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-rw-r--r--kernel/sched/cpufreq_schedutil.c152
1 files changed, 107 insertions, 45 deletions
diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 6192e0ed7a7c..416b7d7853d4 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -51,7 +51,7 @@ struct sugov_cpu {
bool iowait_boost_pending;
unsigned int iowait_boost;
unsigned int iowait_boost_max;
- u64 last_update;
+ u64 last_update;
/* The fields below are only needed when sharing a policy: */
unsigned long util_cfs;
@@ -196,45 +196,120 @@ static unsigned long sugov_aggregate_util(struct sugov_cpu *sg_cpu)
return min(util, sg_cpu->max);
}
-static void sugov_set_iowait_boost(struct sugov_cpu *sg_cpu, u64 time, unsigned int flags)
+/**
+ * sugov_iowait_reset() - Reset the IO boost status of a CPU.
+ * @sg_cpu: the sugov data for the CPU to boost
+ * @time: the update time from the caller
+ * @set_iowait_boost: true if an IO boost has been requested
+ *
+ * The IO wait boost of a task is disabled after a tick since the last update
+ * of a CPU. If a new IO wait boost is requested after more then a tick, then
+ * we enable the boost starting from the minimum frequency, which improves
+ * energy efficiency by ignoring sporadic wakeups from IO.
+ */
+static bool sugov_iowait_reset(struct sugov_cpu *sg_cpu, u64 time,
+ bool set_iowait_boost)
{
- /* Clear iowait_boost if the CPU apprears to have been idle. */
- if (sg_cpu->iowait_boost) {
- s64 delta_ns = time - sg_cpu->last_update;
+ s64 delta_ns = time - sg_cpu->last_update;
- if (delta_ns > TICK_NSEC) {
- sg_cpu->iowait_boost = 0;
- sg_cpu->iowait_boost_pending = false;
- }
- }
+ /* Reset boost only if a tick has elapsed since last request */
+ if (delta_ns <= TICK_NSEC)
+ return false;
- if (flags & SCHED_CPUFREQ_IOWAIT) {
- if (sg_cpu->iowait_boost_pending)
- return;
+ sg_cpu->iowait_boost = set_iowait_boost
+ ? sg_cpu->sg_policy->policy->min : 0;
+ sg_cpu->iowait_boost_pending = set_iowait_boost;
- sg_cpu->iowait_boost_pending = true;
+ return true;
+}
- if (sg_cpu->iowait_boost) {
- sg_cpu->iowait_boost <<= 1;
- if (sg_cpu->iowait_boost > sg_cpu->iowait_boost_max)
- sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
- } else {
- sg_cpu->iowait_boost = sg_cpu->sg_policy->policy->min;
- }
+/**
+ * sugov_iowait_boost() - Updates the IO boost status of a CPU.
+ * @sg_cpu: the sugov data for the CPU to boost
+ * @time: the update time from the caller
+ * @flags: SCHED_CPUFREQ_IOWAIT if the task is waking up after an IO wait
+ *
+ * Each time a task wakes up after an IO operation, the CPU utilization can be
+ * boosted to a certain utilization which doubles at each "frequent and
+ * successive" wakeup from IO, ranging from the utilization of the minimum
+ * OPP to the utilization of the maximum OPP.
+ * To keep doubling, an IO boost has to be requested at least once per tick,
+ * otherwise we restart from the utilization of the minimum OPP.
+ */
+static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, u64 time,
+ unsigned int flags)
+{
+ bool set_iowait_boost = flags & SCHED_CPUFREQ_IOWAIT;
+
+ /* Reset boost if the CPU appears to have been idle enough */
+ if (sg_cpu->iowait_boost &&
+ sugov_iowait_reset(sg_cpu, time, set_iowait_boost))
+ return;
+
+ /* Boost only tasks waking up after IO */
+ if (!set_iowait_boost)
+ return;
+
+ /* Ensure boost doubles only one time at each request */
+ if (sg_cpu->iowait_boost_pending)
+ return;
+ sg_cpu->iowait_boost_pending = true;
+
+ /* Double the boost at each request */
+ if (sg_cpu->iowait_boost) {
+ sg_cpu->iowait_boost <<= 1;
+ if (sg_cpu->iowait_boost > sg_cpu->iowait_boost_max)
+ sg_cpu->iowait_boost = sg_cpu->iowait_boost_max;
+ return;
}
+
+ /* First wakeup after IO: start with minimum boost */
+ sg_cpu->iowait_boost = sg_cpu->sg_policy->policy->min;
}
-static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, unsigned long *util,
- unsigned long *max)
+/**
+ * sugov_iowait_apply() - Apply the IO boost to a CPU.
