Re: [PATCH v7] cpufreq: intel_pstate: Implement passive mode with HWP enabled

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

On Thu, 2020-08-06 at 14:03 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Allow intel_pstate to work in the passive mode with HWP enabled and
> make it set the HWP minimum performance limit (HWP floor) to the
> P-state value given by the target frequency supplied by the cpufreq
> governor, so as to prevent the HWP algorithm and the CPU scheduler
> from working against each other, at least when the schedutil governor
> is in use, and update the intel_pstate documentation accordingly.
> 
> Among other things, this allows utilization clamps to be taken
> into account, at least to a certain extent, when intel_pstate is
> in use and makes it more likely that sufficient capacity for
> deadline tasks will be provided.
> 
> After this change, the resulting behavior of an HWP system with
> intel_pstate in the passive mode should be close to the behavior
> of the analogous non-HWP system with intel_pstate in the passive
> mode, except that in the frequency range below the base frequency
> (ie. the frequency retured by the base_frequency cpufreq attribute
> in sysfs on HWP systems) the HWP algorithm is allowed to make the
> CPU run at a frequency above the floor P-state set by intel_pstate,
> with or without hardware coordination of P-states among CPUs in the
> same package.
> 
> [If P-states of the CPUs in the same package are coordinated at the
>  hardware level, a non-HWP processor may choose a P-state above the
>  target one like a processor with HWP enabled may choose a P-state
>  above the HWP floor, so the HWP behavior is analogous to the non-HWP
>  one in that case.
> 
>  Also note that the HWP floor may not be taken into account by
>  the processor in the range of P-states above the base frequency,
>  referred to as the turbo range, where the processor has a license to
>  choose any P-state, either below or above the HWP floor, just like a
>  non-HWP processor in the case when the target P-state falls into the
>  turbo range.]
> 
> With this change applied, intel_pstate in the passive mode
> assumes complete control over the HWP request MSR and concurrent
> changes of that MSR (eg. via the direct MSR access interface) are
> overridden by it.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

> ---
> 
> Sending the right patch this time, sorry for the confusion.
> 
> This is based on the current mainline.
> 
> v1 -> v2:
>    * Avoid a race condition when updating the HWP request register
> while
>      setting a new EPP value via sysfs.
> 
> v2 -> v3:
>    * Rebase.
> 
> v3 -> v4:
>    * Avoid exposing the hwp_dynamic_boost sysfs switch in the passive
> mode.
> 
> v4 -> v5:
>    * Do not acquire intel_pstate_driver_lock in
>      store_energy_performance_preference(), because it runs under
>      policy->rwsem, so intel_pstate_driver cannot change while it is
> running.
>    * Rearrange the changelog a bit to avoid confusion.
> 
> v5 -> v6:
>    * Fix the problem with the EPP setting via sysfs not working with
> the
>      performance and powersave governors by stopping and restarting
> the
>      governor around the sysfs-based EPP updates in the passive mode.
>    * Because of that, use the epp_cached field just for avoiding the
> above
>      if the new EPP value for the given CPU is the same as the old
> one.
>    * Export cpufreq_start/stop_governor() from the core (for the
> above).
> 
> v6 -> v7:
>    * Cosmetic changes in store_energy_performance_prefernce() to
> reduce the
>      LoC number and make it a bit easier to read.  No intentional
> functional
>      impact.
