On 03-02-16, 02:16, Rafael J. Wysocki wrote:
> Index: linux-pm/drivers/cpufreq/cpufreq_governor.c
> -void gov_add_timers(struct cpufreq_policy *policy, unsigned int delay)
> +void gov_set_update_util(struct cpu_common_dbs_info *shared,
> + unsigned int delay_us)
> {
> + struct cpufreq_policy *policy = shared->policy;
> struct dbs_data *dbs_data = policy->governor_data;
> - struct cpu_dbs_info *cdbs;
> int cpu;
>
> + shared->sample_delay_ns = delay_us * NSEC_PER_USEC;
> + shared->time_stamp = ktime_get();
> +
> for_each_cpu(cpu, policy->cpus) {
> - cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
> - cdbs->timer.expires = jiffies + delay;
> - add_timer_on(&cdbs->timer, cpu);
> + struct cpu_dbs_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu);
> +
> + cdbs->last_sample_time = 0;
> + cpufreq_set_update_util_data(cpu, &cdbs->update_util);
Why no synchronize_rcu() here? This can be called from ondemand
governor on sampling-rate updates ..
> }
> }
> -EXPORT_SYMBOL_GPL(gov_add_timers);
> +EXPORT_SYMBOL_GPL(gov_set_update_util);
>
> -static inline void gov_cancel_timers(struct cpufreq_policy *policy)
> +static inline void gov_clear_update_util(struct cpufreq_policy *policy)
> {
> - struct dbs_data *dbs_data = policy->governor_data;
> - struct cpu_dbs_info *cdbs;
> int i;
>
> - for_each_cpu(i, policy->cpus) {
> - cdbs = dbs_data->cdata->get_cpu_cdbs(i);
> - del_timer_sync(&cdbs->timer);
> - }
> + for_each_cpu(i, policy->cpus)
> + cpufreq_set_update_util_data(i, NULL);
> +
> + synchronize_rcu();
> }
>
> void gov_cancel_work(struct cpu_common_dbs_info *shared)
> {
> - /* Tell dbs_timer_handler() to skip queuing up work items. */
> + /* Tell dbs_update_util_handler() to skip queuing up work items. */
> atomic_inc(&shared->skip_work);
> /*
> - * If dbs_timer_handler() is already running, it may not notice the
> - * incremented skip_work, so wait for it to complete to prevent its work
> - * item from being queued up after the cancel_work_sync() below.
> - */
> - gov_cancel_timers(shared->policy);
> - /*
> - * In case dbs_timer_handler() managed to run and spawn a work item
> - * before the timers have been canceled, wait for that work item to
> - * complete and then cancel all of the timers set up by it. If
> - * dbs_timer_handler() runs again at that point, it will see the
> - * positive value of skip_work and won't spawn any more work items.
> + * If dbs_update_util_handler() is already running, it may not notice
> + * the incremented skip_work, so wait for it to complete to prevent its
> + * work item from being queued up after the cancel_work_sync() below.
> */
> + gov_clear_update_util(shared->policy);
> cancel_work_sync(&shared->work);
How are we sure that the irq-work can't be pending at this point of
time, which will queue the above works again ?
