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cpufreq_governor.c

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  • cpufreq_governor.c 16.39 KiB
    /*
     * drivers/cpufreq/cpufreq_governor.c
     *
     * CPUFREQ governors common code
     *
     * Copyright	(C) 2001 Russell King
     *		(C) 2003 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>.
     *		(C) 2003 Jun Nakajima <jun.nakajima@intel.com>
     *		(C) 2009 Alexander Clouter <alex@digriz.org.uk>
     *		(c) 2012 Viresh Kumar <viresh.kumar@linaro.org>
     *
     * 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.
     */
    
    #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
    
    #include <linux/export.h>
    #include <linux/kernel_stat.h>
    #include <linux/sched.h>
    #include <linux/slab.h>
    
    #include "cpufreq_governor.h"
    
    static DEFINE_PER_CPU(struct cpu_dbs_info, cpu_dbs);
    
    static DEFINE_MUTEX(gov_dbs_data_mutex);
    
    /* Common sysfs tunables */
    /**
     * store_sampling_rate - update sampling rate effective immediately if needed.
     *
     * If new rate is smaller than the old, simply updating
     * dbs.sampling_rate might not be appropriate. For example, if the
     * original sampling_rate was 1 second and the requested new sampling rate is 10
     * ms because the user needs immediate reaction from ondemand governor, but not
     * sure if higher frequency will be required or not, then, the governor may
     * change the sampling rate too late; up to 1 second later. Thus, if we are
     * reducing the sampling rate, we need to make the new value effective
     * immediately.
     *
     * This must be called with dbs_data->mutex held, otherwise traversing
     * policy_dbs_list isn't safe.
     */
    ssize_t store_sampling_rate(struct gov_attr_set *attr_set, const char *buf,
    			    size_t count)
    {
    	struct dbs_data *dbs_data = to_dbs_data(attr_set);
    	struct policy_dbs_info *policy_dbs;
    	unsigned int rate;
    	int ret;
    	ret = sscanf(buf, "%u", &rate);
    	if (ret != 1)
    		return -EINVAL;
    
    	dbs_data->sampling_rate = max(rate, dbs_data->min_sampling_rate);
    
    	/*
    	 * We are operating under dbs_data->mutex and so the list and its
    	 * entries can't be freed concurrently.
    	 */
    	list_for_each_entry(policy_dbs, &attr_set->policy_list, list) {
    		mutex_lock(&policy_dbs->update_mutex);
    		/*
    		 * On 32-bit architectures this may race with the
    		 * sample_delay_ns read in dbs_update_util_handler(), but that
    		 * really doesn't matter.  If the read returns a value that's
    		 * too big, the sample will be skipped, but the next invocation
    		 * of dbs_update_util_handler() (when the update has been
    		 * completed) will take a sample.
    		 *
    		 * If this runs in parallel with dbs_work_handler(), we may end
    		 * up overwriting the sample_delay_ns value that it has just
    		 * written, but it will be corrected next time a sample is
    		 * taken, so it shouldn't be significant.
    		 */
    		gov_update_sample_delay(policy_dbs, 0);
    		mutex_unlock(&policy_dbs->update_mutex);
    	}
    
    	return count;
    }
    EXPORT_SYMBOL_GPL(store_sampling_rate);
    
    /**
     * gov_update_cpu_data - Update CPU load data.
     * @dbs_data: Top-level governor data pointer.
     *
     * Update CPU load data for all CPUs in the domain governed by @dbs_data
     * (that may be a single policy or a bunch of them if governor tunables are
     * system-wide).
     *
     * Call under the @dbs_data mutex.
     */
    void gov_update_cpu_data(struct dbs_data *dbs_data)
    {
    	struct policy_dbs_info *policy_dbs;
    
    	list_for_each_entry(policy_dbs, &dbs_data->attr_set.policy_list, list) {
    		unsigned int j;
    
    		for_each_cpu(j, policy_dbs->policy->cpus) {
    			struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
    
    			j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_update_time,
    								  dbs_data->io_is_busy);
    			if (dbs_data->ignore_nice_load)
    				j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
    		}
    	}
    }
    EXPORT_SYMBOL_GPL(gov_update_cpu_data);
    
    unsigned int dbs_update(struct cpufreq_policy *policy)
    {
    	struct policy_dbs_info *policy_dbs = policy->governor_data;
    	struct dbs_data *dbs_data = policy_dbs->dbs_data;
    	unsigned int ignore_nice = dbs_data->ignore_nice_load;
    	unsigned int max_load = 0, idle_periods = UINT_MAX;
    	unsigned int sampling_rate, io_busy, j;
    