> 
> ---
>  Documentation/admin-guide/pm/intel_pstate.rst |   89 ++++-----
>  drivers/cpufreq/cpufreq.c                     |    6 
>  drivers/cpufreq/intel_pstate.c                |  245
> +++++++++++++++++++-------
>  include/linux/cpufreq.h                       |    2 
>  4 files changed, 229 insertions(+), 113 deletions(-)
> 
> Index: linux-pm/drivers/cpufreq/intel_pstate.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/intel_pstate.c
> +++ linux-pm/drivers/cpufreq/intel_pstate.c
> @@ -36,6 +36,7 @@
>  #define INTEL_PSTATE_SAMPLING_INTERVAL	(10 * NSEC_PER_MSEC)
>  
>  #define INTEL_CPUFREQ_TRANSITION_LATENCY	20000
> +#define INTEL_CPUFREQ_TRANSITION_DELAY_HWP	5000
>  #define INTEL_CPUFREQ_TRANSITION_DELAY		500
>  
>  #ifdef CONFIG_ACPI
> @@ -220,6 +221,7 @@ struct global_params {
>   *			preference/bias
>   * @epp_saved:		Saved EPP/EPB during system suspend or
> CPU offline
>   *			operation
> + * @epp_cached		Cached HWP energy-performance
> preference value
>   * @hwp_req_cached:	Cached value of the last HWP Request MSR
>   * @hwp_cap_cached:	Cached value of the last HWP Capabilities MSR
>   * @last_io_update:	Last time when IO wake flag was set
> @@ -257,6 +259,7 @@ struct cpudata {
>  	s16 epp_policy;
>  	s16 epp_default;
>  	s16 epp_saved;
> +	s16 epp_cached;
>  	u64 hwp_req_cached;
>  	u64 hwp_cap_cached;
>  	u64 last_io_update;
> @@ -639,6 +642,26 @@ static int intel_pstate_get_energy_pref_
>  	return index;
>  }
>  
> +static int intel_pstate_set_epp(struct cpudata *cpu, u32 epp)
> +{
> +	/*
> +	 * Use the cached HWP Request MSR value, because in the active
> mode the
> +	 * register itself may be updated by
> intel_pstate_hwp_boost_up() or
> +	 * intel_pstate_hwp_boost_down() at any time.
> +	 */
> +	u64 value = READ_ONCE(cpu->hwp_req_cached);
> +
> +	value &= ~GENMASK_ULL(31, 24);
> +	value |= (u64)epp << 24;
> +	/*
> +	 * The only other updater of hwp_req_cached in the active mode,
> +	 * intel_pstate_hwp_set(), is called under the same lock as
> this
> +	 * function, so it cannot run in parallel with the update
> below.
> +	 */
> +	WRITE_ONCE(cpu->hwp_req_cached, value);
> +	return wrmsrl_on_cpu(cpu->cpu, MSR_HWP_REQUEST, value);
> +}
> +
>  static int intel_pstate_set_energy_pref_index(struct cpudata
> *cpu_data,
>  					      int pref_index, bool
> use_raw,
>  					      u32 raw_epp)
> @@ -650,28 +673,12 @@ static int intel_pstate_set_energy_pref_
>  		epp = cpu_data->epp_default;
>  
>  	if (boot_cpu_has(X86_FEATURE_HWP_EPP)) {
> -		/*
> -		 * Use the cached HWP Request MSR value, because the
> register
> -		 * itself may be updated by intel_pstate_hwp_boost_up()
> or
> -		 * intel_pstate_hwp_boost_down() at any time.
> -		 */
> -		u64 value = READ_ONCE(cpu_data->hwp_req_cached);
> -
> -		value &= ~GENMASK_ULL(31, 24);
> -
>  		if (use_raw)
>  			epp = raw_epp;
>  		else if (epp == -EINVAL)
>  			epp = epp_values[pref_index - 1];
>  
> -		value |= (u64)epp << 24;
> -		/*
> -		 * The only other updater of hwp_req_cached in the
> active mode,
> -		 * intel_pstate_hwp_set(), is called under the same
> lock as this
> -		 * function, so it cannot run in parallel with the
> update below.
> -		 */
> -		WRITE_ONCE(cpu_data->hwp_req_cached, value);
> -		ret = wrmsrl_on_cpu(cpu_data->cpu, MSR_HWP_REQUEST,
> value);
> +		ret = intel_pstate_set_epp(cpu_data, epp);
>  	} else {
>  		if (epp == -EINVAL)
>  			epp = (pref_index - 1) << 2;
> @@ -697,10 +704,12 @@ static ssize_t show_energy_performance_a
>  
>  cpufreq_freq_attr_ro(energy_performance_available_preferences);
>  
> +static struct cpufreq_driver intel_pstate;
> +
>  static ssize_t store_energy_performance_preference(
>  		struct cpufreq_policy *policy, const char *buf, size_t
> count)
>  {
> -	struct cpudata *cpu_data = all_cpu_data[policy->cpu];
> +	struct cpudata *cpu = all_cpu_data[policy->cpu];
>  	char str_preference[21];
>  	bool raw = false;
>  	ssize_t ret;
> @@ -725,15 +734,44 @@ static ssize_t store_energy_performance_
>  		raw = true;
>  	}
>  
> +	/*
> +	 * This function runs with the policy R/W semaphore held, which
> +	 * guarantees that the driver pointer will not change while it
> is
> +	 * running.
