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Message-ID: <20251006105453.648473106@infradead.org>
Date: Mon, 06 Oct 2025 12:46:54 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: tj@...nel.org
Cc: linux-kernel@...r.kernel.org,
peterz@...radead.org,
mingo@...nel.org,
juri.lelli@...hat.com,
vincent.guittot@...aro.org,
dietmar.eggemann@....com,
rostedt@...dmis.org,
bsegall@...gle.com,
mgorman@...e.de,
vschneid@...hat.com,
longman@...hat.com,
hannes@...xchg.org,
mkoutny@...e.com,
void@...ifault.com,
arighi@...dia.com,
changwoo@...lia.com,
cgroups@...r.kernel.org,
sched-ext@...ts.linux.dev,
liuwenfang@...or.com,
tglx@...utronix.de,
Joel Fernandes <joelagnelf@...dia.com>
Subject: [RFC][PATCH 2/3] sched: Add support to pick functions to take rf
From: Joel Fernandes <joelagnelf@...dia.com>
Some pick functions like the internal pick_next_task_fair() already take
rf but some others dont. We need this for scx's server pick function.
Prepare for this by having pick functions accept it.
[peterz: - added RETRY_TASK handling
- removed pick_next_task_fair indirection]
Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
SubmissionLink: https://lkml.kernel.org/r/20250809184800.129831-6-joelagnelf@nvidia.com
---
include/linux/sched.h | 7 ++-----
kernel/sched/core.c | 35 ++++++++++++++++++++++++++---------
kernel/sched/deadline.c | 8 ++++----
kernel/sched/ext.c | 2 +-
kernel/sched/fair.c | 16 ++++++----------
kernel/sched/idle.c | 2 +-
kernel/sched/rt.c | 2 +-
kernel/sched/sched.h | 10 ++++++----
kernel/sched/stop_task.c | 2 +-
9 files changed, 48 insertions(+), 36 deletions(-)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -637,8 +637,8 @@ struct sched_rt_entity {
#endif
} __randomize_layout;
-typedef bool (*dl_server_has_tasks_f)(struct sched_dl_entity *);
-typedef struct task_struct *(*dl_server_pick_f)(struct sched_dl_entity *);
+struct rq_flags;
+typedef struct task_struct *(*dl_server_pick_f)(struct sched_dl_entity *, struct rq_flags *rf);
struct sched_dl_entity {
struct rb_node rb_node;
@@ -730,9 +730,6 @@ struct sched_dl_entity {
* dl_server_update().
*
* @rq the runqueue this server is for
- *
- * @server_has_tasks() returns true if @server_pick return a
- * runnable task.
*/
struct rq *rq;
dl_server_pick_f server_pick_task;
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5901,7 +5901,7 @@ __pick_next_task(struct rq *rq, struct t
/* Assume the next prioritized class is idle_sched_class */
if (!p) {
- p = pick_task_idle(rq);
+ p = pick_task_idle(rq, rf);
put_prev_set_next_task(rq, prev, p);
}
@@ -5913,11 +5913,15 @@ __pick_next_task(struct rq *rq, struct t
for_each_active_class(class) {
if (class->pick_next_task) {
- p = class->pick_next_task(rq, prev);
+ p = class->pick_next_task(rq, prev, rf);
+ if (unlikely(p == RETRY_TASK))
+ goto restart;
if (p)
return p;
} else {
- p = class->pick_task(rq);
+ p = class->pick_task(rq, rf);
+ if (unlikely(p == RETRY_TASK))
+ goto restart;
if (p) {
put_prev_set_next_task(rq, prev, p);
return p;
@@ -5947,7 +5951,11 @@ static inline bool cookie_match(struct t
return a->core_cookie == b->core_cookie;
}
-static inline struct task_struct *pick_task(struct rq *rq)
+/*
+ * Careful; this can return RETRY_TASK, it does not include the retry-loop
+ * itself due to the whole SMT pick retry thing below.
