
> + return 0;
> } else if (boot_cpu_has(X86_FEATURE_EPB)) {
> /*
> * Range:
> @@ -638,7 +641,8 @@ static int intel_pstate_get_energy_pref_index(struct cpudata *cpu_data)
> }
>
> static int intel_pstate_set_energy_pref_index(struct cpudata *cpu_data,
> - int pref_index)
> + int pref_index, bool use_raw,
> + u32 raw_epp)
> {
> int epp = -EINVAL;
> int ret;
> @@ -657,6 +661,16 @@ static int intel_pstate_set_energy_pref_index(struct cpudata *cpu_data,
>
> value &= ~GENMASK_ULL(31, 24);
>
> + if (use_raw) {
> + if (raw_epp > 255) {
> + ret = -EINVAL;
> + goto return_pref;
> + }
> + value |= (u64)raw_epp << 24;
> + ret = wrmsrl_on_cpu(cpu_data->cpu, MSR_HWP_REQUEST, value);
> + goto return_pref;
> + }
> +
> if (epp == -EINVAL)
> epp = epp_values[pref_index - 1];
>
> @@ -694,6 +708,8 @@ static ssize_t store_energy_performance_preference(
> {
> struct cpudata *cpu_data = all_cpu_data[policy->cpu];
> char str_preference[21];
> + bool raw = false;
> + u32 epp;
> int ret;
>
> ret = sscanf(buf, "%20s", str_preference);
> @@ -701,10 +717,21 @@ static ssize_t store_energy_performance_preference(
> return -EINVAL;
>
> ret = match_string(energy_perf_strings, -1, str_preference);
> - if (ret < 0)
> + if (ret < 0) {
> + if (!boot_cpu_has(X86_FEATURE_HWP_EPP))
> + return ret;
> +
> + ret = kstrtouint(buf, 10, &epp);
> + if (ret)
> + return ret;
> +
> + raw = true;
> + }
> +
> + ret = intel_pstate_set_energy_pref_index(cpu_data, ret, raw, epp);
> + if (ret)
> return ret;
>
> - intel_pstate_set_energy_pref_index(cpu_data, ret);
> return count;
> }
>
> @@ -712,13 +739,16 @@ static ssize_t show_energy_performance_preference(
> struct cpufreq_policy *policy, char *buf)
> {
> struct cpudata *cpu_data = all_cpu_data[policy->cpu];
> - int preference;
> + int preference, raw_epp;
>
> - preference = intel_pstate_get_energy_pref_index(cpu_data);
> + preference = intel_pstate_get_energy_pref_index(cpu_data, &raw_epp);
> if (preference < 0)
> return preference;
>
> - return sprintf(buf, "%s\n", energy_perf_strings[preference]);
> + if (raw_epp)
> + return sprintf(buf, "%d\n", raw_epp);
> + else
> + return sprintf(buf, "%s\n", energy_perf_strings[preference]);
> }
>
> cpufreq_freq_attr_rw(energy_performance_preference);
> --
> 2.25.4
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