> +	 */
> +	if (!intel_pstate_driver)
> +		return -EAGAIN;
> +
>  	mutex_lock(&intel_pstate_limits_lock);
>  
> -	ret = intel_pstate_set_energy_pref_index(cpu_data, ret, raw,
> epp);
> -	if (!ret)
> -		ret = count;
> +	if (intel_pstate_driver == &intel_pstate) {
> +		ret = intel_pstate_set_energy_pref_index(cpu, ret, raw,
> epp);
> +	} else {
> +		/*
> +		 * In the passive mode the governor needs to be stopped
> on the
> +		 * target CPU before the EPP update and restarted after
> it,
> +		 * which is super-heavy-weight, so make sure it is
> worth doing
> +		 * upfront.
> +		 */
> +		if (!raw)
> +			epp = ret ? epp_values[ret - 1] : cpu-
> >epp_default;
> +
> +		if (cpu->epp_cached != epp) {
> +			int err;
> +
> +			cpufreq_stop_governor(policy);
> +			ret = intel_pstate_set_epp(cpu, epp);
> +			err = cpufreq_start_governor(policy);
> +			if (!ret) {
> +				cpu->epp_cached = epp;
> +				ret = err;
> +			}
> +		}
> +	}
>  
>  	mutex_unlock(&intel_pstate_limits_lock);
>  
> -	return ret;
> +	return ret ?: count;
>  }
>  
>  static ssize_t show_energy_performance_preference(
> @@ -1145,8 +1183,6 @@ static ssize_t store_no_turbo(struct kob
>  	return count;
>  }
>  
> -static struct cpufreq_driver intel_pstate;
> -
>  static void update_qos_request(enum freq_qos_req_type type)
>  {
>  	int max_state, turbo_max, freq, i, perf_pct;
> @@ -1330,9 +1366,10 @@ static const struct attribute_group inte
>  
>  static const struct x86_cpu_id intel_pstate_cpu_ee_disable_ids[];
>  
> +static struct kobject *intel_pstate_kobject;
> +
>  static void __init intel_pstate_sysfs_expose_params(void)
>  {
> -	struct kobject *intel_pstate_kobject;
>  	int rc;
>  
>  	intel_pstate_kobject = kobject_create_and_add("intel_pstate",
> @@ -1357,17 +1394,31 @@ static void __init intel_pstate_sysfs_ex
>  	rc = sysfs_create_file(intel_pstate_kobject,
> &min_perf_pct.attr);
>  	WARN_ON(rc);
>  
> -	if (hwp_active) {
> -		rc = sysfs_create_file(intel_pstate_kobject,
> -				       &hwp_dynamic_boost.attr);
> -		WARN_ON(rc);
> -	}
> -
>  	if (x86_match_cpu(intel_pstate_cpu_ee_disable_ids)) {
>  		rc = sysfs_create_file(intel_pstate_kobject,
> &energy_efficiency.attr);
>  		WARN_ON(rc);
>  	}
>  }
> +
> +static void intel_pstate_sysfs_expose_hwp_dynamic_boost(void)
> +{
> +	int rc;
> +
> +	if (!hwp_active)
> +		return;
> +
> +	rc = sysfs_create_file(intel_pstate_kobject,
> &hwp_dynamic_boost.attr);
> +	WARN_ON_ONCE(rc);
> +}
> +
> +static void intel_pstate_sysfs_hide_hwp_dynamic_boost(void)
> +{
> +	if (!hwp_active)
> +		return;
> +
> +	sysfs_remove_file(intel_pstate_kobject,
> &hwp_dynamic_boost.attr);
> +}
> +
>  /************************** sysfs end ************************/
>  
