Re: [PATCH 03/10] cpufreq: conservative: remove 'enable' field
From: Preeti U Murthy <hidden>
Date: 2015-06-26 05:57:55
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
quoted hunk ↗ jump to hunk
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 */