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Date: Tue, 08 Sep 2015 03:11:49 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Viresh Kumar <viresh.kumar@...aro.org>
Cc: linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
preeti.lkml@...il.com, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 3/9] cpufreq: ondemand: only queue canceled works from update_sampling_rate()
On Monday, July 27, 2015 05:58:08 PM Viresh Kumar wrote:
> The sampling rate is updated with a call to update_sampling_rate(), and
> we process CPUs one by one here. While the work is canceled on per-cpu
> basis, it is getting queued (by mistake) for all policy->cpus.
>
> This would result in wasting cpu cycles for queuing works which are
> already queued and never canceled.
>
> This patch changes this behavior to queue work only on the cpu, for
> which it was canceled earlier.
>
> To do that, replace 'modify_all' parameter to gov_queue_work() with a
> mask of CPUs.
There really are two cases, either you pass a CPU or gov_queue_work() has to
walk policy->cpus. Doing it the way you did hides that IMO.
I'd simply pass an int and use a special value to indicate that policy->cpus
is to be walked.
> Also the last parameter to ->gov_dbs_timer() was named
> 'modify_all' earlier, but its purpose was to decide if load has to be
> evaluated again or not. Lets rename that to load_eval.
>
> Fixes: 031299b3be30 ("cpufreq: governors: Avoid unnecessary per cpu timer interrupts")
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> drivers/cpufreq/cpufreq_conservative.c | 4 ++--
> drivers/cpufreq/cpufreq_governor.c | 30 ++++++++++--------------------
> drivers/cpufreq/cpufreq_governor.h | 4 ++--
> drivers/cpufreq/cpufreq_ondemand.c | 7 ++++---
> 4 files changed, 18 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
> index 18bfbc313e48..1aa3bd46cea3 100644
> --- a/drivers/cpufreq/cpufreq_conservative.c
> +++ b/drivers/cpufreq/cpufreq_conservative.c
> @@ -116,11 +116,11 @@ static void cs_check_cpu(int cpu, unsigned int load)
> }
>
> static unsigned int cs_dbs_timer(struct cpu_dbs_info *cdbs,
> - struct dbs_data *dbs_data, bool modify_all)
> + struct dbs_data *dbs_data, bool load_eval)
> {
> struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
>
> - if (modify_all)
> + if (load_eval)
> dbs_check_cpu(dbs_data, cdbs->shared->policy->cpu);
>
> return delay_for_sampling_rate(cs_tuners->sampling_rate);
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index 750626d8fb03..a890450711bb 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -167,7 +167,7 @@ static inline void __gov_queue_work(int cpu, struct dbs_data *dbs_data,
> }
>
> void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
> - unsigned int delay, bool all_cpus)
> + unsigned int delay, const struct cpumask *cpus)
> {
> int i;
>
> @@ -175,19 +175,8 @@ void gov_queue_work(struct dbs_data *dbs_data, struct cpufreq_policy *policy,
> if (!policy->governor_enabled)
> goto out_unlock;
>
> - 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.
> - */
This was a useful comment and it should be moved along the logic it was supposed
to explain and not just dropped.
> - __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(i, cpus)
> + __gov_queue_work(i, dbs_data, delay);
>
> out_unlock:
> mutex_unlock(&cpufreq_governor_lock);
> @@ -232,7 +221,8 @@ static void dbs_timer(struct work_struct *work)
> struct cpufreq_policy *policy = shared->policy;
> struct dbs_data *dbs_data = policy->governor_data;
> unsigned int sampling_rate, delay;
> - bool modify_all = true;
> + const struct cpumask *cpus;
I don't think this local variable is necessary.
> + bool load_eval;
>
> mutex_lock(&shared->timer_mutex);
>
> @@ -246,11 +236,11 @@ 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;
> + load_eval = need_load_eval(cdbs->shared, sampling_rate);
> + cpus = load_eval ? policy->cpus : cpumask_of(raw_smp_processor_id());
>
> - delay = dbs_data->cdata->gov_dbs_timer(cdbs, dbs_data, modify_all);
> - gov_queue_work(dbs_data, policy, delay, modify_all);
> + delay = dbs_data->cdata->gov_dbs_timer(cdbs, dbs_data, load_eval);
> + gov_queue_work(dbs_data, policy, delay, cpus);
>
> mutex_unlock(&shared->timer_mutex);
> }
> @@ -474,7 +464,7 @@ static int cpufreq_governor_start(struct cpufreq_policy *policy,
> }
>
> gov_queue_work(dbs_data, policy, delay_for_sampling_rate(sampling_rate),
> - true);
> + policy->cpus);
> return 0;
> }
>
> diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
> index 5621bb03e874..52665a0624b2 100644
> --- a/drivers/cpufreq/cpufreq_governor.h
> +++ b/drivers/cpufreq/cpufreq_governor.h
> @@ -211,7 +211,7 @@ struct common_dbs_data {
> void *(*get_cpu_dbs_info_s)(int cpu);
> unsigned int (*gov_dbs_timer)(struct cpu_dbs_info *cdbs,
> struct dbs_data *dbs_data,
> - bool modify_all);
> + bool load_eval);
> void (*gov_check_cpu)(int cpu, unsigned int load);
> int (*init)(struct dbs_data *dbs_data, bool notify);
> void (*exit)(struct dbs_data *dbs_data, bool notify);
> @@ -273,7 +273,7 @@ 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);
> + unsigned int delay, const struct cpumask *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 1fa9088c84a8..2474c9c34022 100644
> --- a/drivers/cpufreq/cpufreq_ondemand.c
> +++ b/drivers/cpufreq/cpufreq_ondemand.c
> @@ -192,7 +192,7 @@ static void od_check_cpu(int cpu, unsigned int load)
> }
>
> static unsigned int od_dbs_timer(struct cpu_dbs_info *cdbs,
> - struct dbs_data *dbs_data, bool modify_all)
> + struct dbs_data *dbs_data, bool load_eval)
> {
> struct cpufreq_policy *policy = cdbs->shared->policy;
> unsigned int cpu = policy->cpu;
> @@ -201,7 +201,7 @@ static unsigned int od_dbs_timer(struct cpu_dbs_info *cdbs,
> struct od_dbs_tuners *od_tuners = dbs_data->tuners;
> int delay = 0, sample_type = dbs_info->sample_type;
>
> - if (!modify_all)
> + if (!load_eval)
> goto max_delay;
>
> /* Common NORMAL_SAMPLE setup */
> @@ -284,7 +284,8 @@ static void update_sampling_rate(struct dbs_data *dbs_data,
> mutex_lock(&dbs_info->cdbs.shared->timer_mutex);
>
> gov_queue_work(dbs_data, policy,
> - usecs_to_jiffies(new_rate), true);
> + usecs_to_jiffies(new_rate),
> + cpumask_of(cpu));
>
> }
> mutex_unlock(&dbs_info->cdbs.shared->timer_mutex);
>
Thanks,
Rafael
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