>  static void intel_pstate_hwp_enable(struct cpudata *cpudata)
> @@ -2246,7 +2297,10 @@ static int intel_pstate_verify_policy(st
>  
>  static void intel_cpufreq_stop_cpu(struct cpufreq_policy *policy)
>  {
> -	intel_pstate_set_min_pstate(all_cpu_data[policy->cpu]);
> +	if (hwp_active)
> +		intel_pstate_hwp_force_min_perf(policy->cpu);
> +	else
> +		intel_pstate_set_min_pstate(all_cpu_data[policy->cpu]);
>  }
>  
>  static void intel_pstate_stop_cpu(struct cpufreq_policy *policy)
> @@ -2254,12 +2308,10 @@ static void intel_pstate_stop_cpu(struct
>  	pr_debug("CPU %d exiting\n", policy->cpu);
>  
>  	intel_pstate_clear_update_util_hook(policy->cpu);
> -	if (hwp_active) {
> +	if (hwp_active)
>  		intel_pstate_hwp_save_state(policy);
> -		intel_pstate_hwp_force_min_perf(policy->cpu);
> -	} else {
> -		intel_cpufreq_stop_cpu(policy);
> -	}
> +
> +	intel_cpufreq_stop_cpu(policy);
>  }
>  
>  static int intel_pstate_cpu_exit(struct cpufreq_policy *policy)
> @@ -2389,13 +2441,71 @@ static void intel_cpufreq_trace(struct c
>  		fp_toint(cpu->iowait_boost * 100));
>  }
>  
> +static void intel_cpufreq_adjust_hwp(struct cpudata *cpu, u32
> target_pstate,
> +				     bool fast_switch)
> +{
> +	u64 prev = READ_ONCE(cpu->hwp_req_cached), value = prev;
> +
> +	value &= ~HWP_MIN_PERF(~0L);
> +	value |= HWP_MIN_PERF(target_pstate);
> +
> +	/*
> +	 * The entire MSR needs to be updated in order to update the
> HWP min
> +	 * field in it, so opportunistically update the max too if
> needed.
> +	 */
> +	value &= ~HWP_MAX_PERF(~0L);
> +	value |= HWP_MAX_PERF(cpu->max_perf_ratio);
> +
> +	if (value == prev)
> +		return;
> +
> +	WRITE_ONCE(cpu->hwp_req_cached, value);
> +	if (fast_switch)
> +		wrmsrl(MSR_HWP_REQUEST, value);
> +	else
> +		wrmsrl_on_cpu(cpu->cpu, MSR_HWP_REQUEST, value);
> +}
> +
> +static void intel_cpufreq_adjust_perf_ctl(struct cpudata *cpu,
> +					  u32 target_pstate, bool
> fast_switch)
> +{
> +	if (fast_switch)
> +		wrmsrl(MSR_IA32_PERF_CTL,
> +		       pstate_funcs.get_val(cpu, target_pstate));
> +	else
> +		wrmsrl_on_cpu(cpu->cpu, MSR_IA32_PERF_CTL,
> +			      pstate_funcs.get_val(cpu,
> target_pstate));
> +}
> +
> +static int intel_cpufreq_update_pstate(struct cpudata *cpu, int
> target_pstate,
> +				       bool fast_switch)
> +{
> +	int old_pstate = cpu->pstate.current_pstate;
> +
> +	target_pstate = intel_pstate_prepare_request(cpu,
> target_pstate);
> +	if (target_pstate != old_pstate) {
> +		cpu->pstate.current_pstate = target_pstate;
> +		if (hwp_active)
> +			intel_cpufreq_adjust_hwp(cpu, target_pstate,
> +						 fast_switch);
> +		else
> +			intel_cpufreq_adjust_perf_ctl(cpu,
> target_pstate,
> +						      fast_switch);
> +	}
> +
> +	intel_cpufreq_trace(cpu, fast_switch ?
