acpi-cpufreq: Add support for disabling dynamic overclocking

		All AMD processors with L3 caches provide this functionality.

		For details, see BKDGs at

		http://developer.amd.com/documentation/guides/Pages/default.aspx

What:		/sys/devices/system/cpu/cpufreq/boost

Date:		August 2012

Contact:	Linux kernel mailing list <linux-kernel@vger.kernel.org>

Description:	Processor frequency boosting control

		This switch controls the boost setting for the whole system.

		Boosting allows the CPU and the firmware to run at a frequency

		beyound it's nominal limit.

		More details can be found in Documentation/cpu-freq/boost.txt

Processor boosting control

	- information for users -

Quick guide for the impatient:

--------------------

/sys/devices/system/cpu/cpufreq/boost

controls the boost setting for the whole system. You can read and write

that file with either "0" (boosting disabled) or "1" (boosting allowed).

Reading or writing 1 does not mean that the system is boosting at this

very moment, but only that the CPU _may_ raise the frequency at it's

discretion.

--------------------

Introduction

-------------

Some CPUs support a functionality to raise the operating frequency of

some cores in a multi-core package if certain conditions apply, mostly

if the whole chip is not fully utilized and below it's intended thermal

budget. This is done without operating system control by a combination

of hardware and firmware.

On Intel CPUs this is called "Turbo Boost", AMD calls it "Turbo-Core",

in technical documentation "Core performance boost". In Linux we use

the term "boost" for convenience.

Rationale for disable switch

----------------------------

Though the idea is to just give better performance without any user

intervention, sometimes the need arises to disable this functionality.

Most systems offer a switch in the (BIOS) firmware to disable the

functionality at all, but a more fine-grained and dynamic control would

be desirable:

1. While running benchmarks, reproducible results are important. Since

   the boosting functionality depends on the load of the whole package,

   single thread performance can vary. By explicitly disabling the boost

   functionality at least for the benchmark's run-time the system will run

   at a fixed frequency and results are reproducible again.

2. To examine the impact of the boosting functionality it is helpful

   to do tests with and without boosting.

3. Boosting means overclocking the processor, though under controlled

   conditions. By raising the frequency and the voltage the processor

   will consume more power than without the boosting, which may be

   undesirable for instance for mobile users. Disabling boosting may

   save power here, though this depends on the workload.

User controlled switch

----------------------

To allow the user to toggle the boosting functionality, the acpi-cpufreq

driver exports a sysfs knob to disable it. There is a file:

/sys/devices/system/cpu/cpufreq/boost

which can either read "0" (boosting disabled) or "1" (boosting enabled).

Reading the file is always supported, even if the processor does not

support boosting. In this case the file will be read-only and always

reads as "0". Explicitly changing the permissions and writing to that

file anyway will return EINVAL.

On supported CPUs one can write either a "0" or a "1" into this file.

This will either disable the boost functionality on all cores in the

whole system (0) or will allow the hardware to boost at will (1).

Writing a "1" does not explicitly boost the system, but just allows the

CPU (and the firmware) to boost at their discretion. Some implementations

take external factors like the chip's temperature into account, so

boosting once does not necessarily mean that it will occur every time

even using the exact same software setup.

AMD legacy cpb switch

---------------------

The AMD powernow-k8 driver used to support a very similar switch to

disable or enable the "Core Performance Boost" feature of some AMD CPUs.

This switch was instantiated in each CPU's cpufreq directory

(/sys/devices/system/cpu[0-9]*/cpufreq) and was called "cpb".

Though the per CPU existence hints at a more fine grained control, the

actual implementation only supported a system-global switch semantics,

which was simply reflected into each CPU's file. Writing a 0 or 1 into it

would pull the other CPUs to the same state.

For compatibility reasons this file and its behavior is still supported

on AMD CPUs, though it is now protected by a config switch

(X86_ACPI_CPUFREQ_CPB). On Intel CPUs this file will never be created,

even with the config option set.

This functionality is considered legacy and will be removed in some future

kernel version.

More fine grained boosting control

----------------------------------

Technically it is possible to switch the boosting functionality at least

on a per package basis, for some CPUs even per core. Currently the driver

does not support it, but this may be implemented in the future.

#define INTEL_MSR_RANGE		(0xffff)

#define AMD_MSR_RANGE		(0x7)

#define MSR_K7_HWCR_CPB_DIS	(1ULL << 25)

struct acpi_cpufreq_data {

	struct acpi_processor_performance *acpi_data;

	struct cpufreq_frequency_table *freq_table;

static struct cpufreq_driver acpi_cpufreq_driver;

static unsigned int acpi_pstate_strict;

static bool boost_enabled, boost_supported;

static struct msr __percpu *msrs;

static bool boost_state(unsigned int cpu)

{

	u32 lo, hi;

	u64 msr;

	switch (boot_cpu_data.x86_vendor) {

	case X86_VENDOR_INTEL:

		rdmsr_on_cpu(cpu, MSR_IA32_MISC_ENABLE, &lo, &hi);

		msr = lo | ((u64)hi << 32);

		return !(msr & MSR_IA32_MISC_ENABLE_TURBO_DISABLE);

	case X86_VENDOR_AMD:

		rdmsr_on_cpu(cpu, MSR_K7_HWCR, &lo, &hi);

		msr = lo | ((u64)hi << 32);

		return !(msr & MSR_K7_HWCR_CPB_DIS);