> - gov_cancel_timers(shared->policy);
> atomic_set(&shared->skip_work, 0);
> }
> EXPORT_SYMBOL_GPL(gov_cancel_work);
>
> -/* Will return if we need to evaluate cpu load again or not */
> -static bool need_load_eval(struct cpu_common_dbs_info *shared,
> - unsigned int sampling_rate)
> -{
> - if (policy_is_shared(shared->policy)) {
> - ktime_t time_now = ktime_get();
> - s64 delta_us = ktime_us_delta(time_now, shared->time_stamp);
> -
> - /* Do nothing if we recently have sampled */
> - if (delta_us < (s64)(sampling_rate / 2))
> - return false;
> - else
> - shared->time_stamp = time_now;
> - }
> -
> - return true;
> -}
> -
> static void dbs_work_handler(struct work_struct *work)
> {
> struct cpu_common_dbs_info *shared = container_of(work, struct
> @@ -235,14 +212,10 @@ static void dbs_work_handler(struct work
> struct cpufreq_policy *policy;
> struct dbs_data *dbs_data;
> unsigned int sampling_rate, delay;
> - bool eval_load;
>
> policy = shared->policy;
> dbs_data = policy->governor_data;
>
> - /* Kill all timers */
> - gov_cancel_timers(policy);
> -
> if (dbs_data->cdata->governor == GOV_CONSERVATIVE) {
> struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
>
> @@ -253,37 +226,53 @@ static void dbs_work_handler(struct work
> sampling_rate = od_tuners->sampling_rate;
> }
>
> - eval_load = need_load_eval(shared, sampling_rate);
> -
> /*
> - * Make sure cpufreq_governor_limits() isn't evaluating load in
> + * Make sure cpufreq_governor_limits() isn't evaluating load or the
> + * ondemand governor isn't reading the time stamp and sampling rate in
> * parallel.
> */
> mutex_lock(&shared->timer_mutex);
> - delay = dbs_data->cdata->gov_dbs_timer(policy, eval_load);
> + delay = dbs_data->cdata->gov_dbs_timer(policy);
> + shared->sample_delay_ns = jiffies_to_nsecs(delay);
> + shared->time_stamp = ktime_get();
> mutex_unlock(&shared->timer_mutex);
>
> + smp_mb__before_atomic();
And why is this required exactly ? Maybe a comment as well to clarify
this as this isn't obvious ?
> atomic_dec(&shared->skip_work);
> +}
>
> - gov_add_timers(policy, delay);
> +static void dbs_irq_work(struct irq_work *irq_work)
> +{
> + struct cpu_common_dbs_info *shared;
> +
> + shared = container_of(irq_work, struct cpu_common_dbs_info, irq_work);
> + schedule_work(&shared->work);
> }
>
> -static void dbs_timer_handler(unsigned long data)
> +static void dbs_update_util_handler(struct update_util_data *data, u64 time,
> + unsigned long util, unsigned long max)
> {
> - struct cpu_dbs_info *cdbs = (struct cpu_dbs_info *)data;
> + struct cpu_dbs_info *cdbs = container_of(data, struct cpu_dbs_info,
> update_util);
> struct cpu_common_dbs_info *shared = cdbs->shared;
>
> /*
> - * Timer handler may not be allowed to queue the work at the moment,
> - * because:
> - * - Another timer handler has done that
> - * - We are stopping the governor
> - * - Or we are updating the sampling rate of the ondemand governor
> + * The work may not be allowed to be queued up right now.
> + * Possible reasons:
> + * - Work has already been queued up or is in progress.
> + * - The governor is being stopped.
> + * - It is too early (too little time from the previous sample).
> */
> - if (atomic_inc_return(&shared->skip_work) > 1)
> - atomic_dec(&shared->skip_work);
> - else
> - queue_work(system_wq, &shared->work);
> + if (atomic_inc_return(&shared->skip_work) == 1) {
> + u64 delta_ns;
> +
> + delta_ns = time - cdbs->last_sample_time;
> + if ((s64)delta_ns >= shared->sample_delay_ns) {
> + cdbs->last_sample_time = time;
> + irq_work_queue_on(&shared->irq_work,
> smp_processor_id());
> + return;
> + }
> + }
> + atomic_dec(&shared->skip_work);
> }
>
> static void set_sampling_rate(struct dbs_data *dbs_data,