> INTEL_PSTATE_TRACE_FAST_SWITCH :
> +			    INTEL_PSTATE_TRACE_TARGET, old_pstate);
> +
> +	return target_pstate;
> +}
> +
>  static int intel_cpufreq_target(struct cpufreq_policy *policy,
>  				unsigned int target_freq,
>  				unsigned int relation)
>  {
>  	struct cpudata *cpu = all_cpu_data[policy->cpu];
>  	struct cpufreq_freqs freqs;
> -	int target_pstate, old_pstate;
> +	int target_pstate;
>  
>  	update_turbo_state();
>  
> @@ -2403,6 +2513,7 @@ static int intel_cpufreq_target(struct c
>  	freqs.new = target_freq;
>  
>  	cpufreq_freq_transition_begin(policy, &freqs);
> +
>  	switch (relation) {
>  	case CPUFREQ_RELATION_L:
>  		target_pstate = DIV_ROUND_UP(freqs.new, cpu-
> >pstate.scaling);
> @@ -2414,15 +2525,11 @@ static int intel_cpufreq_target(struct c
>  		target_pstate = DIV_ROUND_CLOSEST(freqs.new, cpu-
> >pstate.scaling);
>  		break;
>  	}
> -	target_pstate = intel_pstate_prepare_request(cpu,
> target_pstate);
> -	old_pstate = cpu->pstate.current_pstate;
> -	if (target_pstate != cpu->pstate.current_pstate) {
> -		cpu->pstate.current_pstate = target_pstate;
> -		wrmsrl_on_cpu(policy->cpu, MSR_IA32_PERF_CTL,
> -			      pstate_funcs.get_val(cpu,
> target_pstate));
> -	}
> +
> +	target_pstate = intel_cpufreq_update_pstate(cpu, target_pstate,
> false);
> +
>  	freqs.new = target_pstate * cpu->pstate.scaling;
> -	intel_cpufreq_trace(cpu, INTEL_PSTATE_TRACE_TARGET,
> old_pstate);
> +
>  	cpufreq_freq_transition_end(policy, &freqs, false);
>  
>  	return 0;
> @@ -2432,15 +2539,14 @@ static unsigned int intel_cpufreq_fast_s
>  					      unsigned int target_freq)
>  {
>  	struct cpudata *cpu = all_cpu_data[policy->cpu];
> -	int target_pstate, old_pstate;
> +	int target_pstate;
>  
>  	update_turbo_state();
>  
>  	target_pstate = DIV_ROUND_UP(target_freq, cpu->pstate.scaling);
> -	target_pstate = intel_pstate_prepare_request(cpu,
> target_pstate);
> -	old_pstate = cpu->pstate.current_pstate;
> -	intel_pstate_update_pstate(cpu, target_pstate);
> -	intel_cpufreq_trace(cpu, INTEL_PSTATE_TRACE_FAST_SWITCH,
> old_pstate);
> +
> +	target_pstate = intel_cpufreq_update_pstate(cpu, target_pstate,
> true);
> +
>  	return target_pstate * cpu->pstate.scaling;
>  }
>  
> @@ -2460,7 +2566,6 @@ static int intel_cpufreq_cpu_init(struct
>  		return ret;
>  
>  	policy->cpuinfo.transition_latency =
> INTEL_CPUFREQ_TRANSITION_LATENCY;
> -	policy->transition_delay_us = INTEL_CPUFREQ_TRANSITION_DELAY;
>  	/* This reflects the intel_pstate_get_cpu_pstates() setting. */
>  	policy->cur = policy->cpuinfo.min_freq;
>  
> @@ -2472,10 +2577,18 @@ static int intel_cpufreq_cpu_init(struct
>  
>  	cpu = all_cpu_data[policy->cpu];
>  
> -	if (hwp_active)
> +	if (hwp_active) {
> +		u64 value;
> +
>  		intel_pstate_get_hwp_max(policy->cpu, &turbo_max,
> &max_state);
> -	else
> +		policy->transition_delay_us =
> INTEL_CPUFREQ_TRANSITION_DELAY_HWP;
> +		rdmsrl_on_cpu(cpu->cpu, MSR_HWP_REQUEST, &value);
> +		WRITE_ONCE(cpu->hwp_req_cached, value);
> +		cpu->epp_cached = (value & GENMASK_ULL(31, 24)) >> 24;
> +	} else {
>  		turbo_max = cpu->pstate.turbo_pstate;
> +		policy->transition_delay_us =
> INTEL_CPUFREQ_TRANSITION_DELAY;
> +	}
>  
>  	min_freq = DIV_ROUND_UP(turbo_max * global.min_perf_pct, 100);
>  	min_freq *= cpu->pstate.scaling;
> @@ -2552,6 +2665,10 @@ static void intel_pstate_driver_cleanup(
>  		}
>  	}
>  	put_online_cpus();
> +
> +	if (intel_pstate_driver == &intel_pstate)
> +		intel_pstate_sysfs_hide_hwp_dynamic_boost();
> +
>  	intel_pstate_driver = NULL;
>  }
>  
> @@ -2559,6 +2676,9 @@ static int intel_pstate_register_driver(
>  {
>  	int ret;
>  
> +	if (driver == &intel_pstate)
> +		intel_pstate_sysfs_expose_hwp_dynamic_boost();
> +
>  	memset(&global, 0, sizeof(global));
>  	global.max_perf_pct = 100;
>  
> @@ -2576,9 +2696,6 @@ static int intel_pstate_register_driver(
>  
>  static int intel_pstate_unregister_driver(void)
