cpufreq: intel_pstate: Do not use PID-based P-state selection

``powersave``

.............

Without HWP, this P-state selection algorithm generally depends on the

processor model and/or the system profile setting in the ACPI tables and there

are two variants of it.

One of them is used with processors from the Atom line and (regardless of the

processor model) on platforms with the system profile in the ACPI tables set to

"mobile" (laptops mostly), "tablet", "appliance PC", "desktop", or

"workstation".  It is also used with processors supporting the HWP feature if

that feature has not been enabled (that is, with the ``intel_pstate=no_hwp``

argument in the kernel command line).  It is similar to the algorithm

Without HWP, this P-state selection algorithm is similar to the algorithm

implemented by the generic ``schedutil`` scaling governor except that the

utilization metric used by it is based on numbers coming from feedback

registers of the CPU.  It generally selects P-states proportional to the

current CPU utilization, so it is referred to as the "proportional" algorithm.

The second variant of the ``powersave`` P-state selection algorithm, used in all

of the other cases (generally, on processors from the Core line, so it is

referred to as the "Core" algorithm), is based on the values read from the APERF

and MPERF feedback registers and the previously requested target P-state.

It does not really take CPU utilization into account explicitly, but as a rule

it causes the CPU P-state to ramp up very quickly in response to increased

utilization which is generally desirable in server environments.

Regardless of the variant, this algorithm is run by the driver's utilization

update callback for the given CPU when it is invoked by the CPU scheduler, but

not more often than every 10 ms (that can be tweaked via ``debugfs`` in `this

particular case <Tuning Interface in debugfs_>`_).  Like in the ``performance``

case, the hardware configuration is not touched if the new P-state turns out to

be the same as the current one.

current CPU utilization.

This algorithm is run by the driver's utilization update callback for the

given CPU when it is invoked by the CPU scheduler, but not more often than

every 10 ms.  Like in the ``performance`` case, the hardware configuration

is not touched if the new P-state turns out to be the same as the current

one.

This is the default P-state selection algorithm if the

:c:macro:`CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE` kernel configuration option

      gnome-shell-3409  [001] ..s.  2537.650850: intel_pstate_set_pstate <-intel_pstate_timer_func

           <idle>-0     [000] ..s.  2537.654843: intel_pstate_set_pstate <-intel_pstate_timer_func

Tuning Interface in ``debugfs``

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

The ``powersave`` algorithm provided by ``intel_pstate`` for `the Core line of

processors in the active mode <powersave_>`_ is based on a `PID controller`_

whose parameters were chosen to address a number of different use cases at the

same time.  However, it still is possible to fine-tune it to a specific workload

and the ``debugfs`` interface under ``/sys/kernel/debug/pstate_snb/`` is

provided for this purpose.  [Note that the ``pstate_snb`` directory will be

present only if the specific P-state selection algorithm matching the interface

in it actually is in use.]

The following files present in that directory can be used to modify the PID

controller parameters at run time:

| ``deadband``

| ``d_gain_pct``

| ``i_gain_pct``

| ``p_gain_pct``

| ``sample_rate_ms``

| ``setpoint``

Note, however, that achieving desirable results this way generally requires

expert-level understanding of the power vs performance tradeoff, so extra care

is recommended when attempting to do that.

.. _LCEU2015: http://events.linuxfoundation.org/sites/events/files/slides/LinuxConEurope_2015.pdf

.. _SDM: http://www.intel.com/content/www/us/en/architecture-and-technology/64-ia-32-architectures-software-developer-system-programming-manual-325384.html

.. _ACPI specification: http://www.uefi.org/sites/default/files/resources/ACPI_6_1.pdf

.. _PID controller: https://en.wikipedia.org/wiki/PID_controller

	int32_t ratio;

};

/**

 * struct _pid -	Stores PID data

 * @setpoint:		Target set point for busyness or performance

 * @integral:		Storage for accumulated error values

 * @p_gain:		PID proportional gain

 * @i_gain:		PID integral gain

 * @d_gain:		PID derivative gain

 * @deadband:		PID deadband

 * @last_err:		Last error storage for integral part of PID calculation

 *

 * Stores PID coefficients and last error for PID controller.

