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Message-Id: <20241011061145.998428-1-xavier_qy@163.com>
Date: Fri, 11 Oct 2024 14:11:45 +0800
From: Xavier <xavier_qy@....com>
To: peterz@...radead.org,
mingo@...hat.com,
juri.lelli@...hat.com,
vincent.guittot@...aro.org,
dietmar.eggemann@....com,
rostedt@...dmis.org,
bsegall@...gle.com,
mgorman@...e.de,
vschneid@...hat.com,
yu.c.chen@...el.com
Cc: linux-kernel@...r.kernel.org,
xw357835 <xw357835@...baba-inc.com>
Subject: [PATCH v2] sched/eevdf: Reduce the computation frequency of avg_vruntime
From: xw357835 <xw357835@...baba-inc.com>
The current code subtracts the value of curr from avg_vruntime and avg_load
during runtime. Then, every time avg_vruntime() is called, it adds the
value of curr to the avg_vruntime and avg_load. Afterward, it divides these
and adds min_vruntime to obtain the actual avg_vruntime.
Analysis of the code indicates that avg_vruntime only changes significantly
during update_curr(), update_min_vruntime(), and when tasks are enqueued or
dequeued. Therefore, it is sufficient to recalculate and store avg_vruntime
only in these specific scenarios. This optimization ensures that accessing
avg_vruntime() does not necessitate a recalculation each time, thereby
enhancing the efficiency of the code.
There is no need to subtract curr’s load from avg_load during runtime.
Instead, we only need to calculate the incremental change and update
avg_vruntime whenever curr’s time is updated.
To better represent their functions, rename the original avg_vruntime and
avg_load to tot_vruntime and tot_load, respectively, which more accurately
describes their roles in the computation.
Signed-off-by: xw357835 <xw357835@...baba-inc.com>
---
Note:
The patch V2 has been updated based on the latest sched/core branch.
kernel/sched/fair.c | 107 ++++++++++++++++++++++++-------------------
kernel/sched/sched.h | 3 +-
2 files changed, 61 insertions(+), 49 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5a621210c9c..fb0434dd0a8 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -606,8 +606,8 @@ static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
* Which we track using:
*
* v0 := cfs_rq->min_vruntime
- * \Sum (v_i - v0) * w_i := cfs_rq->avg_vruntime
- * \Sum w_i := cfs_rq->avg_load
+ * \Sum (v_i - v0) * w_i := cfs_rq->tot_vruntime
+ * \Sum w_i := cfs_rq->tot_load
*
* Since min_vruntime is a monotonic increasing variable that closely tracks
* the per-task service, these deltas: (v_i - v), will be in the order of the
@@ -617,14 +617,29 @@ static inline s64 entity_key(struct cfs_rq *cfs_rq, struct sched_entity *se)
*
* As measured, the max (key * weight) value was ~44 bits for a kernel build.