>  {
> -	if (hwp_active)
> -		return -EBUSY;
> -
>  	cpufreq_unregister_driver(intel_pstate_driver);
>  	intel_pstate_driver_cleanup();
>  
> @@ -2834,7 +2951,10 @@ static int __init intel_pstate_init(void
>  			hwp_active++;
>  			hwp_mode_bdw = id->driver_data;
>  			intel_pstate.attr = hwp_cpufreq_attrs;
> -			default_driver = &intel_pstate;
> +			intel_cpufreq.attr = hwp_cpufreq_attrs;
> +			if (!default_driver)
> +				default_driver = &intel_pstate;
> +
>  			goto hwp_cpu_matched;
>  		}
>  	} else {
> @@ -2905,14 +3025,13 @@ static int __init intel_pstate_setup(cha
>  	if (!str)
>  		return -EINVAL;
>  
> -	if (!strcmp(str, "disable")) {
> +	if (!strcmp(str, "disable"))
>  		no_load = 1;
> -	} else if (!strcmp(str, "active")) {
> +	else if (!strcmp(str, "active"))
>  		default_driver = &intel_pstate;
> -	} else if (!strcmp(str, "passive")) {
> +	else if (!strcmp(str, "passive"))
>  		default_driver = &intel_cpufreq;
> -		no_hwp = 1;
> -	}
> +
>  	if (!strcmp(str, "no_hwp")) {
>  		pr_info("HWP disabled\n");
>  		no_hwp = 1;
> Index: linux-pm/Documentation/admin-guide/pm/intel_pstate.rst
> ===================================================================
> --- linux-pm.orig/Documentation/admin-guide/pm/intel_pstate.rst
> +++ linux-pm/Documentation/admin-guide/pm/intel_pstate.rst
> @@ -54,10 +54,13 @@ registered (see `below <status_attr_>`_)
>  Operation Modes
>  ===============
>  
> -``intel_pstate`` can operate in three different modes: in the active
> mode with
> -or without hardware-managed P-states support and in the passive
> mode.  Which of
> -them will be in effect depends on what kernel command line options
> are used and
> -on the capabilities of the processor.
> +``intel_pstate`` can operate in two different modes, active or
> passive.  In the
> +active mode, it uses its own internal preformance scaling governor
> algorithm or
> +allows the hardware to do preformance scaling by itself, while in
> the passive
> +mode it responds to requests made by a generic ``CPUFreq`` governor
> implementing
> +a certain performance scaling algorithm.  Which of them will be in
> effect
> +depends on what kernel command line options are used and on the
> capabilities of
> +the processor.
>  
>  Active Mode
>  -----------
> @@ -194,10 +197,11 @@ This is the default operation mode of ``
>  hardware-managed P-states (HWP) support.  It is always used if the
>  ``intel_pstate=passive`` argument is passed to the kernel in the
> command line
>  regardless of whether or not the given processor supports
> HWP.  [Note that the
> -``intel_pstate=no_hwp`` setting implies ``intel_pstate=passive`` if
> it is used
> -without ``intel_pstate=active``.]  Like in the active mode without
> HWP support,
> -in this mode ``intel_pstate`` may refuse to work with processors
> that are not
> -recognized by it.
> +``intel_pstate=no_hwp`` setting causes the driver to start in the
> passive mode
> +if it is not combined with ``intel_pstate=active``.]  Like in the
> active mode
> +without HWP support, in this mode ``intel_pstate`` may refuse to
> work with
> +processors that are not recognized by it if HWP is prevented from
> being enabled
> +through the kernel command line.
>  
>  If the driver works in this mode, the ``scaling_driver`` policy
> attribute in
>  ``sysfs`` for all ``CPUFreq`` policies contains the string
> "intel_cpufreq".
> @@ -318,10 +322,9 @@ manuals need to be consulted to get to i
>  
>  For this reason, there is a list of supported processors in
> ``intel_pstate`` and
>  the driver initialization will fail if the detected processor is not
> in that
> -list, unless it supports the `HWP feature <Active Mode_>`_.  [The
> interface to
> -obtain all of the information listed above is the same for all of
> the processors
> -supporting the HWP feature, which is why they all are supported by
> -``intel_pstate``.]