    	/*
    	 * Sometimes governors may use an additional multiplier to increase
    	 * sample delays temporarily.  Apply that multiplier to sampling_rate
    	 * so as to keep the wake-up-from-idle detection logic a bit
    	 * conservative.
    	 */
    	sampling_rate = dbs_data->sampling_rate * policy_dbs->rate_mult;
    	/*
    	 * For the purpose of ondemand, waiting for disk IO is an indication
    	 * that you're performance critical, and not that the system is actually
    	 * idle, so do not add the iowait time to the CPU idle time then.
    	 */
    	io_busy = dbs_data->io_is_busy;
    
    	/* Get Absolute Load */
    	for_each_cpu(j, policy->cpus) {
    		struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
    		u64 update_time, cur_idle_time;
    		unsigned int idle_time, time_elapsed;
    		unsigned int load;
    
    		cur_idle_time = get_cpu_idle_time(j, &update_time, io_busy);
    
    		time_elapsed = update_time - j_cdbs->prev_update_time;
    		j_cdbs->prev_update_time = update_time;
    
    		idle_time = cur_idle_time - j_cdbs->prev_cpu_idle;
    		j_cdbs->prev_cpu_idle = cur_idle_time;
    
    		if (ignore_nice) {
    			u64 cur_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
    
    			idle_time += cputime_to_usecs(cur_nice - j_cdbs->prev_cpu_nice);
    			j_cdbs->prev_cpu_nice = cur_nice;
    		}
    
    		if (unlikely(!time_elapsed)) {
    			/*
    			 * That can only happen when this function is called
    			 * twice in a row with a very short interval between the
    			 * calls, so the previous load value can be used then.
    			 */
    			load = j_cdbs->prev_load;
    		} else if (unlikely(time_elapsed > 2 * sampling_rate &&
    				    j_cdbs->prev_load)) {
    			/*
    			 * If the CPU had gone completely idle and a task has
    			 * just woken up on this CPU now, it would be unfair to
    			 * calculate 'load' the usual way for this elapsed
    			 * time-window, because it would show near-zero load,
    			 * irrespective of how CPU intensive that task actually
    			 * was. This is undesirable for latency-sensitive bursty
    			 * workloads.
    			 *
    			 * To avoid this, reuse the 'load' from the previous
    			 * time-window and give this task a chance to start with
    			 * a reasonably high CPU frequency. However, that
    			 * shouldn't be over-done, lest we get stuck at a high
    			 * load (high frequency) for too long, even when the
    			 * current system load has actually dropped down, so
    			 * clear prev_load to guarantee that the load will be
    			 * computed again next time.
    			 *
    			 * Detecting this situation is easy: the governor's
    			 * utilization update handler would not have run during
    			 * CPU-idle periods.  Hence, an unusually large
    			 * 'time_elapsed' (as compared to the sampling rate)
    			 * indicates this scenario.
    			 */
    			load = j_cdbs->prev_load;
    			j_cdbs->prev_load = 0;
    		} else {
    			if (time_elapsed >= idle_time) {
    				load = 100 * (time_elapsed - idle_time) / time_elapsed;
    			} else {
    				/*
    				 * That can happen if idle_time is returned by
    				 * get_cpu_idle_time_jiffy().  In that case
    				 * idle_time is roughly equal to the difference
    				 * between time_elapsed and "busy time" obtained
    				 * from CPU statistics.  Then, the "busy time"
    				 * can end up being greater than time_elapsed
    				 * (for example, if jiffies_64 and the CPU
    				 * statistics are updated by different CPUs),
    				 * so idle_time may in fact be negative.  That
    				 * means, though, that the CPU was busy all
    				 * the time (on the rough average) during the
    				 * last sampling interval and 100 can be
    				 * returned as the load.
    				 */
    				load = (int)idle_time < 0 ? 100 : 0;
    			}
    			j_cdbs->prev_load = load;
    		}
    