+ * @sg_cpu: the sugov data for the cpu to boost
+ * @time: the update time from the caller
+ * @util: the utilization to (eventually) boost
+ * @max: the maximum value the utilization can be boosted to
+ *
+ * A CPU running a task which woken up after an IO operation can have its
+ * utilization boosted to speed up the completion of those IO operations.
+ * The IO boost value is increased each time a task wakes up from IO, in
+ * sugov_iowait_apply(), and it's instead decreased by this function,
+ * each time an increase has not been requested (!iowait_boost_pending).
+ *
+ * A CPU which also appears to have been idle for at least one tick has also
+ * its IO boost utilization reset.
+ *
+ * This mechanism is designed to boost high frequently IO waiting tasks, while
+ * being more conservative on tasks which does sporadic IO operations.
+ */
+static void sugov_iowait_apply(struct sugov_cpu *sg_cpu, u64 time,
+ unsigned long *util, unsigned long *max)
{
unsigned int boost_util, boost_max;
+ /* No boost currently required */
if (!sg_cpu->iowait_boost)
return;
+ /* Reset boost if the CPU appears to have been idle enough */
+ if (sugov_iowait_reset(sg_cpu, time, false))
+ return;
+
+ /*
+ * An IO waiting task has just woken up:
+ * allow to further double the boost value
+ */
if (sg_cpu->iowait_boost_pending) {
sg_cpu->iowait_boost_pending = false;
} else {
+ /*
+ * Otherwise: reduce the boost value and disable it when we
+ * reach the minimum.
+ */
sg_cpu->iowait_boost >>= 1;
if (sg_cpu->iowait_boost < sg_cpu->sg_policy->policy->min) {
sg_cpu->iowait_boost = 0;
@@ -242,9 +317,12 @@ static void sugov_iowait_boost(struct sugov_cpu *sg_cpu, unsigned long *util,
}
}
+ /*
+ * Apply the current boost value: a CPU is boosted only if its current
+ * utilization is smaller then the current IO boost level.
+ */
boost_util = sg_cpu->iowait_boost;
boost_max = sg_cpu->iowait_boost_max;
-
if (*util * boost_max < *max * boost_util) {
*util = boost_util;
*max = boost_max;
@@ -283,7 +361,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
unsigned int next_f;
bool busy;
- sugov_set_iowait_boost(sg_cpu, time, flags);
+ sugov_iowait_boost(sg_cpu, time, flags);
sg_cpu->last_update = time;
ignore_dl_rate_limit(sg_cpu, sg_policy);
@@ -296,7 +374,7 @@ static void sugov_update_single(struct update_util_data *hook, u64 time,
sugov_get_util(sg_cpu);
max = sg_cpu->max;
util = sugov_aggregate_util(sg_cpu);
- sugov_iowait_boost(sg_cpu, &util, &max);
+ sugov_iowait_apply(sg_cpu, time, &util, &max);
next_f = get_next_freq(sg_policy, util, max);
/*
* Do not reduce the frequency if the CPU has not been idle
@@ -322,28 +400,12 @@ static unsigned int sugov_next_freq_shared(struct sugov_cpu *sg_cpu, u64 time)
for_each_cpu(j, policy->cpus) {
struct sugov_cpu *j_sg_cpu = &per_cpu(sugov_cpu, j);
unsigned long j_util, j_max;
- s64 delta_ns;
sugov_get_util(j_sg_cpu);
-
- /*
- * If the CFS CPU utilization was last updated before the
- * previous frequency update and the time elapsed between the
- * last update of the CPU utilization and the last frequency
- * update is long enough, reset iowait_boost and util_cfs, as
- * they are now probably stale. However, still consider the
- * CPU contribution if it has some DEADLINE utilization
- * (util_dl).
- */
- delta_ns = time - j_sg_cpu->last_update;
- if (delta_ns > TICK_NSEC) {
- j_sg_cpu->iowait_boost = 0;
- j_sg_cpu->iowait_boost_pending = false;
- }
-
j_max = j_sg_cpu->max;
j_util = sugov_aggregate_util(j_sg_cpu);
- sugov_iowait_boost(j_sg_cpu, &j_util, &j_max);
+ sugov_iowait_apply(j_sg_cpu, time, &j_util, &j_max);
+
if (j_util * max > j_max * util) {
util = j_util;
max = j_max;
@@ -362,7 +424,7 @@ sugov_update_shared(struct update_util_data *hook, u64 time, unsigned int flags)
raw_spin_lock(&sg_policy->update_lock);
- sugov_set_iowait_boost(sg_cpu, time, flags);
+ sugov_iowait_boost(sg_cpu, time, flags);
sg_cpu->last_update = time;
ignore_dl_rate_limit(sg_cpu, sg_policy);