Am Donnerstag, den 29.10.2015, 17:57 +0530 schrieb Viresh Kumar: > cpufreq governors evaluate load at sampling rate and based on that they > update frequency for a group of CPUs belonging to the same cpufreq > policy. > > This is required to be done in a single thread for all policy->cpus, but > because we don't want to wakeup idle CPUs to do just that, we use > deferrable work for this. If we would have used a single delayed > deferrable work for the entire policy, there were chances that the CPU > required to run the handler can be in idle and we might end up not > changing the frequency for the entire group with load variations. > > And so we were forced to keep per-cpu works, and only the one that > expires first need to do the real work and others are rescheduled for > next sampling time. > > We have been using the more complex solution until now, where we used a > delayed deferrable work for this, which is a combination of a timer and > a work. > > This could be made lightweight by keeping per-cpu deferred timers with a > single work item, which is scheduled by the first timer that expires. > > This patch does just that and here are important changes: > - The timer handler will run in irq context and so we need to use a > spin_lock instead of the timer_mutex. And so a separate timer_lock is > created. This also makes the use of the mutex and lock quite clear, as > we know what exactly they are protecting. > - A new field 'skip_work' is added to track when the timer handlers can > queue a work. More comments present in code. >
I don't want to block this patch on that, but maybe as a thought for further consideration: Wouldn't it make sense to use a single unbound deferrable work item for this? There was some work to make this possible already: "timer: make deferrable cpu unbound timers really not bound to a cpu" Regards, Lucas > Suggested-by: Rafael J. Wysocki <[email protected]> > Signed-off-by: Viresh Kumar <[email protected]> > --- > drivers/cpufreq/cpufreq_governor.c | 139 > +++++++++++++++++++++---------------- > drivers/cpufreq/cpufreq_governor.h | 20 ++++-- > drivers/cpufreq/cpufreq_ondemand.c | 8 +-- > 3 files changed, 98 insertions(+), 69 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq_governor.c > b/drivers/cpufreq/cpufreq_governor.c > index 999e1f6addf9..a3f9bc9b98e9 100644 > --- a/drivers/cpufreq/cpufreq_governor.c > +++ b/drivers/cpufreq/cpufreq_governor.c > @@ -158,47 +158,52 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu) > } > EXPORT_SYMBOL_GPL(dbs_check_cpu); > > -static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data, > - unsigned int delay) > +void gov_add_timers(struct cpufreq_policy *policy, unsigned int delay) > { > - struct cpu_dbs_info *cdbs = dbs_data->cdata->get_cpu_cdbs(cpu); > - > - mod_delayed_work_on(cpu, system_wq, &cdbs->dwork, delay); > -} > - > -void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy, > - unsigned int delay, bool all_cpus) > -{ > - int i; > + struct dbs_data *dbs_data = policy->governor_data; > + struct cpu_dbs_info *cdbs; > + int cpu; > > - if (!all_cpus) { > - /* > - * Use raw_smp_processor_id() to avoid preemptible warnings. > - * We know that this is only called with all_cpus == false from > - * works that have been queued with *_work_on() functions and > - * those works are canceled during CPU_DOWN_PREPARE so they > - * can't possibly run on any other CPU. > - */ > - __gov_queue_work(raw_smp_processor_id(), dbs_data, delay); > - } else { > - for_each_cpu(i, policy->cpus) > - __gov_queue_work(i, dbs_data, delay); > + 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); > } > } > -EXPORT_SYMBOL_GPL(gov_queue_work); > +EXPORT_SYMBOL_GPL(gov_add_timers); > > -static