    		if (time_elapsed > 2 * sampling_rate) {
    			unsigned int periods = time_elapsed / sampling_rate;
    
    			if (periods < idle_periods)
    				idle_periods = periods;
    		}
    
    		if (load > max_load)
    			max_load = load;
    	}
    
    	policy_dbs->idle_periods = idle_periods;
    
    	return max_load;
    }
    EXPORT_SYMBOL_GPL(dbs_update);
    
    static void dbs_work_handler(struct work_struct *work)
    {
    	struct policy_dbs_info *policy_dbs;
    	struct cpufreq_policy *policy;
    	struct dbs_governor *gov;
    
    	policy_dbs = container_of(work, struct policy_dbs_info, work);
    	policy = policy_dbs->policy;
    	gov = dbs_governor_of(policy);
    
    	/*
    	 * Make sure cpufreq_governor_limits() isn't evaluating load or the
    	 * ondemand governor isn't updating the sampling rate in parallel.
    	 */
    	mutex_lock(&policy_dbs->update_mutex);
    	gov_update_sample_delay(policy_dbs, gov->gov_dbs_update(policy));
    	mutex_unlock(&policy_dbs->update_mutex);
    
    	/* Allow the utilization update handler to queue up more work. */
    	atomic_set(&policy_dbs->work_count, 0);
    	/*
    	 * If the update below is reordered with respect to the sample delay
    	 * modification, the utilization update handler may end up using a stale
    	 * sample delay value.
    	 */
    	smp_wmb();
    	policy_dbs->work_in_progress = false;
    }
    
    static void dbs_irq_work(struct irq_work *irq_work)
    {
    	struct policy_dbs_info *policy_dbs;
    
    	policy_dbs = container_of(irq_work, struct policy_dbs_info, irq_work);
    	schedule_work_on(smp_processor_id(), &policy_dbs->work);
    }
    
    static void dbs_update_util_handler(struct update_util_data *data, u64 time,
    				    unsigned int flags)
    {
    	struct cpu_dbs_info *cdbs = container_of(data, struct cpu_dbs_info, update_util);
    	struct policy_dbs_info *policy_dbs = cdbs->policy_dbs;
    	u64 delta_ns, lst;
    
    	/*
    	 * The work may not be allowed to be queued up right now.
    	 * Possible reasons:
    	 * - Work has already been queued up or is in progress.
    	 * - It is too early (too little time from the previous sample).
    	 */
    	if (policy_dbs->work_in_progress)
    		return;
    
    	/*
    	 * If the reads below are reordered before the check above, the value
    	 * of sample_delay_ns used in the computation may be stale.
    	 */
    	smp_rmb();
    	lst = READ_ONCE(policy_dbs->last_sample_time);
    	delta_ns = time - lst;
    	if ((s64)delta_ns < policy_dbs->sample_delay_ns)
    		return;
    
    	/*
    	 * If the policy is not shared, the irq_work may be queued up right away
    	 * at this point.  Otherwise, we need to ensure that only one of the
    	 * CPUs sharing the policy will do that.
    	 */
    	if (policy_dbs->is_shared) {
    		if (!atomic_add_unless(&policy_dbs->work_count, 1, 1))
    			return;
    
    		/*
    		 * If another CPU updated last_sample_time in the meantime, we
    		 * shouldn't be here, so clear the work counter and bail out.
    		 */
    		if (unlikely(lst != READ_ONCE(policy_dbs->last_sample_time))) {
    			atomic_set(&policy_dbs->work_count, 0);
    			return;
    		}
    	}
    
    	policy_dbs->last_sample_time = time;
    	policy_dbs->work_in_progress = true;
    	irq_work_queue(&policy_dbs->irq_work);
    }
    
    static void gov_set_update_util(struct policy_dbs_info *policy_dbs,
    				unsigned int delay_us)
    {
    	struct cpufreq_policy *policy = policy_dbs->policy;
    	int cpu;
    