	}

	return false;

}

static void boost_set_msrs(bool enable, const struct cpumask *cpumask)

{

	u32 cpu;

	u32 msr_addr;

	u64 msr_mask;

	switch (boot_cpu_data.x86_vendor) {

	case X86_VENDOR_INTEL:

		msr_addr = MSR_IA32_MISC_ENABLE;

		msr_mask = MSR_IA32_MISC_ENABLE_TURBO_DISABLE;

		break;

	case X86_VENDOR_AMD:

		msr_addr = MSR_K7_HWCR;

		msr_mask = MSR_K7_HWCR_CPB_DIS;

		break;

	default:

		return;

	}

	rdmsr_on_cpus(cpumask, msr_addr, msrs);

	for_each_cpu(cpu, cpumask) {

		struct msr *reg = per_cpu_ptr(msrs, cpu);

		if (enable)

			reg->q &= ~msr_mask;

		else

			reg->q |= msr_mask;

	}

	wrmsr_on_cpus(cpumask, msr_addr, msrs);

}

static ssize_t store_global_boost(struct kobject *kobj, struct attribute *attr,

				  const char *buf, size_t count)

{

	int ret;

	unsigned long val = 0;

	if (!boost_supported)

		return -EINVAL;

	ret = kstrtoul(buf, 10, &val);

	if (ret || (val > 1))

		return -EINVAL;

	if ((val && boost_enabled) || (!val && !boost_enabled))

		return count;

	get_online_cpus();

	boost_set_msrs(val, cpu_online_mask);

	put_online_cpus();

	boost_enabled = val;

	pr_debug("Core Boosting %sabled.\n", val ? "en" : "dis");

	return count;

}

static ssize_t show_global_boost(struct kobject *kobj,

				 struct attribute *attr, char *buf)

{

	return sprintf(buf, "%u\n", boost_enabled);

}

static struct global_attr global_boost = __ATTR(boost, 0644,

						show_global_boost,

						store_global_boost);

static int check_est_cpu(unsigned int cpuid)

{

	free_percpu(acpi_perf_data);

}

static int boost_notify(struct notifier_block *nb, unsigned long action,

		      void *hcpu)

{

	unsigned cpu = (long)hcpu;

	const struct cpumask *cpumask;

	cpumask = get_cpu_mask(cpu);

	/*

	 * Clear the boost-disable bit on the CPU_DOWN path so that

	 * this cpu cannot block the remaining ones from boosting. On

	 * the CPU_UP path we simply keep the boost-disable flag in

	 * sync with the current global state.

	 */

	switch (action) {

	case CPU_UP_PREPARE:

	case CPU_UP_PREPARE_FROZEN:

		boost_set_msrs(boost_enabled, cpumask);

		break;

	case CPU_DOWN_PREPARE:

	case CPU_DOWN_PREPARE_FROZEN:

		boost_set_msrs(1, cpumask);

		break;

	default:

		break;

	}

	return NOTIFY_OK;

}

static struct notifier_block boost_nb = {

	.notifier_call          = boost_notify,

};

/*

 * acpi_cpufreq_early_init - initialize ACPI P-States library

 *

	.attr		= acpi_cpufreq_attr,

};

static void __init acpi_cpufreq_boost_init(void)

{

	if (boot_cpu_has(X86_FEATURE_CPB) || boot_cpu_has(X86_FEATURE_IDA)) {

		msrs = msrs_alloc();

		if (!msrs)

			return;

		boost_supported = true;

		boost_enabled = boost_state(0);

		get_online_cpus();

		/* Force all MSRs to the same value */

		boost_set_msrs(boost_enabled, cpu_online_mask);

		register_cpu_notifier(&boost_nb);

		put_online_cpus();

	} else

		global_boost.attr.mode = 0444;

	/* We create the boost file in any case, though for systems without

	 * hardware support it will be read-only and hardwired to return 0.

	 */

	if (sysfs_create_file(cpufreq_global_kobject, &(global_boost.attr)))

		pr_warn(PFX "could not register global boost sysfs file\n");

	else

		pr_debug("registered global boost sysfs file\n");

}

static void __exit acpi_cpufreq_boost_exit(void)

{

	sysfs_remove_file(cpufreq_global_kobject, &(global_boost.attr));

	if (msrs) {

		unregister_cpu_notifier(&boost_nb);

		msrs_free(msrs);

		msrs = NULL;

	}

}

static int __init acpi_cpufreq_init(void)

{

	int ret;

	ret = cpufreq_register_driver(&acpi_cpufreq_driver);

	if (ret)

		free_acpi_perf_data();

	else

		acpi_cpufreq_boost_init();

	return ret;

}

{

	pr_debug("acpi_cpufreq_exit\n");

	acpi_cpufreq_boost_exit();

	cpufreq_unregister_driver(&acpi_cpufreq_driver);

	free_acpi_perf_data();