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Date: Thu, 5 Oct 2023 16:32:55 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Liao Chang <liaochang1@...wei.com>
Cc: rafael@...nel.org, 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 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>
--
viresh
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