    	gov_update_sample_delay(policy_dbs, delay_us);
    	policy_dbs->last_sample_time = 0;
    
    	for_each_cpu(cpu, policy->cpus) {
    		struct cpu_dbs_info *cdbs = &per_cpu(cpu_dbs, cpu);
    
    		cpufreq_add_update_util_hook(cpu, &cdbs->update_util,
    					     dbs_update_util_handler);
    	}
    }
    
    static inline void gov_clear_update_util(struct cpufreq_policy *policy)
    {
    	int i;
    
    	for_each_cpu(i, policy->cpus)
    		cpufreq_remove_update_util_hook(i);
    
    	synchronize_sched();
    }
    
    static struct policy_dbs_info *alloc_policy_dbs_info(struct cpufreq_policy *policy,
    						     struct dbs_governor *gov)
    {
    	struct policy_dbs_info *policy_dbs;
    	int j;
    
    	/* Allocate memory for per-policy governor data. */
    	policy_dbs = gov->alloc();
    	if (!policy_dbs)
    		return NULL;
    
    	policy_dbs->policy = policy;
    	mutex_init(&policy_dbs->update_mutex);
    	atomic_set(&policy_dbs->work_count, 0);
    	init_irq_work(&policy_dbs->irq_work, dbs_irq_work);
    	INIT_WORK(&policy_dbs->work, dbs_work_handler);
    
    	/* Set policy_dbs for all CPUs, online+offline */
    	for_each_cpu(j, policy->related_cpus) {
    		struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
    
    		j_cdbs->policy_dbs = policy_dbs;
    	}
    	return policy_dbs;
    }
    
    static void free_policy_dbs_info(struct policy_dbs_info *policy_dbs,
    				 struct dbs_governor *gov)
    {
    	int j;
    
    	mutex_destroy(&policy_dbs->update_mutex);
    
    	for_each_cpu(j, policy_dbs->policy->related_cpus) {
    		struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
    
    		j_cdbs->policy_dbs = NULL;
    		j_cdbs->update_util.func = NULL;
    	}
    	gov->free(policy_dbs);
    }
    
    int cpufreq_dbs_governor_init(struct cpufreq_policy *policy)
    {
    	struct dbs_governor *gov = dbs_governor_of(policy);
    	struct dbs_data *dbs_data;
    	struct policy_dbs_info *policy_dbs;
    	unsigned int latency;
    	int ret = 0;
    
    	/* State should be equivalent to EXIT */
    	if (policy->governor_data)
    		return -EBUSY;
    
    	policy_dbs = alloc_policy_dbs_info(policy, gov);
    	if (!policy_dbs)
    		return -ENOMEM;
    
    	/* Protect gov->gdbs_data against concurrent updates. */
    	mutex_lock(&gov_dbs_data_mutex);
    
    	dbs_data = gov->gdbs_data;
    	if (dbs_data) {
    		if (WARN_ON(have_governor_per_policy())) {
    			ret = -EINVAL;
    			goto free_policy_dbs_info;
    		}
    		policy_dbs->dbs_data = dbs_data;
    		policy->governor_data = policy_dbs;
    
    		gov_attr_set_get(&dbs_data->attr_set, &policy_dbs->list);
    		goto out;
    	}
    
    	dbs_data = kzalloc(sizeof(*dbs_data), GFP_KERNEL);
    	if (!dbs_data) {
    		ret = -ENOMEM;
    		goto free_policy_dbs_info;
    	}
    
    	gov_attr_set_init(&dbs_data->attr_set, &policy_dbs->list);
    
    	ret = gov->init(dbs_data);
    	if (ret)
    		goto free_policy_dbs_info;
    
    	/* policy latency is in ns. Convert it to us first */
    	latency = policy->cpuinfo.transition_latency / 1000;
    	if (latency == 0)
    		latency = 1;
    