 */

struct _pid {

	int setpoint;

	int32_t integral;

	int32_t p_gain;

	int32_t i_gain;

	int32_t d_gain;

	int deadband;

	int32_t last_err;

};

/**

 * struct global_params - Global parameters, mostly tunable via sysfs.

 * @no_turbo:		Whether or not to use turbo P-states.

 * @last_update:	Time of the last update.

 * @pstate:		Stores P state limits for this CPU

 * @vid:		Stores VID limits for this CPU

 * @pid:		Stores PID parameters for this CPU

 * @last_sample_time:	Last Sample time

 * @aperf_mperf_shift:	Number of clock cycles after aperf, merf is incremented

 *			This shift is a multiplier to mperf delta to

	struct pstate_data pstate;

	struct vid_data vid;

	struct _pid pid;

	u64	last_update;

	u64	last_sample_time;

static struct cpudata **all_cpu_data;

/**

 * struct pstate_adjust_policy - Stores static PID configuration data

 * @sample_rate_ms:	PID calculation sample rate in ms

 * @sample_rate_ns:	Sample rate calculation in ns

 * @deadband:		PID deadband

 * @setpoint:		PID Setpoint

 * @p_gain_pct:		PID proportional gain

 * @i_gain_pct:		PID integral gain

 * @d_gain_pct:		PID derivative gain

 *

 * Stores per CPU model static PID configuration data.

 */

struct pstate_adjust_policy {

	int sample_rate_ms;

	s64 sample_rate_ns;

	int deadband;

	int setpoint;

	int p_gain_pct;

	int d_gain_pct;

	int i_gain_pct;

};

/**

 * struct pstate_funcs - Per CPU model specific callbacks

 * @get_max:		Callback to get maximum non turbo effective P state

};

static struct pstate_funcs pstate_funcs __read_mostly;

static struct pstate_adjust_policy pid_params __read_mostly = {

	.sample_rate_ms = 10,

	.sample_rate_ns = 10 * NSEC_PER_MSEC,

	.deadband = 0,

	.setpoint = 97,

	.p_gain_pct = 20,

	.d_gain_pct = 0,

	.i_gain_pct = 0,

};

static int hwp_active __read_mostly;

static bool per_cpu_limits __read_mostly;

}

#endif

static signed int pid_calc(struct _pid *pid, int32_t busy)

{

	signed int result;

	int32_t pterm, dterm, fp_error;

	int32_t integral_limit;

	fp_error = pid->setpoint - busy;

	if (abs(fp_error) <= pid->deadband)

		return 0;

	pterm = mul_fp(pid->p_gain, fp_error);

	pid->integral += fp_error;

	/*

	 * We limit the integral here so that it will never

	 * get higher than 30.  This prevents it from becoming

	 * too large an input over long periods of time and allows

	 * it to get factored out sooner.

	 *

	 * The value of 30 was chosen through experimentation.

	 */

	integral_limit = int_tofp(30);

	if (pid->integral > integral_limit)

		pid->integral = integral_limit;

	if (pid->integral < -integral_limit)

		pid->integral = -integral_limit;

	dterm = mul_fp(pid->d_gain, fp_error - pid->last_err);

	pid->last_err = fp_error;

	result = pterm + mul_fp(pid->integral, pid->i_gain) + dterm;

	result = result + (1 << (FRAC_BITS-1));

	return (signed int)fp_toint(result);

}

static inline void intel_pstate_pid_reset(struct cpudata *cpu)