inline void gov_cancel_work(struct dbs_data *dbs_data, > - struct cpufreq_policy *policy) > +static inline void gov_cancel_timers(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); > - cancel_delayed_work_sync(&cdbs->dwork); > + del_timer_sync(&cdbs->timer); > } > } > > +void gov_cancel_work(struct cpu_common_dbs_info *shared) > +{ > + unsigned long flags; > + > + /* > + * No work will be queued from timer handlers after skip_work is > + * updated. And so we can safely cancel the work first and then the > + * timers. > + */ > + spin_lock_irqsave(&shared->timer_lock, flags); > + shared->skip_work++; > + spin_unlock_irqrestore(&shared->timer_lock, flags); > + > + cancel_work_sync(&shared->work); > + > + gov_cancel_timers(shared->policy); > + > + shared->skip_work = 0; > +} > + > /* 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) > @@ -217,29 +222,21 @@ static bool need_load_eval(struct cpu_common_dbs_info > *shared, > return true; > } > > -static void dbs_timer(struct work_struct *work) > +static void dbs_work_handler(struct work_struct *work) > { > - struct cpu_dbs_info *cdbs = container_of(work, struct cpu_dbs_info, > - dwork.work); > - struct cpu_common_dbs_info *shared = cdbs->shared; > + struct cpu_common_dbs_info *shared = container_of(work, struct > + cpu_common_dbs_info, work); > struct cpufreq_policy *policy; > struct dbs_data *dbs_data; > unsigned int sampling_rate, delay; > - bool modify_all = true; > - > - mutex_lock(&shared->timer_mutex); > + bool eval_load; > > policy = shared->policy; > - > - /* > - * Governor might already be disabled and there is no point continuing > - * with the work-handler. > - */ > - if (!policy) > - goto unlock; > - > 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; > > @@ -250,14 +247,44 @@ static void dbs_timer(struct work_struct *work) > sampling_rate = od_tuners->sampling_rate; > } > > - if (!need_load_eval(cdbs->shared, sampling_rate)) > - modify_all = false; > + eval_load = need_load_eval(shared, sampling_rate); > > - delay = dbs_data->cdata->gov_dbs_timer(policy, modify_all); > - gov_queue_work(dbs_data, policy, delay, modify_all); > + /* > + * Make sure cpufreq_governor_limits() isn't evaluating load in > + * parallel. > + */ > + mutex_lock(&shared->timer_mutex); > + delay = dbs_data->cdata->gov_dbs_timer(policy, eval_load); > + mutex_unlock(&shared->timer_mutex); > + > + shared->skip_work--; > + gov_add_timers(policy, delay); > +} > + > +static void dbs_timer_handler(unsigned long data) > +{ > + struct cpu_dbs_info *cdbs = (struct cpu_dbs_info *)data; > + struct cpu_common_dbs_info *shared = cdbs->shared; > + struct cpufreq_policy *policy; > + unsigned long flags; > + > + spin_lock_irqsave(&shared->timer_lock, flags); > + policy = shared->policy; > + > + /* > + * Timer handler isn't allowed to queue work at the moment, because: > + * - Another timer handler has done that > + * - We are stopping the governor > + * - Or we are updating the sampling rate of ondemand governor > + */ > + if (shared->skip_work) > + goto unlock; > + > + shared->skip_work++; > + queue_work(system_wq, &shared->work); > > unlock: > - mutex_unlock(&shared->timer_mutex); > + spin_unlock_irqrestore(&shared->timer_lock, flags); > } > > static void set_sampling_rate(struct dbs_data *dbs_data, > @@ -288,6 +315,8 @@ static int alloc_common_dbs_info(struct cpufreq_policy > *policy, > cdata->get_cpu_cdbs(j)->shared = shared; > > mutex_init(&shared->timer_mutex); > + spin_lock_init(&shared->timer_lock); > + INIT_WORK(&shared->work, dbs_work_handler); > return 0; > } > > @@ -452,7 +481,9 @@ static int cpufreq_governor_start(struct cpufreq_policy > *policy, > if (ignore_nice) > j_cdbs->prev_cpu_nice = > kcpustat_cpu(j).cpustat[CPUTIME_NICE]; > > - INIT_DEFERRABLE_WORK(&j_cdbs->dwork, dbs_timer); > + __setup_timer(&j_cdbs->timer, dbs_timer_handler, > + (unsigned long)j_cdbs, > + TIMER_DEFERRABLE | TIMER_IRQSAFE); > } > > if (cdata->governor == GOV_CONSERVATIVE) { > @@ -470,8 +501,7 @@ static int cpufreq_governor_start(struct cpufreq_policy > *policy, > od_ops->powersave_bias_init_cpu(cpu); > } > > - gov_queue_work(dbs_data, policy, delay_for_sampling_rate(sampling_rate), > - true); > + gov_add_timers(policy, delay_for_sampling_rate(sampling_rate)); > return 0; > } > > @@ -485,16 +515,9 @@ static int cpufreq_governor_stop(struct cpufreq_policy > *policy, > if (!shared || !shared->policy) > return -EBUSY; > > - /* > - * Work-handler must see this updated, as it should not proceed any > - * further after governor is disabled. And so timer_mutex is taken while > - * updating this value. > - */ > - mutex_lock(&shared->timer_mutex); > + gov_cancel_work(shared); > shared->policy = NULL; > - mutex_unlock(&shared->timer_mutex); > > - gov_cancel_work(dbs_data, policy); > return 0; > } > > diff --git a/drivers/cpufreq/cpufreq_governor.h > b/drivers/cpufreq/cpufreq_governor.h > index 0c7589016b6c..76742902491e 100644 > --- a/drivers/cpufreq/cpufreq_governor.h > +++ b/drivers/cpufreq/cpufreq_governor.h > @@ -132,12 +132,20 @@ static void *get_cpu_dbs_info_s(int cpu) > \ > struct cpu_common_dbs_info { > struct cpufreq_policy *policy; > /* > - * percpu mutex that serializes governor limit change with dbs_timer > - * invocation. We do not want dbs_timer to run when user is changing > - * the governor or limits. > + * Per policy mutex that serializes load evaluation from limit-change > + * and work-handler. > */ > struct mutex timer_mutex; > + > + /* > + * Per policy lock that serializes access to queuing work from timer > + * handlers. > + */ > + spinlock_t timer_lock; > + > ktime_t time_stamp; > + unsigned int skip_work; > + struct work_struct work; > }; > > /* Per cpu structures */ > @@ -152,7 +160,7 @@ struct cpu_dbs_info { > * wake-up from idle. > */ > unsigned int prev_load; > - struct delayed_work dwork; > + struct timer_list timer; > struct cpu_common_dbs_info *shared; > }; > > @@ -268,11 +276,11 @@ static ssize_t show_sampling_rate_min_gov_pol > \ > > extern struct mutex cpufreq_governor_lock; > > +void gov_add_timers(struct cpufreq_policy *policy, unsigned int delay); > +void gov_cancel_work(struct cpu_common_dbs_info *shared); > void dbs_check_cpu(struct dbs_data *dbs_data, int cpu); > int cpufreq_governor_dbs(struct cpufreq_policy *policy, > struct common_dbs_data *cdata, unsigned int event); > -void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy, > - unsigned int delay, bool all_cpus); > void od_register_powersave_bias_handler(unsigned int (*f) > (struct cpufreq_policy *, unsigned int, unsigned int), > unsigned int powersave_bias); > diff --git a/drivers/cpufreq/cpufreq_ondemand.c > b/drivers/cpufreq/cpufreq_ondemand.c > index 0848c8ac6847..9e0293c23285 100644 > --- a/drivers/cpufreq/cpufreq_ondemand.c > +++ b/drivers/cpufreq/cpufreq_ondemand.c > @@ -285,13 +285,11 @@ static void update_sampling_rate(struct dbs_data > *dbs_data, > continue; > > next_sampling = jiffies + usecs_to_jiffies(new_rate); > - appointed_at = dbs_info->cdbs.dwork.timer.expires; > + appointed_at = dbs_info->cdbs.timer.expires; > > if (time_before(next_sampling, appointed_at)) { > - cancel_delayed_work_sync(&dbs_info->cdbs.dwork); > - > - gov_queue_work(dbs_data, policy, > - usecs_to_jiffies(new_rate), true); > + gov_cancel_work(shared); > + gov_add_timers(policy, usecs_to_jiffies(new_rate)); > > } > } -- Pengutronix e.K. | Lucas Stach | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
