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Date: Tue, 2 Apr 2013 21:23:52 +0200
From: Borislav Petkov <bp@...en8.de>
To: Jacob Shin <jacob.shin@....com>
Cc: "Rafael J. Wysocki" <rjw@...k.pl>, cpufreq@...r.kernel.org,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
Viresh Kumar <viresh.kumar@...aro.org>,
Thomas Renninger <trenn@...e.de>
Subject: Re: [PATCH V3 2/2] cpufreq: AMD "frequency sensitivity feedback"
powersave bias for ondemand governor
On Tue, Apr 02, 2013 at 01:11:44PM -0500, Jacob Shin wrote:
> Future AMD processors, starting with Family 16h, can provide software
> with feedback on how the workload may respond to frequency change --
> memory-bound workloads will not benefit from higher frequency, where
> as compute-bound workloads will. This patch enables this "frequency
> sensitivity feedback" to aid the ondemand governor to make better
> frequency change decisions by hooking into the powersave bias.
>
> Signed-off-by: Jacob Shin <jacob.shin@....com>
> ---
[ … ]
> --- a/drivers/cpufreq/Kconfig.x86
> +++ b/drivers/cpufreq/Kconfig.x86
> @@ -129,6 +129,23 @@ config X86_POWERNOW_K8
>
> For details, take a look at <file:Documentation/cpu-freq/>.
>
> +config X86_AMD_FREQ_SENSITIVITY
/me is turning on his spell checker...
> + tristate "AMD frequency sensitivity feedback powersave bias"
> + depends on CPU_FREQ_GOV_ONDEMAND && X86_ACPI_CPUFREQ && CPU_SUP_AMD
> + help
> + This adds AMD specific powersave bias function to the ondemand
AMD-specific
> + governor; which can be used to help ondemand governor make more power
"... governor, which allows it to make more power-conscious frequency
change decisions based on ..."
> + conscious frequency change decisions based on feedback from hardware
> + (availble on AMD Family 16h and above).
s/availble/available/
> +
> + Hardware feedback tells software how "sensitive" to frequency changes
> + the CPUs' workloads are. CPU-bound workloads will be more sensitive
> + -- they will perform better as frequency increases. Memory/IO-bound
> + workloads will be less sensitive -- they will not necessarily perform
> + better as frequnecy increases.
s/frequnecy/frequency/
> +
> + If in doubt, say N.
> +
> config X86_GX_SUSPMOD
> tristate "Cyrix MediaGX/NatSemi Geode Suspend Modulation"
> depends on X86_32 && PCI
> diff --git a/drivers/cpufreq/Makefile b/drivers/cpufreq/Makefile
> index 863fd18..01dfdaf 100644
> --- a/drivers/cpufreq/Makefile
> +++ b/drivers/cpufreq/Makefile
> @@ -41,6 +41,7 @@ obj-$(CONFIG_X86_SPEEDSTEP_CENTRINO) += speedstep-centrino.o
> obj-$(CONFIG_X86_P4_CLOCKMOD) += p4-clockmod.o
> obj-$(CONFIG_X86_CPUFREQ_NFORCE2) += cpufreq-nforce2.o
> obj-$(CONFIG_X86_INTEL_PSTATE) += intel_pstate.o
> +obj-$(CONFIG_X86_AMD_FREQ_SENSITIVITY) += amd_freq_sensitivity.o
>
> ##################################################################################
> # ARM SoC drivers
> diff --git a/drivers/cpufreq/amd_freq_sensitivity.c b/drivers/cpufreq/amd_freq_sensitivity.c
> new file mode 100644
> index 0000000..e3e62d2
> --- /dev/null
> +++ b/drivers/cpufreq/amd_freq_sensitivity.c
> @@ -0,0 +1,150 @@
> +/*
> + * amd_freq_sensitivity.c: AMD frequency sensitivity feedback powersave bias
> + * for the ondemand governor.
> + *
> + * Copyright (C) 2013 Advanced Micro Devices, Inc.