{

	struct _pid *pid = &cpu->pid;

	pid->p_gain = percent_fp(pid_params.p_gain_pct);

	pid->d_gain = percent_fp(pid_params.d_gain_pct);

	pid->i_gain = percent_fp(pid_params.i_gain_pct);

	pid->setpoint = int_tofp(pid_params.setpoint);

	pid->last_err  = pid->setpoint - int_tofp(100);

	pid->deadband  = int_tofp(pid_params.deadband);

	pid->integral  = 0;

}

static inline void update_turbo_state(void)

{

	u64 misc_en;

		cpufreq_update_policy(cpu);

}

/************************** debugfs begin ************************/

static int pid_param_set(void *data, u64 val)

{

	unsigned int cpu;

	*(u32 *)data = val;

	pid_params.sample_rate_ns = pid_params.sample_rate_ms * NSEC_PER_MSEC;

	for_each_possible_cpu(cpu)

		if (all_cpu_data[cpu])

			intel_pstate_pid_reset(all_cpu_data[cpu]);

	return 0;

}

static int pid_param_get(void *data, u64 *val)

{

	*val = *(u32 *)data;

	return 0;

}

DEFINE_SIMPLE_ATTRIBUTE(fops_pid_param, pid_param_get, pid_param_set, "%llu\n");

static struct dentry *debugfs_parent;

struct pid_param {

	char *name;

	void *value;

	struct dentry *dentry;

};

static struct pid_param pid_files[] = {

	{"sample_rate_ms", &pid_params.sample_rate_ms, },

	{"d_gain_pct", &pid_params.d_gain_pct, },

	{"i_gain_pct", &pid_params.i_gain_pct, },

	{"deadband", &pid_params.deadband, },

	{"setpoint", &pid_params.setpoint, },

	{"p_gain_pct", &pid_params.p_gain_pct, },

	{NULL, NULL, }

};

static void intel_pstate_debug_expose_params(void)

{

	int i;

	debugfs_parent = debugfs_create_dir("pstate_snb", NULL);

	if (IS_ERR_OR_NULL(debugfs_parent))

		return;

	for (i = 0; pid_files[i].name; i++) {

		struct dentry *dentry;

		dentry = debugfs_create_file(pid_files[i].name, 0660,

					     debugfs_parent, pid_files[i].value,

					     &fops_pid_param);

		if (!IS_ERR(dentry))

			pid_files[i].dentry = dentry;

	}

}

static void intel_pstate_debug_hide_params(void)

{

	int i;

	if (IS_ERR_OR_NULL(debugfs_parent))

		return;

	for (i = 0; pid_files[i].name; i++) {

		debugfs_remove(pid_files[i].dentry);

		pid_files[i].dentry = NULL;

	}

	debugfs_remove(debugfs_parent);

	debugfs_parent = NULL;

}

/************************** debugfs end ************************/

/************************** sysfs begin ************************/

#define show_one(file_name, object)					\

	static ssize_t show_##file_name					\

	return target;

}

static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)

{

	int32_t perf_scaled, max_pstate, current_pstate, sample_ratio;

	u64 duration_ns;

	/*

	 * perf_scaled is the ratio of the average P-state during the last

	 * sampling period to the P-state requested last time (in percent).

	 *

	 * That measures the system's response to the previous P-state

	 * selection.

	 */

	max_pstate = cpu->pstate.max_pstate_physical;

	current_pstate = cpu->pstate.current_pstate;

	perf_scaled = mul_ext_fp(cpu->sample.core_avg_perf,

			       div_fp(100 * max_pstate, current_pstate));

	/*

	 * Since our utilization update callback will not run unless we are

	 * in C0, check if the actual elapsed time is significantly greater (3x)

	 * than our sample interval.  If it is, then we were idle for a long

	 * enough period of time to adjust our performance metric.