> @@ -467,9 +456,6 @@ static int cpufreq_governor_start(struct
> io_busy = od_tuners->io_is_busy;
> }
>
> - shared->policy = policy;
> - shared->time_stamp = ktime_get();
> -
> for_each_cpu(j, policy->cpus) {
> struct cpu_dbs_info *j_cdbs = cdata->get_cpu_cdbs(j);
> unsigned int prev_load;
> @@ -485,10 +471,10 @@ static int cpufreq_governor_start(struct
> if (ignore_nice)
> j_cdbs->prev_cpu_nice =
> kcpustat_cpu(j).cpustat[CPUTIME_NICE];
>
> - __setup_timer(&j_cdbs->timer, dbs_timer_handler,
> - (unsigned long)j_cdbs,
> - TIMER_DEFERRABLE | TIMER_IRQSAFE);
> + j_cdbs->update_util.func = dbs_update_util_handler;
> }
> + shared->policy = policy;
> + init_irq_work(&shared->irq_work, dbs_irq_work);
>
> if (cdata->governor == GOV_CONSERVATIVE) {
> struct cs_cpu_dbs_info_s *cs_dbs_info =
> @@ -505,7 +491,7 @@ static int cpufreq_governor_start(struct
> od_ops->powersave_bias_init_cpu(cpu);
> }
>
> - gov_add_timers(policy, delay_for_sampling_rate(sampling_rate));
> + gov_set_update_util(shared, sampling_rate);
> return 0;
> }
>
> Index: linux-pm/drivers/cpufreq/cpufreq_ondemand.c
> ===================================================================
> --- linux-pm.orig/drivers/cpufreq/cpufreq_ondemand.c
> +++ linux-pm/drivers/cpufreq/cpufreq_ondemand.c
> @@ -191,7 +191,7 @@ static void od_check_cpu(int cpu, unsign
> }
> }
>
> -static unsigned int od_dbs_timer(struct cpufreq_policy *policy, bool
> modify_all)
> +static unsigned int od_dbs_timer(struct cpufreq_policy *policy)
> {
> struct dbs_data *dbs_data = policy->governor_data;
> unsigned int cpu = policy->cpu;
> @@ -200,9 +200,6 @@ static unsigned int od_dbs_timer(struct
> struct od_dbs_tuners *od_tuners = dbs_data->tuners;
> int delay = 0, sample_type = dbs_info->sample_type;
Perhaps, the delay = 0 can be dropped now and ...
>
> - if (!modify_all)
> - goto max_delay;
> -
> /* Common NORMAL_SAMPLE setup */
> dbs_info->sample_type = OD_NORMAL_SAMPLE;
> if (sample_type == OD_SUB_SAMPLE) {
> @@ -218,7 +215,6 @@ static unsigned int od_dbs_timer(struct
> }
> }
>
> -max_delay:
> if (!delay)
> delay = delay_for_sampling_rate(od_tuners->sampling_rate
> * dbs_info->rate_mult);
^^ can be moved to the else part of above block ..
> @@ -264,7 +260,7 @@ static void update_sampling_rate(struct
> struct od_cpu_dbs_info_s *dbs_info;
> struct cpu_dbs_info *cdbs;
> struct cpu_common_dbs_info *shared;
> - unsigned long next_sampling, appointed_at;
> + ktime_t next_sampling, appointed_at;
>
> dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
> cdbs = &dbs_info->cdbs;
> @@ -292,16 +288,19 @@ static void update_sampling_rate(struct
> continue;
>
> /*
> - * Checking this for any CPU should be fine, timers for all of
> - * them are scheduled together.
> + * Checking this for any CPU sharing the policy should be fine,
> + * they are all scheduled to sample at the same time.
> */
> - next_sampling = jiffies + usecs_to_jiffies(new_rate);
> - appointed_at = dbs_info->cdbs.timer.expires;
> + next_sampling = ktime_add_us(ktime_get(), new_rate);
>
> - if (time_before(next_sampling, appointed_at)) {
> - gov_cancel_work(shared);
> - gov_add_timers(policy, usecs_to_jiffies(new_rate));
> + mutex_lock(&shared->timer_mutex);
Why is taking this lock important here ?
> + appointed_at = ktime_add_ns(shared->time_stamp,
Also I failed to understand why we need time_stamp variable at all?
Why can't we use last_sample_time ?
> + shared->sample_delay_ns);
> + mutex_unlock(&shared->timer_mutex);
>
> + if (ktime_before(next_sampling, appointed_at)) {
> + gov_cancel_work(shared);
> + gov_set_update_util(shared, new_rate);
You don't need to a complete update here, the pointers are all fine.
> }
> }
--
viresh
