diff options
Diffstat (limited to 'drivers/cpufreq/cpufreq_governor.c')
-rw-r--r-- | drivers/cpufreq/cpufreq_governor.c | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index a34de9d10cbc..d41db19a9bb7 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -25,6 +25,69 @@ DEFINE_MUTEX(dbs_data_mutex); EXPORT_SYMBOL_GPL(dbs_data_mutex); +/* Common sysfs tunables */ +/** + * store_sampling_rate - update sampling rate effective immediately if needed. + * + * If new rate is smaller than the old, simply updating + * dbs.sampling_rate might not be appropriate. For example, if the + * original sampling_rate was 1 second and the requested new sampling rate is 10 + * ms because the user needs immediate reaction from ondemand governor, but not + * sure if higher frequency will be required or not, then, the governor may + * change the sampling rate too late; up to 1 second later. Thus, if we are + * reducing the sampling rate, we need to make the new value effective + * immediately. + * + * On the other hand, if new rate is larger than the old, then we may evaluate + * the load too soon, and it might we worth updating sample_delay_ns then as + * well. + * + * This must be called with dbs_data->mutex held, otherwise traversing + * policy_dbs_list isn't safe. + */ +ssize_t store_sampling_rate(struct dbs_data *dbs_data, const char *buf, + size_t count) +{ + struct policy_dbs_info *policy_dbs; + unsigned int rate; + int ret; + ret = sscanf(buf, "%u", &rate); + if (ret != 1) + return -EINVAL; + + dbs_data->sampling_rate = max(rate, dbs_data->min_sampling_rate); + + /* + * We are operating under dbs_data->mutex and so the list and its + * entries can't be freed concurrently. + */ + list_for_each_entry(policy_dbs, &dbs_data->policy_dbs_list, list) { + mutex_lock(&policy_dbs->timer_mutex); + /* + * On 32-bit architectures this may race with the + * sample_delay_ns read in dbs_update_util_handler(), but that + * really doesn't matter. If the read returns a value that's + * too big, the sample will be skipped, but the next invocation + * of dbs_update_util_handler() (when the update has been + * completed) will take a sample. If the returned value is too + * small, the sample will be taken immediately, but that isn't a + * problem, as we want the new rate to take effect immediately + * anyway. + * + * If this runs in parallel with dbs_work_handler(), we may end + * up overwriting the sample_delay_ns value that it has just + * written, but the difference should not be too big and it will + * be corrected next time a sample is taken, so it shouldn't be + * significant. + */ + gov_update_sample_delay(policy_dbs, dbs_data->sampling_rate); + mutex_unlock(&policy_dbs->timer_mutex); + } + + return count; +} +EXPORT_SYMBOL_GPL(store_sampling_rate); + static inline struct dbs_data *to_dbs_data(struct kobject *kobj) { return container_of(kobj, struct dbs_data, kobj); |