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path: root/drivers/cpufreq/cpufreq_governor.c
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Diffstat (limited to 'drivers/cpufreq/cpufreq_governor.c')
-rw-r--r--drivers/cpufreq/cpufreq_governor.c117
1 files changed, 64 insertions, 53 deletions
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 20f0a4e114d1..be498d56dd69 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -103,7 +103,7 @@ void gov_update_cpu_data(struct dbs_data *dbs_data)
for_each_cpu(j, policy_dbs->policy->cpus) {
struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
- j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_cpu_wall,
+ j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_update_time,
dbs_data->io_is_busy);
if (dbs_data->ignore_nice_load)
j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
@@ -137,21 +137,17 @@ unsigned int dbs_update(struct cpufreq_policy *policy)
/* Get Absolute Load */
for_each_cpu(j, policy->cpus) {
struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
- u64 cur_wall_time, cur_idle_time;
- unsigned int idle_time, wall_time;
+ u64 update_time, cur_idle_time;
+ unsigned int idle_time, time_elapsed;
unsigned int load;
- cur_idle_time = get_cpu_idle_time(j, &cur_wall_time, io_busy);
+ cur_idle_time = get_cpu_idle_time(j, &update_time, io_busy);
- wall_time = cur_wall_time - j_cdbs->prev_cpu_wall;
- j_cdbs->prev_cpu_wall = cur_wall_time;
+ time_elapsed = update_time - j_cdbs->prev_update_time;
+ j_cdbs->prev_update_time = update_time;
- if (cur_idle_time <= j_cdbs->prev_cpu_idle) {
- idle_time = 0;
- } else {
- idle_time = cur_idle_time - j_cdbs->prev_cpu_idle;
- j_cdbs->prev_cpu_idle = cur_idle_time;
- }
+ idle_time = cur_idle_time - j_cdbs->prev_cpu_idle;
+ j_cdbs->prev_cpu_idle = cur_idle_time;
if (ignore_nice) {
u64 cur_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
@@ -160,47 +156,62 @@ unsigned int dbs_update(struct cpufreq_policy *policy)
j_cdbs->prev_cpu_nice = cur_nice;
}
- if (unlikely(!wall_time || wall_time < idle_time))
- continue;
-
- /*
- * If the CPU had gone completely idle, and a task just woke up
- * on this CPU now, it would be unfair to calculate 'load' the
- * usual way for this elapsed time-window, because it will show
- * near-zero load, irrespective of how CPU intensive that task
- * actually is. This is undesirable for latency-sensitive bursty
- * workloads.
- *
- * To avoid this, we reuse the 'load' from the previous
- * time-window and give this task a chance to start with a
- * reasonably high CPU frequency. (However, we shouldn't over-do
- * this copy, lest we get stuck at a high load (high frequency)
- * for too long, even when the current system load has actually
- * dropped down. So we perform the copy only once, upon the
- * first wake-up from idle.)
- *
- * Detecting this situation is easy: the governor's utilization
- * update handler would not have run during CPU-idle periods.
- * Hence, an unusually large 'wall_time' (as compared to the
- * sampling rate) indicates this scenario.
- *
- * prev_load can be zero in two cases and we must recalculate it
- * for both cases:
- * - during long idle intervals
- * - explicitly set to zero
- */
- if (unlikely(wall_time > (2 * sampling_rate) &&
- j_cdbs->prev_load)) {
+ if (unlikely(!time_elapsed)) {
+ /*
+ * That can only happen when this function is called
+ * twice in a row with a very short interval between the
+ * calls, so the previous load value can be used then.
+ */
load = j_cdbs->prev_load;
-
+ } else if (unlikely(time_elapsed > 2 * sampling_rate &&
+ j_cdbs->prev_load)) {
/*
- * Perform a destructive copy, to ensure that we copy
- * the previous load only once, upon the first wake-up
- * from idle.
+ * If the CPU had gone completely idle and a task has
+ * just woken up on this CPU now, it would be unfair to
+ * calculate 'load' the usual way for this elapsed
+ * time-window, because it would show near-zero load,
+ * irrespective of how CPU intensive that task actually
+ * was. This is undesirable for latency-sensitive bursty
+ * workloads.
+ *
+ * To avoid this, reuse the 'load' from the previous
+ * time-window and give this task a chance to start with
+ * a reasonably high CPU frequency. However, that
+ * shouldn't be over-done, lest we get stuck at a high
+ * load (high frequency) for too long, even when the
+ * current system load has actually dropped down, so
+ * clear prev_load to guarantee that the load will be
+ * computed again next time.
+ *
+ * Detecting this situation is easy: the governor's
+ * utilization update handler would not have run during
+ * CPU-idle periods. Hence, an unusually large
+ * 'time_elapsed' (as compared to the sampling rate)
+ * indicates this scenario.
*/
+ load = j_cdbs->prev_load;
j_cdbs->prev_load = 0;
} else {
- load = 100 * (wall_time - idle_time) / wall_time;
+ if (time_elapsed >= idle_time) {
+ load = 100 * (time_elapsed - idle_time) / time_elapsed;
+ } else {
+ /*
+ * That can happen if idle_time is returned by
+ * get_cpu_idle_time_jiffy(). In that case
+ * idle_time is roughly equal to the difference
+ * between time_elapsed and "busy time" obtained
+ * from CPU statistics. Then, the "busy time"
+ * can end up being greater than time_elapsed
+ * (for example, if jiffies_64 and the CPU
+ * statistics are updated by different CPUs),
+ * so idle_time may in fact be negative. That
+ * means, though, that the CPU was busy all
+ * the time (on the rough average) during the
+ * last sampling interval and 100 can be
+ * returned as the load.
+ */
+ load = (int)idle_time < 0 ? 100 : 0;
+ }
j_cdbs->prev_load = load;
}
@@ -512,12 +523,12 @@ static int cpufreq_governor_start(struct cpufreq_policy *policy)
for_each_cpu(j, policy->cpus) {
struct cpu_dbs_info *j_cdbs = &per_cpu(cpu_dbs, j);
- unsigned int prev_load;
- j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_cpu_wall, io_busy);
-
- prev_load = j_cdbs->prev_cpu_wall - j_cdbs->prev_cpu_idle;
- j_cdbs->prev_load = 100 * prev_load / (unsigned int)j_cdbs->prev_cpu_wall;
+ j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_update_time, io_busy);
+ /*
+ * Make the first invocation of dbs_update() compute the load.
+ */
+ j_cdbs->prev_load = 0;
if (ignore_nice)
j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE];
generated by cgit v1.2.3 (git 2.51.0) at 2025-09-20 04:55:05 +0000