> + *
> + * Author: Jacob Shin <jacob.shin@....com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/types.h>
> +#include <linux/percpu-defs.h>
> +#include <linux/init.h>
> +#include <linux/mod_devicetable.h>
> +
> +#include <asm/msr.h>
> +#include <asm/cpufeature.h>
> +
> +#include "cpufreq_governor.h"
> +
> +#define MSR_AMD64_FREQ_SENSITIVITY_ACTUAL 0xc0010080
> +#define MSR_AMD64_FREQ_SENSITIVITY_REFERENCE 0xc0010081
> +#define CLASS_CODE_SHIFT 56
> +#define CLASS_CODE_CORE_FREQ_SENSITIVITY 0x01
> +#define POWERSAVE_BIAS_MAX 1000
> +
> +struct cpu_data_t {
> + u64 actual;
> + u64 reference;
> + unsigned int freq_prev;
> +};
> +
> +static DEFINE_PER_CPU(struct cpu_data_t, cpu_data);
> +
> +static unsigned int amd_powersave_bias_target(struct cpufreq_policy *policy,
> + unsigned int freq_next,
> + unsigned int relation)
> +{
> + int sensitivity;
> + long d_actual, d_reference;
> + struct msr actual, reference;
> + struct cpu_data_t *data = &per_cpu(cpu_data, policy->cpu);
> + struct dbs_data *od_data = policy->governor_data;
> + struct od_dbs_tuners *od_tuners = od_data->tuners;
> + struct od_cpu_dbs_info_s *od_info =
> + od_data->cdata->get_cpu_dbs_info_s(policy->cpu);
> +
> + if (!od_info->freq_table)
> + return freq_next;
> +
> + rdmsr_on_cpu(policy->cpu, MSR_AMD64_FREQ_SENSITIVITY_ACTUAL,
> + &actual.l, &actual.h);
> + rdmsr_on_cpu(policy->cpu, MSR_AMD64_FREQ_SENSITIVITY_REFERENCE,
> + &reference.l, &reference.h);
> + actual.h &= 0x00ffffff;
> + reference.h &= 0x00ffffff;
> +
> + /* counter wrapped around, so stay on current frequency */
> + if (actual.q < data->actual || reference.q < data->reference) {
> + freq_next = policy->cur;
> + goto out;
> + }
> +
> + d_actual = actual.q - data->actual;
> + d_reference = reference.q - data->reference;
> +
> + /* divide by 0, so stay on current frequency as well */
> + if (d_reference == 0) {
> + freq_next = policy->cur;
> + goto out;
> + }
> +
> + sensitivity = POWERSAVE_BIAS_MAX -
> + (POWERSAVE_BIAS_MAX * (d_reference - d_actual) / d_reference);
> +
> + clamp(sensitivity, 0, POWERSAVE_BIAS_MAX);
> +
> + /* this workload is not CPU bound, so choose a lower freq */
> + if (sensitivity < od_tuners->powersave_bias) {
Ok, I still didn't get an answer to that: don't we want to use this
feature by default, even without looking at ->powersave_bias? I mean,
with feedback from the hardware, we kinda know better than the user, no?
> + if (data->freq_prev == policy->cur)
> + freq_next = policy->cur;
> +
> + if (freq_next > policy->cur)
> + freq_next = policy->cur;
> + else if (freq_next < policy->cur)
> + freq_next = policy->min;
> + else {
> + unsigned int index;
> +
> + cpufreq_frequency_table_target(policy,
> + od_info->freq_table, policy->cur - 1,
> + CPUFREQ_RELATION_H, &index);
> + freq_next = od_info->freq_table[index].frequency;
> + }
> +
> + data->freq_prev = freq_next;
> + } else
> + data->freq_prev = 0;
> +
> +out:
> + data->actual = actual.q;
> + data->reference = reference.q;
> + return freq_next;
> +}
> +
> +static int __init amd_freq_sensitivity_init(void)
> +{
> + int err;
> + u64 val;
> +
> + if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
> + return -ENODEV;
> +
> + if (!static_cpu_has(X86_FEATURE_PROC_FEEDBACK))
> + return -ENODEV;
> +
> + err = rdmsrl_safe(MSR_AMD64_FREQ_SENSITIVITY_ACTUAL, &val);
> +
extraneous newline.
> + if (err)
> + return -ENODEV;
> +
> + if ((val >> CLASS_CODE_SHIFT) != CLASS_CODE_CORE_FREQ_SENSITIVITY)
> + return -ENODEV;
If this CLASS_CODE_CORE_FREQ_SENSITIVITY is always going to be a
non-null value, you can simplify the check even more, as I proposed
earlier:
if (val >> CLASS_CODE_SHIFT)
...
and drop CLASS_CODE_CORE_FREQ_SENSITIVITY.
Thanks.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
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