    	/* Bring kernel and HW constraints together */
    	dbs_data->min_sampling_rate = max(dbs_data->min_sampling_rate,
    					  MIN_LATENCY_MULTIPLIER * latency);
    	dbs_data->sampling_rate = max(dbs_data->min_sampling_rate,
    				      LATENCY_MULTIPLIER * latency);
    
    	if (!have_governor_per_policy())
    		gov->gdbs_data = dbs_data;
    
    	policy_dbs->dbs_data = dbs_data;
    	policy->governor_data = policy_dbs;
    
    	gov->kobj_type.sysfs_ops = &governor_sysfs_ops;
    	ret = kobject_init_and_add(&dbs_data->attr_set.kobj, &gov->kobj_type,
    				   get_governor_parent_kobj(policy),
    				   "%s", gov->gov.name);
    	if (!ret)
    		goto out;
    
    	/* Failure, so roll back. */
    	pr_err("initialization failed (dbs_data kobject init error %d)\n", ret);
    
    	policy->governor_data = NULL;
    
    	if (!have_governor_per_policy())
    		gov->gdbs_data = NULL;
    	gov->exit(dbs_data);
    	kfree(dbs_data);
    
    free_policy_dbs_info:
    	free_policy_dbs_info(policy_dbs, gov);
    
    out:
    	mutex_unlock(&gov_dbs_data_mutex);
    	return ret;
    }
    EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_init);
    
    void cpufreq_dbs_governor_exit(struct cpufreq_policy *policy)
    {
    	struct dbs_governor *gov = dbs_governor_of(policy);
    	struct policy_dbs_info *policy_dbs = policy->governor_data;
    	struct dbs_data *dbs_data = policy_dbs->dbs_data;
    	unsigned int count;
    
    	/* Protect gov->gdbs_data against concurrent updates. */
    	mutex_lock(&gov_dbs_data_mutex);
    
    	count = gov_attr_set_put(&dbs_data->attr_set, &policy_dbs->list);
    
    	policy->governor_data = NULL;
    
    	if (!count) {
    		if (!have_governor_per_policy())
    			gov->gdbs_data = NULL;
    
    		gov->exit(dbs_data);
    		kfree(dbs_data);
    	}
    
    	free_policy_dbs_info(policy_dbs, gov);
    
    	mutex_unlock(&gov_dbs_data_mutex);
    }
    EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_exit);
    
    int cpufreq_dbs_governor_start(struct cpufreq_policy *policy)
    {
    	struct dbs_governor *gov = dbs_governor_of(policy);
    	struct policy_dbs_info *policy_dbs = policy->governor_data;
    	struct dbs_data *dbs_data = policy_dbs->dbs_data;
    	unsigned int sampling_rate, ignore_nice, j;
    	unsigned int io_busy;
    
    	if (!policy->cur)
    		return -EINVAL;
    
    	policy_dbs->is_shared = policy_is_shared(policy);
    	policy_dbs->rate_mult = 1;
    
    	sampling_rate = dbs_data->sampling_rate;
    	ignore_nice = dbs_data->ignore_nice_load;
    	io_busy = dbs_data->io_is_busy;
    
    	for_each_cpu(j, policy->cpus) {
    		struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
    
    		j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_update_time, io_busy);
    		/*
    		 * Make the first invocation of dbs_update() compute the load.
    		 */
    		j_cdbs->prev_load = 0;
    
    		if (ignore_nice)
    			j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
    	}
    
    	gov->start(policy);
    
    	gov_set_update_util(policy_dbs, sampling_rate);
    	return 0;
    }
    EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_start);
    
    void cpufreq_dbs_governor_stop(struct cpufreq_policy *policy)
    {
    	struct policy_dbs_info *policy_dbs = policy->governor_data;
    
    	gov_clear_update_util(policy_dbs->policy);
    	irq_work_sync(&policy_dbs->irq_work);
    	cancel_work_sync(&policy_dbs->work);
    	atomic_set(&policy_dbs->work_count, 0);
    	policy_dbs->work_in_progress = false;
    }
    EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_stop);
    
    void cpufreq_dbs_governor_limits(struct cpufreq_policy *policy)
    {
    	struct policy_dbs_info *policy_dbs = policy->governor_data;
    
    	mutex_lock(&policy_dbs->update_mutex);
    	cpufreq_policy_apply_limits(policy);
    	gov_update_sample_delay(policy_dbs, 0);
    
    	mutex_unlock(&policy_dbs->update_mutex);
    }
    EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_limits);