	 */

	duration_ns = cpu->sample.time - cpu->last_sample_time;

	if ((s64)duration_ns > pid_params.sample_rate_ns * 3) {

		sample_ratio = div_fp(pid_params.sample_rate_ns, duration_ns);

		perf_scaled = mul_fp(perf_scaled, sample_ratio);

	} else {

		sample_ratio = div_fp(100 * (cpu->sample.mperf << cpu->aperf_mperf_shift),

				      cpu->sample.tsc);

		if (sample_ratio < int_tofp(1))

			perf_scaled = 0;

	}

	cpu->sample.busy_scaled = perf_scaled;

	return cpu->pstate.current_pstate - pid_calc(&cpu->pid, perf_scaled);

}

static int intel_pstate_prepare_request(struct cpudata *cpu, int pstate)

{

	int max_pstate = intel_pstate_get_base_pstate(cpu);

		fp_toint(cpu->iowait_boost * 100));

}

static void intel_pstate_update_util_pid(struct update_util_data *data,

					 u64 time, unsigned int flags)

{

	struct cpudata *cpu = container_of(data, struct cpudata, update_util);

	u64 delta_ns = time - cpu->sample.time;

	if ((s64)delta_ns < pid_params.sample_rate_ns)

		return;

	if (intel_pstate_sample(cpu, time)) {

		int target_pstate;

		target_pstate = get_target_pstate_use_performance(cpu);

		intel_pstate_adjust_pstate(cpu, target_pstate);

	}

}

static void intel_pstate_update_util(struct update_util_data *data, u64 time,

				     unsigned int flags)

{

	.get_turbo = core_get_turbo_pstate,

	.get_scaling = core_get_scaling,

	.get_val = core_get_val,

	.update_util = intel_pstate_update_util_pid,

	.update_util = intel_pstate_update_util,

};

static const struct pstate_funcs silvermont_funcs = {

	.get_aperf_mperf_shift = knl_get_aperf_mperf_shift,

	.get_scaling = core_get_scaling,

	.get_val = core_get_val,

	.update_util = intel_pstate_update_util_pid,

	.update_util = intel_pstate_update_util,

};

static const struct pstate_funcs bxt_funcs = {

	{}

};

static bool pid_in_use(void);

static int intel_pstate_init_cpu(unsigned int cpunum)

{

	struct cpudata *cpu;

			intel_pstate_disable_ee(cpunum);

		intel_pstate_hwp_enable(cpu);

	} else if (pid_in_use()) {

		intel_pstate_pid_reset(cpu);

	}

	intel_pstate_get_cpu_pstates(cpu);

static struct cpufreq_driver *default_driver = &intel_pstate;

static bool pid_in_use(void)

{

	return intel_pstate_driver == &intel_pstate &&

		pstate_funcs.update_util == intel_pstate_update_util_pid;

}

static void intel_pstate_driver_cleanup(void)

{

	unsigned int cpu;

	global.min_perf_pct = min_perf_pct_min();

	if (pid_in_use())

		intel_pstate_debug_expose_params();

	return 0;

}

	if (hwp_active)

		return -EBUSY;

	if (pid_in_use())

		intel_pstate_debug_hide_params();

	cpufreq_unregister_driver(intel_pstate_driver);

	intel_pstate_driver_cleanup();

	return 0;

}

#ifdef CONFIG_ACPI

static void intel_pstate_use_acpi_profile(void)

{

	switch (acpi_gbl_FADT.preferred_profile) {

	case PM_MOBILE:

	case PM_TABLET:

	case PM_APPLIANCE_PC:

	case PM_DESKTOP:

	case PM_WORKSTATION:

		pstate_funcs.update_util = intel_pstate_update_util;

	}

}

#else

static void intel_pstate_use_acpi_profile(void)

{

}

#endif

static void __init copy_cpu_funcs(struct pstate_funcs *funcs)

{

	pstate_funcs.get_max   = funcs->get_max;

	pstate_funcs.get_vid   = funcs->get_vid;

	pstate_funcs.update_util = funcs->update_util;

	pstate_funcs.get_aperf_mperf_shift = funcs->get_aperf_mperf_shift;

	intel_pstate_use_acpi_profile();

}

#ifdef CONFIG_ACPI