Re: [PATCH 1/2] cpufreq: userspace: Use fine-grained mutex in userspace governor

[Rafael J. Wysocki]

On Thu, Oct 5, 2023 at 1:05 PM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>
> On 12-09-23, 06:10, Liao Chang wrote:
> > The userspace governor currently uses a big global mutex to avoid the
> > race condition on the governor_data field of cpufreq_policy structure.
> > This leads to a low concurrency if multiple userspace applications are
> > trying to set the speed of different policies at the same time. This
> > patch introduces a per-policy mutex to allow the updating of different
> > policies to be performed concurrently, improving overall concurrency.
> >
> > Signed-off-by: Liao Chang <liaochang1@xxxxxxxxxx>
> > ---
> >  drivers/cpufreq/cpufreq_userspace.c | 69 +++++++++++++++++------------
> >  1 file changed, 40 insertions(+), 29 deletions(-)
> >
> > diff --git a/drivers/cpufreq/cpufreq_userspace.c b/drivers/cpufreq/cpufreq_userspace.c
> > index 50a4d7846580..442e31060d62 100644
> > --- a/drivers/cpufreq/cpufreq_userspace.c
> > +++ b/drivers/cpufreq/cpufreq_userspace.c
> > @@ -16,7 +16,11 @@
> >  #include <linux/slab.h>
> >
> >  static DEFINE_PER_CPU(unsigned int, cpu_is_managed);
> > -static DEFINE_MUTEX(userspace_mutex);
> > +
> > +struct userspace_policy {
> > +     unsigned int setspeed;
> > +     struct mutex mutex;
> > +};
> >
> >  /**
> >   * cpufreq_set - set the CPU frequency
> > @@ -28,19 +32,19 @@ static DEFINE_MUTEX(userspace_mutex);
> >  static int cpufreq_set(struct cpufreq_policy *policy, unsigned int freq)
> >  {
> >       int ret = -EINVAL;
> > -     unsigned int *setspeed = policy->governor_data;
> > +     struct userspace_policy *userspace = policy->governor_data;
> >
> >       pr_debug("cpufreq_set for cpu %u, freq %u kHz\n", policy->cpu, freq);
> >
> > -     mutex_lock(&userspace_mutex);
> > +     mutex_lock(&userspace->mutex);
> >       if (!per_cpu(cpu_is_managed, policy->cpu))
> >               goto err;
> >
> > -     *setspeed = freq;
> > +     userspace->setspeed = freq;
> >
> >       ret = __cpufreq_driver_target(policy, freq, CPUFREQ_RELATION_L);
> >   err:
> > -     mutex_unlock(&userspace_mutex);
> > +     mutex_unlock(&userspace->mutex);
> >       return ret;
> >  }
> >
> > @@ -51,67 +55,74 @@ static ssize_t show_speed(struct cpufreq_policy *policy, char *buf)
> >
> >  static int cpufreq_userspace_policy_init(struct cpufreq_policy *policy)
> >  {
> > -     unsigned int *setspeed;
> > +     struct userspace_policy *userspace;
> >
> > -     setspeed = kzalloc(sizeof(*setspeed), GFP_KERNEL);
> > -     if (!setspeed)
> > +     userspace = kzalloc(sizeof(*userspace), GFP_KERNEL);
> > +     if (!userspace)
> >               return -ENOMEM;
> >
> > -     policy->governor_data = setspeed;
> > +     mutex_init(&userspace->mutex);
> > +
> > +     policy->governor_data = userspace;
> >       return 0;
> >  }
> >
> > +/*
> > + * Any routine that writes to the policy struct will hold the "rwsem" of
> > + * policy struct that means it is free to free "governor_data" here.
> > + */
> >  static void cpufreq_userspace_policy_exit(struct cpufreq_policy *policy)
> >  {
> > -     mutex_lock(&userspace_mutex);
> >       kfree(policy->governor_data);
> >       policy->governor_data = NULL;
> > -     mutex_unlock(&userspace_mutex);
> >  }
> >
> >  static int cpufreq_userspace_policy_start(struct cpufreq_policy *policy)
> >  {
> > -     unsigned int *setspeed = policy->governor_data;
> > +     struct userspace_policy *userspace = policy->governor_data;
> >
> >       BUG_ON(!policy->cur);
> >       pr_debug("started managing cpu %u\n", policy->cpu);
> >
> > -     mutex_lock(&userspace_mutex);
> > +     mutex_lock(&userspace->mutex);
> >       per_cpu(cpu_is_managed, policy->cpu) = 1;
> > -     *setspeed = policy->cur;
> > -     mutex_unlock(&userspace_mutex);
> > +     userspace->setspeed = policy->cur;
> > +     mutex_unlock(&userspace->mutex);
> >       return 0;
> >  }
> >
> >  static void cpufreq_userspace_policy_stop(struct cpufreq_policy *policy)
> >  {
> > -     unsigned int *setspeed = policy->governor_data;
> > +     struct userspace_policy *userspace = policy->governor_data;
> >
> >       pr_debug("managing cpu %u stopped\n", policy->cpu);
> >
> > -     mutex_lock(&userspace_mutex);
> > +     mutex_lock(&userspace->mutex);
> >       per_cpu(cpu_is_managed, policy->cpu) = 0;
> > -     *setspeed = 0;
> > -     mutex_unlock(&userspace_mutex);
> > +     userspace->setspeed = 0;
> > +     mutex_unlock(&userspace->mutex);
> >  }
> >
> >  static void cpufreq_userspace_policy_limits(struct cpufreq_policy *policy)
> >  {
> > -     unsigned int *setspeed = policy->governor_data;
> > +     struct userspace_policy *userspace = policy->governor_data;
> >
> > -     mutex_lock(&userspace_mutex);
> > +     mutex_lock(&userspace->mutex);
> >
> >       pr_debug("limit event for cpu %u: %u - %u kHz, currently %u kHz, last set to %u kHz\n",
> > -              policy->cpu, policy->min, policy->max, policy->cur, *setspeed);
> > -
> > -     if (policy->max < *setspeed)
> > -             __cpufreq_driver_target(policy, policy->max, CPUFREQ_RELATION_H);
> > -     else if (policy->min > *setspeed)
> > -             __cpufreq_driver_target(policy, policy->min, CPUFREQ_RELATION_L);
> > +              policy->cpu, policy->min, policy->max, policy->cur, userspace->setspeed);
> > +
> > +     if (policy->max < userspace->setspeed)
> > +             __cpufreq_driver_target(policy, policy->max,
> > +                                     CPUFREQ_RELATION_H);
> > +     else if (policy->min > userspace->setspeed)
> > +             __cpufreq_driver_target(policy, policy->min,
> > +                                     CPUFREQ_RELATION_L);
> >       else
> > -             __cpufreq_driver_target(policy, *setspeed, CPUFREQ_RELATION_L);
> > +             __cpufreq_driver_target(policy, userspace->setspeed,
> > +                                     CPUFREQ_RELATION_L);
> >
> > -     mutex_unlock(&userspace_mutex);
> > +     mutex_unlock(&userspace->mutex);
> >  }
> >
> >  static struct cpufreq_governor cpufreq_gov_userspace = {
>
> Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>

Applied as 6.7 material along with the [2/2], thanks!