Re: [PATCH 03/10] cpufreq: conservative: remove 'enable' field

On 06/22/2015 01:32 PM, Viresh Kumar wrote:

Conservative governor has its own 'enable' field to check two things:

• If conservative governor is used for a CPU or not
• If governor is currently enabled or not, as there can be a race around the notifier being called while it was getting unregistered from cpufreq_governor_dbs().

The race is between changing governors in cpufreq_set_policy() and the notifier being called, isn't it ? The governor will get unregistered when we remove the cpufreq module and here too we do not set policy->governor to NULL nor set the enable bit to 0. So it does not look like we were protecting these checks against un-registering the governor.

The first one can be checked by comparing policy->governor with 'cpufreq_gov_conservative' and the second one isn't that important. In the worst case, we will end up updating dbs_info->requested_freq. And that wouldn't do any harm.

Assuming the race that exists is indeed the one that I mentioned above, it does not look like we will hit this case where we end up updating the requested_freq unnecessarily.

stop conservative governor :

policy->governor is conservative. STOP gov_cancel_work() ----> The notifiers will not run after this point. enable = 0

So while the notifiers are running, they will see that the policy->governor is conservative and that enable = 1.

start conservative governor :

START enable = 1 gov_start_work() ----> The notifiers will run after this point only.

So when they run, they will see that policy->governor = conservative and enable = 1.

Both the fields are consistent with each other when notifiers run. It thus looks like this patch will not bring about a difference in the functionality, hence harmless.

Regards Preeti U Murthy

Lets get rid of this field.

Signed-off-by: Viresh Kumar viresh.kumar@linaro.org

drivers/cpufreq/cpufreq_conservative.c | 26 +++++++++++++++----------- drivers/cpufreq/cpufreq_governor.c | 12 +----------- drivers/cpufreq/cpufreq_governor.h | 1 - 3 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c index 1e3cabfb2b57..f53719e5bed9 100644 --- a/drivers/cpufreq/cpufreq_conservative.c +++ b/drivers/cpufreq/cpufreq_conservative.c @@ -23,6 +23,19 @@

static DEFINE_PER_CPU(struct cs_cpu_dbs_info_s, cs_cpu_dbs_info);

+static int cs_cpufreq_governor_dbs(struct cpufreq_policy *policy,

• 		   unsigned int event);
  

+#ifndef CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE +static +#endif +struct cpufreq_governor cpufreq_gov_conservative = {

• .name = "conservative",
• .governor = cs_cpufreq_governor_dbs,
• .max_transition_latency = TRANSITION_LATENCY_LIMIT,
• .owner = THIS_MODULE,

+};

static inline unsigned int get_freq_target(struct cs_dbs_tuners *cs_tuners, struct cpufreq_policy *policy) { @@ -124,7 +137,8 @@ static int dbs_cpufreq_notifier(struct notifier_block *nb, unsigned long val, if (!policy) return 0;

• if (!dbs_info->enable)

• /* policy isn't governed by conservative governor */

• if (policy->governor != &cpufreq_gov_conservative) goto policy_put;

  /*

@@ -371,16 +385,6 @@ static int cs_cpufreq_governor_dbs(struct cpufreq_policy *policy, return cpufreq_governor_dbs(policy, &cs_dbs_cdata, event); }

-#ifndef CONFIG_CPU_FREQ_DEFAULT_GOV_CONSERVATIVE -static -#endif -struct cpufreq_governor cpufreq_gov_conservative = {

• .name = "conservative",
• .governor = cs_cpufreq_governor_dbs,
• .max_transition_latency = TRANSITION_LATENCY_LIMIT,
• .owner = THIS_MODULE,

-};

static int __init cpufreq_gov_dbs_init(void) { return cpufreq_register_governor(&cpufreq_gov_conservative); diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index af63402a94a9..836aefd03c1b 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -463,7 +463,6 @@ static int cpufreq_governor_start(struct cpufreq_policy *policy, cdata->get_cpu_dbs_info_s(cpu);

cs_dbs_info->down_skip = 0;

• cs_dbs_info->enable = 1;
  

  cs_dbs_info->requested_freq = policy->cur; } else { struct od_ops *od_ops = cdata->gov_ops;

@@ -482,9 +481,7 @@ static int cpufreq_governor_start(struct cpufreq_policy *policy, static int cpufreq_governor_stop(struct cpufreq_policy *policy, struct dbs_data *dbs_data) {

• struct common_dbs_data *cdata = dbs_data->cdata;
• unsigned int cpu = policy->cpu;
• struct cpu_dbs_info *cdbs = cdata->get_cpu_cdbs(cpu);

• struct cpu_dbs_info *cdbs = dbs_data->cdata->get_cpu_cdbs(policy->cpu); struct cpu_common_dbs_info *ccdbs = cdbs->ccdbs;

  /* State should be equivalent to START */

@@ -493,13 +490,6 @@ static int cpufreq_governor_stop(struct cpufreq_policy *policy,

gov_cancel_work(dbs_data, policy);

• if (cdata->governor == GOV_CONSERVATIVE) {

• struct cs_cpu_dbs_info_s *cs_dbs_info =
  

• 	cdata->get_cpu_dbs_info_s(cpu);
  

• cs_dbs_info->enable = 0;
  

• }
• ccdbs->policy = NULL; mutex_destroy(&ccdbs->timer_mutex); return 0;

diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h index 2125c299c602..a0d24149f18c 100644 --- a/drivers/cpufreq/cpufreq_governor.h +++ b/drivers/cpufreq/cpufreq_governor.h @@ -170,7 +170,6 @@ struct cs_cpu_dbs_info_s { struct cpu_dbs_info cdbs; unsigned int down_skip; unsigned int requested_freq;

• unsigned int enable:1;

};

/* Per policy Governors sysfs tunables */