*/
+static inline void avg_vruntime_update(struct cfs_rq *cfs_rq)
+{
+ s64 tot_vruntime = cfs_rq->tot_vruntime;
+
+ /* sign flips effective floor / ceiling */
+ if (cfs_rq->tot_load) {
+ if (tot_vruntime < 0)
+ tot_vruntime -= (cfs_rq->tot_load - 1);
+ cfs_rq->avg_vruntime = div_s64(tot_vruntime, cfs_rq->tot_load);
+ } else {
+ cfs_rq->avg_vruntime = cfs_rq->tot_vruntime;
+ }
+}
+
static void
avg_vruntime_add(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
unsigned long weight = scale_load_down(se->load.weight);
s64 key = entity_key(cfs_rq, se);
- cfs_rq->avg_vruntime += key * weight;
- cfs_rq->avg_load += weight;
+ cfs_rq->tot_vruntime += key * weight;
+ cfs_rq->tot_load += weight;
+ avg_vruntime_update(cfs_rq);
}
static void
@@ -633,17 +648,29 @@ avg_vruntime_sub(struct cfs_rq *cfs_rq, struct sched_entity *se)
unsigned long weight = scale_load_down(se->load.weight);
s64 key = entity_key(cfs_rq, se);
- cfs_rq->avg_vruntime -= key * weight;
- cfs_rq->avg_load -= weight;
+ cfs_rq->tot_vruntime -= key * weight;
+ cfs_rq->tot_load -= weight;
+ avg_vruntime_update(cfs_rq);
+}
+
+static inline
+void avg_vruntime_update_for_curr(struct cfs_rq *cfs_rq, s64 delta)
+{
+ struct sched_entity *curr = cfs_rq->curr;
+ unsigned long weight = scale_load_down(curr->load.weight);
+
+ cfs_rq->tot_vruntime += delta * weight;
+ avg_vruntime_update(cfs_rq);
}
static inline
-void avg_vruntime_update(struct cfs_rq *cfs_rq, s64 delta)
+void avg_vruntime_update_for_minv(struct cfs_rq *cfs_rq, s64 delta)
{
/*
- * v' = v + d ==> avg_vruntime' = avg_runtime - d*avg_load
+ * v' = v + d ==> avg_runtime' = tot_runtime - d*tot_load
*/
- cfs_rq->avg_vruntime -= cfs_rq->avg_load * delta;
+ cfs_rq->tot_vruntime -= cfs_rq->tot_load * delta;
+ avg_vruntime_update(cfs_rq);
}
/*
@@ -652,25 +679,7 @@ void avg_vruntime_update(struct cfs_rq *cfs_rq, s64 delta)
*/
u64 avg_vruntime(struct cfs_rq *cfs_rq)
{
- struct sched_entity *curr = cfs_rq->curr;
- s64 avg = cfs_rq->avg_vruntime;
- long load = cfs_rq->avg_load;
-
- if (curr && curr->on_rq) {
- unsigned long weight = scale_load_down(curr->load.weight);
-
- avg += entity_key(cfs_rq, curr) * weight;
- load += weight;
- }
-
- if (load) {
- /* sign flips effective floor / ceiling */
- if (avg < 0)
- avg -= (load - 1);
- avg = div_s64(avg, load);
- }
-
- return cfs_rq->min_vruntime + avg;
+ return cfs_rq->min_vruntime + cfs_rq->avg_vruntime;
}
/*
@@ -725,18 +734,8 @@ static void update_entity_lag(struct cfs_rq *cfs_rq, struct sched_entity *se)
*/
static int vruntime_eligible(struct cfs_rq *cfs_rq, u64 vruntime)
{
- struct sched_entity *curr = cfs_rq->curr;
- s64 avg = cfs_rq->avg_vruntime;
- long load = cfs_rq->avg_load;
-
- if (curr && curr->on_rq) {
- unsigned long weight = scale_load_down(curr->load.weight);
-
- avg += entity_key(cfs_rq, curr) * weight;
- load += weight;
- }
-
- return avg >= (s64)(vruntime - cfs_rq->min_vruntime) * load;
+ return cfs_rq->tot_vruntime >=
+ (s64)(vruntime - cfs_rq->min_vruntime) * (s64)cfs_rq->tot_load;
}
int entity_eligible(struct cfs_rq *cfs_rq, struct sched_entity *se)
@@ -752,7 +751,7 @@ static u64 __update_min_vruntime(struct cfs_rq *cfs_rq, u64 vruntime)
*/
s64 delta = (s64)(vruntime - min_vruntime);
if (delta > 0) {
- avg_vruntime_update(cfs_rq, delta);
+ avg_vruntime_update_for_minv(cfs_rq, delta);
min_vruntime = vruntime;
}
return min_vruntime;
@@ -851,7 +850,6 @@ RB_DECLARE_CALLBACKS(static, min_vruntime_cb, struct sched_entity,
