Re: [PATCH V2 2/2] cpufreq: AMD "frequency sensitivity feedback" powersave bias for ondemand governor

Jacob Shin
2013-04-02T17:19:00Z

On Tue, Apr 02, 2013 at 03:42:55PM +0200, Borislav Petkov wrote:
> On Thu, Mar 28, 2013 at 01:24:17PM -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@amd.com>
> > ---
> > arch/x86/include/uapi/asm/msr-index.h | 1 +
> > drivers/cpufreq/Kconfig.x86 | 10 +++
> > drivers/cpufreq/Makefile | 1 +
> > drivers/cpufreq/amd_freq_sensitivity.c | 147 ++++++++++++++++++++++++++++++++
> > 4 files changed, 159 insertions(+)
> > create mode 100644 drivers/cpufreq/amd_freq_sensitivity.c
> >
> > diff --git a/arch/x86/include/uapi/asm/msr-index.h b/arch/x86/include/uapi/asm/msr-index.h
> > index 7a060f4..b2e6c49 100644
> > --- a/arch/x86/include/uapi/asm/msr-index.h
> > +++ b/arch/x86/include/uapi/asm/msr-index.h
> > @@ -173,6 +173,7 @@
> > #define MSR_AMD64_TSC_RATIO 0xc0000104
> > #define MSR_AMD64_NB_CFG 0xc001001f
> > #define MSR_AMD64_PATCH_LOADER 0xc0010020
> > +#define MSR_AMD64_FREQ_SENSITIVITY 0xc0010080
> > #define MSR_AMD64_OSVW_ID_LENGTH 0xc0010140
> > #define MSR_AMD64_OSVW_STATUS 0xc0010141
> > #define MSR_AMD64_DC_CFG 0xc0011022
>
> My guess is, this MSR won't be used outside of cpufreq so you probably
> want to define it there, in amd_freq_sensitivity.c
>
> > diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
> > index d7dc0ed..6c714b0 100644
> > --- a/drivers/cpufreq/Kconfig.x86
> > +++ b/drivers/cpufreq/Kconfig.x86
> > @@ -129,6 +129,16 @@ config X86_POWERNOW_K8
> >
> > For details, take a look at <file:Documentation/cpu-freq/>.
> >
> > +config X86_AMD_FREQ_SENSITIVITY
> > + tristate "AMD 'frequency sensitivity feedback' powersave bias"
>
> Why in ' '? Isn't that the final name?

You are right,

It does not need to be in quotes. I had first written this as its
own governor, and I was mimicking Kconfig entries of 'ondemand',
'performance' .. and so on.

>
> > + depends on CPU_FREQ_GOV_ONDEMAND && X86_ACPI_CPUFREQ
>
> depends on CPU_SUP_AMD
>
> > + help
> > + This adds support for 'frequency sensitivity feedback' feature on
> > + supported AMD processors, which hooks into the ondemand governor's
> > + powersave bias to influence frequency change decisions.
>
> Your description about the feature in the 0/2 message is much better
> than this one here. How about adding it here too?
>
> > +
> > + 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..997feb0
> > --- /dev/null
> > +++ b/drivers/cpufreq/amd_freq_sensitivity.c
> > @@ -0,0 +1,147 @@
> > +/*
> > + * amd_freq_sensitivity.c: AMD "frequency sensitivity feedback" powersave bias
> > + * for ondemand governor.
> > + *
> > + * Copyright (C) 2013 Advanced Micro Devices, Inc.
>
> You probably want to leave an email address in here for contacting you
> when it is b0rked. :-)
>
> > + *
> > + * 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/module.h>
> > +#include <linux/types.h>
> > +#include <linux/percpu-defs.h>
> > +#include <linux/init.h>
> > +
> > +#include "cpufreq_governor.h"
> > +
> > +#define PROC_FEEDBACK_INTERFACE_SHIFT 11
>
> Yeah, that's a bit cumbersome. Just define a normal x86 feature bit in
> cpufeature.h and then you can use static_cpu_has below:
>
> if (!static_cpu_has(AMD_PROC_FEEDBACK_INTERFACE))
> return -ENODEV;
>
>
> > +#define CLASS_CODE_SHIFT 56
> > +#define CLASS_CODE_MASK 0xff
> > +#define CLASS_CODE_CORE_FREQUENCY_SENSITIVITY 0x01
> > +
> > +static u32 msr_addr;
> > +
> > +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)
>
> arg alignment.
>
> > +{
> > + 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);
> > +
> > + rdmsr_on_cpu(policy->cpu, msr_addr, &actual.l, &actual.h);
> > + rdmsr_on_cpu(policy->cpu, msr_addr + 1, &reference.l, &reference.h);
> > + actual.h &= 0x00ffffff;
> > + reference.h &= 0x00ffffff;
> > +
> > + if (!od_info->freq_table)
> > + goto out;
>
> Ok, this check is definitely misplaced. So if we don't have
> ->freq_table, we can save us the MSR accesses above and simply return
> freq_next, right? So basically you want to push the check before the MSR
> accesses and do:
>
> if (!od_info->freq_table)
> return freq_next;

Yup, you are right, my oversight.