> +list, unless it supports the HWP feature.  [The interface to obtain
> all of the
> +information listed above is the same for all of the processors
> supporting the
> +HWP feature, which is why ``intel_pstate`` works with all of them.]
>  
>  
>  User Space Interface in ``sysfs``
> @@ -425,22 +428,16 @@ argument is passed to the kernel in the
>  	as well as the per-policy ones) are then reset to their default
>  	values, possibly depending on the target operation mode.]
>  
> -	That only is supported in some configurations, though (for
> example, if
> -	the `HWP feature is enabled in the processor <Active Mode With
> HWP_>`_,
> -	the operation mode of the driver cannot be changed), and if it
> is not
> -	supported in the current configuration, writes to this
> attribute will
> -	fail with an appropriate error.
> -
>  ``energy_efficiency``
> -	This attribute is only present on platforms, which have CPUs
> matching
> -	Kaby Lake or Coffee Lake desktop CPU model. By default
> -	energy efficiency optimizations are disabled on these CPU
> models in HWP
> -	mode by this driver. Enabling energy efficiency may limit
> maximum
> -	operating frequency in both HWP and non HWP mode. In non HWP
> mode,
> -	optimizations are done only in the turbo frequency range. In
> HWP mode,
> -	optimizations are done in the entire frequency range. Setting
> this
> -	attribute to "1" enables energy efficiency optimizations and
> setting
> -	to "0" disables energy efficiency optimizations.
> +	This attribute is only present on platforms with CPUs matching
> the Kaby
> +	Lake or Coffee Lake desktop CPU model. By default, energy-
> efficiency
> +	optimizations are disabled on these CPU models if HWP is
> enabled.
> +	Enabling energy-efficiency optimizations may limit maximum
> operating
> +	frequency with or without the HWP feature.  With HWP enabled,
> the
> +	optimizations are done only in the turbo frequency
> range.  Without it,
> +	they are done in the entire available frequency range.  Setting
> this
> +	attribute to "1" enables the energy-efficiency optimizations
> and setting
> +	to "0" disables them.
>  
>  Interpretation of Policy Attributes
>  -----------------------------------
> @@ -484,8 +481,8 @@ Next, the following policy attributes ha
>  	policy for the time interval between the last two invocations
> of the
>  	driver's utilization update callback by the CPU scheduler for
> that CPU.
>  
> -One more policy attribute is present if the `HWP feature is enabled
> in the
> -processor <Active Mode With HWP_>`_:
> +One more policy attribute is present if the HWP feature is enabled
> in the
> +processor:
>  
>  ``base_frequency``
>  	Shows the base frequency of the CPU. Any frequency above this
> will be
> @@ -526,11 +523,11 @@ on the following rules, regardless of th
>  
>   3. The global and per-policy limits can be set independently.
>  
> -If the `HWP feature is enabled in the processor <Active Mode With
> HWP_>`_, the
> -resulting effective values are written into its registers whenever
> the limits
> -change in order to request its internal P-state selection logic to
> always set
> -P-states within these limits.  Otherwise, the limits are taken into
> account by
> -scaling governors (in the `passive mode <Passive Mode_>`_) and by
> the driver
> +In the `active mode with the HWP feature enabled <Active Mode With
> HWP_>`_, the
> +resulting effective values are written into hardware registers
> whenever the
> +limits change in order to request its internal P-state selection
> logic to always
> +set P-states within these limits.  Otherwise, the limits are taken
> into account
> +by scaling governors (in the `passive mode <Passive Mode_>`_) and by
> the driver
>  every time before setting a new P-state for a CPU.
>  
>  Additionally, if the ``intel_pstate=per_cpu_perf_limits`` command
> line argument
> @@ -541,12 +538,11 @@ at all and the only way to set the limit
>  Energy vs Performance Hints
>  ---------------------------
>  
> -If ``intel_pstate`` works in the `active mode with the HWP feature
> enabled
> -<Active Mode With HWP_>`_ in the processor, additional attributes
> are present
> -in every ``CPUFreq`` policy directory in ``sysfs``.  They are
> intended to allow
> -user space to help ``intel_pstate`` to adjust the processor's
> internal P-state
> -selection logic by focusing it on performance or on energy-
> efficiency, or
> -somewhere between the two extremes:
> +If the hardware-managed P-states (HWP) is enabled in the processor,
> additional
> +attributes, intended to allow user space to help ``intel_pstate`` to
> adjust the
> +processor's internal P-state selection logic by focusing it on
> performance or on
> +energy-efficiency, or somewhere between the two extremes, are
> present in every
> +``CPUFreq`` policy directory in ``sysfs``.  They are :
>  
>  ``energy_performance_preference``
>  	Current value of the energy vs performance hint for the given
> policy
> @@ -650,12 +646,14 @@ of them have to be prepended with the ``
>  	Do not register ``intel_pstate`` as the scaling driver even if
> the
>  	processor is supported by it.
