Date:	Tue, 2 Apr 2013 12:18:50 -0500
From:	Jacob Shin <jacob.shin@....com>
To:	Borislav Petkov <bp@...en8.de>, "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>
Subject: Re: [PATCH V2 2/2] cpufreq: AMD "frequency sensitivity feedback"
 powersave bias for ondemand governor

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@....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@....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.
> --
> 

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