>
> Or am I missing something?
>
> > +
> > + /* counter wrapped around, so push until next check */
> > + 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 push as well */
>
> What do you mean by "push as well"? No change, right?

Right, stay at the current frequency. I'll change the comments to be
more clear.

>
> > + if (d_reference == 0) {
> > + freq_next = policy->cur;
> > + goto out;
> > + }
> > +
> > + sensitivity = 1000 - (1000 * (d_reference - d_actual) / d_reference);
>
> Ok, now this naked 1000 could very well use a define here like you do
> for your other values you're using :-).
>
> > + if (sensitivity > 1000)
> > + sensitivity = 1000;
> > + else if (sensitivity < 0)
> > + sensitivity = 0;
>
> clamp(sensitivity, 0, 1000);
>
> > +
> > + /* this workload is not CPU bound, so choose a lower freq */
> > + if (sensitivity < od_tuners->powersave_bias) {
>
> Yeah, this ->powersave_bias usage needs more discussion, as Thomas said
> earlier.
>
> > + 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 = 0;
> > +
> > + 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 i;
> > + u32 eax, edx, dummy;
> > +
> > + if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
> > + return -ENODEV;
> > +
> > + cpuid(0x80000007, &eax, &dummy, &dummy, &edx);
> > +
> > + if (!(edx & (1 << PROC_FEEDBACK_INTERFACE_SHIFT)))
> > + return -ENODEV;
> > +
> > + for (i = 0; i < (eax & 0xf); i++) {
> > + u64 val;
> > + u32 addr = MSR_AMD64_FREQ_SENSITIVITY + (i * 2);
> > +
> > + rdmsrl(addr, val);
>
> Pls use rdmsrl_safe variant for virtualization's sake and check its
> retval befor using it below.
>
> > +
> > + if (((val >> CLASS_CODE_SHIFT) & CLASS_CODE_MASK)
> > + == CLASS_CODE_CORE_FREQUENCY_SENSITIVITY) {
> > + msr_addr = addr;
> > + break;
> > + }
> > + }
>
> What is this thing doing? There's a whole range of MSRs which can give
> you freq feedback? Or only the two as it is done above for actual and
> reference?

Only the two that has to do with frequency sensitivity.

My initial reading of the manual was like this:

* CPUID feature bit says it supports "Processor Feedback Interface"
* Another CPUID field says how many "Number of Monitors" -- actual and
reference MSR register pairs.
* Finally, software can look at all the monitors and see what its
"Class Code" is and 0x01 is the frequency sensitivity.

So I was trying to future proof .. by looking at all possible monitors
and finding the frequency sensitivity.

But I think we can just simplify things and just assume frequency
sensitivity will always live at the defined MSR address. So I'll get
rid of the entire for loop.

>
> Also, you can simplify the check provided that bits [63:56] denote
> support is present if they're not 0:
>
> if (val >> CLASS_CODE_SHIFT)
> msr_addr = addr;
>
> > +
> > + if (!msr_addr)
> > + return -ENODEV;
> > +
> > + od_register_powersave_bias_function(amd_powersave_bias_target);
> > + return 0;
> > +}
> > +module_init(amd_freq_sensitivity_init);
> > +
> > +static void __exit amd_freq_sensitivity_exit(void)
> > +{
> > + od_unregister_powersave_bias_function();
> > +}
> > +module_exit(amd_freq_sensitivity_exit);
> > +
> > +MODULE_AUTHOR("Jacob Shin <jacob.shin@amd.com>");
> > +MODULE_DESCRIPTION("AMD 'frequency sensitivity feedback' powersave bias for "
> > + "the ondemand governor.");
> > +MODULE_LICENSE("GPL");
>
> Thanks.

Thanks for taking a look, I'll send out V3 soon with all your
suggested fixups.

>
> --
> Regards/Gruss,
> Boris.
>
> Sent from a fat crate under my desk. Formatting is fine.
> --
>