>  
> +``active``
> +	Register ``intel_pstate`` in the `active mode <Active Mode_>`_
> to start
> +	with.
> +
>  ``passive``
>  	Register ``intel_pstate`` in the `passive mode <Passive
> Mode_>`_ to
>  	start with.
>  
> -	This option implies the ``no_hwp`` one described below.
> -
>  ``force``
>  	Register ``intel_pstate`` as the scaling driver instead of
>  	``acpi-cpufreq`` even if the latter is preferred on the given
> system.
> @@ -670,13 +668,12 @@ of them have to be prepended with the ``
>  	driver is used instead of ``acpi-cpufreq``.
>  
>  ``no_hwp``
> -	Do not enable the `hardware-managed P-states (HWP) feature
> -	<Active Mode With HWP_>`_ even if it is supported by the
> processor.
> +	Do not enable the hardware-managed P-states (HWP) feature even
> if it is
> +	supported by the processor.
>  
>  ``hwp_only``
>  	Register ``intel_pstate`` as the scaling driver only if the
> -	`hardware-managed P-states (HWP) feature <Active Mode With
> HWP_>`_ is
> -	supported by the processor.
> +	hardware-managed P-states (HWP) feature is supported by the
> processor.
>  
>  ``support_acpi_ppc``
>  	Take ACPI ``_PPC`` performance limits into account.
> Index: linux-pm/drivers/cpufreq/cpufreq.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq.c
> +++ linux-pm/drivers/cpufreq/cpufreq.c
> @@ -73,8 +73,6 @@ static inline bool has_target(void)
>  static unsigned int __cpufreq_get(struct cpufreq_policy *policy);
>  static int cpufreq_init_governor(struct cpufreq_policy *policy);
>  static void cpufreq_exit_governor(struct cpufreq_policy *policy);
> -static int cpufreq_start_governor(struct cpufreq_policy *policy);
> -static void cpufreq_stop_governor(struct cpufreq_policy *policy);
>  static void cpufreq_governor_limits(struct cpufreq_policy *policy);
>  static int cpufreq_set_policy(struct cpufreq_policy *policy,
>  			      struct cpufreq_governor *new_gov,
> @@ -2266,7 +2264,7 @@ static void cpufreq_exit_governor(struct
>  	module_put(policy->governor->owner);
>  }
>  
> -static int cpufreq_start_governor(struct cpufreq_policy *policy)
> +int cpufreq_start_governor(struct cpufreq_policy *policy)
>  {
>  	int ret;
>  
> @@ -2293,7 +2291,7 @@ static int cpufreq_start_governor(struct
>  	return 0;
>  }
>  
> -static void cpufreq_stop_governor(struct cpufreq_policy *policy)
> +void cpufreq_stop_governor(struct cpufreq_policy *policy)
>  {
>  	if (cpufreq_suspended || !policy->governor)
>  		return;
> Index: linux-pm/include/linux/cpufreq.h
> ===================================================================
> --- linux-pm.orig/include/linux/cpufreq.h
> +++ linux-pm/include/linux/cpufreq.h
> @@ -576,6 +576,8 @@ unsigned int cpufreq_driver_resolve_freq
>  unsigned int cpufreq_policy_transition_delay_us(struct
> cpufreq_policy *policy);
>  int cpufreq_register_governor(struct cpufreq_governor *governor);
>  void cpufreq_unregister_governor(struct cpufreq_governor *governor);
> +int cpufreq_start_governor(struct cpufreq_policy *policy);
> +void cpufreq_stop_governor(struct cpufreq_policy *policy);
>  
>  #define cpufreq_governor_init(__governor)			\
>  static int __init __governor##_init(void)			\
> 
> 
>