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Date: Fri, 6 Oct 2023 22:03:03 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Viresh Kumar <viresh.kumar@...aro.org>,
Liao Chang <liaochang1@...wei.com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] cpufreq: userspace: Use fine-grained mutex in
userspace governor
On Thu, Oct 5, 2023 at 1:05 PM Viresh Kumar <viresh.kumar@...aro.org> 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@...wei.com>
> > ---
> > 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@...aro.org>
Applied as 6.7 material along with the [2/2], thanks!
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