*/
static void __enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
- avg_vruntime_add(cfs_rq, se);
se->min_vruntime = se->vruntime;
se->min_slice = se->slice;
rb_add_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
@@ -862,7 +860,6 @@ static void __dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
rb_erase_augmented_cached(&se->run_node, &cfs_rq->tasks_timeline,
&min_vruntime_cb);
- avg_vruntime_sub(cfs_rq, se);
}
struct sched_entity *__pick_root_entity(struct cfs_rq *cfs_rq)
@@ -1219,6 +1216,7 @@ static void update_curr(struct cfs_rq *cfs_rq)
struct rq *rq = rq_of(cfs_rq);
s64 delta_exec;
bool resched;
+ s64 vdelta_exec;
if (unlikely(!curr))
return;
@@ -1227,8 +1225,10 @@ static void update_curr(struct cfs_rq *cfs_rq)
if (unlikely(delta_exec <= 0))
return;
- curr->vruntime += calc_delta_fair(delta_exec, curr);
+ vdelta_exec = calc_delta_fair(delta_exec, curr);
+ curr->vruntime += vdelta_exec;
resched = update_deadline(cfs_rq, curr);
+ avg_vruntime_update_for_curr(cfs_rq, vdelta_exec);
update_min_vruntime(cfs_rq);
if (entity_is_task(curr)) {
@@ -3883,6 +3883,8 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
avruntime = avg_vruntime(cfs_rq);
if (!curr)
__dequeue_entity(cfs_rq, se);
+
+ avg_vruntime_sub(cfs_rq, se);
update_load_sub(&cfs_rq->load, se->load.weight);
}
dequeue_load_avg(cfs_rq, se);
@@ -3913,6 +3915,8 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
if (!curr)
__enqueue_entity(cfs_rq, se);
+ avg_vruntime_add(cfs_rq, se);
+
/*
* The entity's vruntime has been adjusted, so let's check
* whether the rq-wide min_vruntime needs updated too. Since
@@ -5281,7 +5285,6 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
* EEVDF: placement strategy #1 / #2
*/
if (sched_feat(PLACE_LAG) && cfs_rq->nr_running && se->vlag) {
- struct sched_entity *curr = cfs_rq->curr;
unsigned long load;
lag = se->vlag;
@@ -5338,9 +5341,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
*
* vl_i = (W + w_i)*vl'_i / W
*/
- load = cfs_rq->avg_load;
- if (curr && curr->on_rq)
- load += scale_load_down(curr->load.weight);
+ load = cfs_rq->tot_load;
lag *= load + scale_load_down(se->load.weight);
if (WARN_ON_ONCE(!load))
@@ -5427,6 +5428,8 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
update_stats_enqueue_fair(cfs_rq, se, flags);
if (!curr)
__enqueue_entity(cfs_rq, se);
+
+ avg_vruntime_add(cfs_rq, se);
se->on_rq = 1;
if (cfs_rq->nr_running == 1) {
@@ -5530,6 +5533,8 @@ dequeue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
if (se != cfs_rq->curr)
__dequeue_entity(cfs_rq, se);
+
+ avg_vruntime_sub(cfs_rq, se);
se->on_rq = 0;
account_entity_dequeue(cfs_rq, se);
@@ -6924,11 +6929,17 @@ requeue_delayed_entity(struct sched_entity *se)
cfs_rq->nr_running--;
if (se != cfs_rq->curr)
__dequeue_entity(cfs_rq, se);
+ avg_vruntime_sub(cfs_rq, se);
+
se->vlag = 0;
place_entity(cfs_rq, se, 0);
+
if (se != cfs_rq->curr)
__enqueue_entity(cfs_rq, se);
+ avg_vruntime_add(cfs_rq, se);
cfs_rq->nr_running++;
+
+ update_min_vruntime(cfs_rq);
}
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index b1c3588a8f0..7f7c93518c7 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -650,8 +650,9 @@ struct cfs_rq {
unsigned int idle_nr_running; /* SCHED_IDLE */
unsigned int idle_h_nr_running; /* SCHED_IDLE */
+ s64 tot_vruntime;
s64 avg_vruntime;
- u64 avg_load;
+ u64 tot_load;
u64 min_vruntime;
#ifdef CONFIG_SCHED_CORE
--
2.45.2
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