+ */
+static inline struct task_struct *pick_task(struct rq *rq, struct rq_flags *rf)
{
const struct sched_class *class;
struct task_struct *p;
@@ -5955,7 +5963,7 @@ static inline struct task_struct *pick_t
rq->dl_server = NULL;
for_each_active_class(class) {
- p = class->pick_task(rq);
+ p = class->pick_task(rq, rf);
if (p)
return p;
}
@@ -5970,7 +5978,7 @@ static void queue_core_balance(struct rq
static struct task_struct *
pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
{
- struct task_struct *next, *p, *max = NULL;
+ struct task_struct *next, *p, *max;
const struct cpumask *smt_mask;
bool fi_before = false;
bool core_clock_updated = (rq == rq->core);
@@ -6055,7 +6063,10 @@ pick_next_task(struct rq *rq, struct tas
* and there are no cookied tasks running on siblings.
*/
if (!need_sync) {
- next = pick_task(rq);
+restart_single:
+ next = pick_task(rq, rf);
+ if (unlikely(next == RETRY_TASK))
+ goto restart_single;
if (!next->core_cookie) {
rq->core_pick = NULL;
rq->core_dl_server = NULL;
@@ -6075,6 +6086,8 @@ pick_next_task(struct rq *rq, struct tas
*
* Tie-break prio towards the current CPU
*/
+restart_multi:
+ max = NULL;
for_each_cpu_wrap(i, smt_mask, cpu) {
rq_i = cpu_rq(i);
@@ -6086,7 +6099,11 @@ pick_next_task(struct rq *rq, struct tas
if (i != cpu && (rq_i != rq->core || !core_clock_updated))
update_rq_clock(rq_i);
- rq_i->core_pick = p = pick_task(rq_i);
+ p = pick_task(rq_i, rf);
+ if (unlikely(p == RETRY_TASK))
+ goto restart_multi;
+
+ rq_i->core_pick = p;
rq_i->core_dl_server = rq_i->dl_server;
if (!max || prio_less(max, p, fi_before))
@@ -6108,7 +6125,7 @@ pick_next_task(struct rq *rq, struct tas
if (cookie)
p = sched_core_find(rq_i, cookie);
if (!p)
- p = idle_sched_class.pick_task(rq_i);
+ p = idle_sched_class.pick_task(rq_i, rf);
}
rq_i->core_pick = p;
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -2352,7 +2352,7 @@ static struct sched_dl_entity *pick_next
* __pick_next_task_dl - Helper to pick the next -deadline task to run.
* @rq: The runqueue to pick the next task from.
*/
-static struct task_struct *__pick_task_dl(struct rq *rq)
+static struct task_struct *__pick_task_dl(struct rq *rq, struct rq_flags *rf)
{
struct sched_dl_entity *dl_se;
struct dl_rq *dl_rq = &rq->dl;
@@ -2366,7 +2366,7 @@ static struct task_struct *__pick_task_d
WARN_ON_ONCE(!dl_se);
if (dl_server(dl_se)) {
- p = dl_se->server_pick_task(dl_se);
+ p = dl_se->server_pick_task(dl_se, rf);
if (!p) {
dl_server_stop(dl_se);
goto again;
@@ -2379,9 +2379,9 @@ static struct task_struct *__pick_task_d
return p;
}
-static struct task_struct *pick_task_dl(struct rq *rq)
+static struct task_struct *pick_task_dl(struct rq *rq, struct rq_flags *rf)
{
- return __pick_task_dl(rq);
+ return __pick_task_dl(rq, rf);
}
static void put_prev_task_dl(struct rq *rq, struct task_struct *p, struct task_struct *next)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -2332,7 +2332,7 @@ static struct task_struct *first_local_t
struct task_struct, scx.dsq_list.node);
}
-static struct task_struct *pick_task_scx(struct rq *rq)
+static struct task_struct *pick_task_scx(struct rq *rq, struct rq_flags *rf)
{
struct task_struct *prev = rq->curr;
struct task_struct *p;
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8822,7 +8822,7 @@ static void check_preempt_wakeup_fair(st
resched_curr_lazy(rq);
}
-static struct task_struct *pick_task_fair(struct rq *rq)
+static struct task_struct *pick_task_fair(struct rq *rq, struct rq_flags *rf)
{
struct sched_entity *se;
struct cfs_rq *cfs_rq;
@@ -8866,7 +8866,7 @@ pick_next_task_fair(struct rq *rq, struc
int new_tasks;
again:
- p = pick_task_fair(rq);
+ p = pick_task_fair(rq, rf);
if (!p)
goto idle;
se = &p->se;
@@ -8945,14 +8945,10 @@ pick_next_task_fair(struct rq *rq, struc
return NULL;
}
-static struct task_struct *__pick_next_task_fair(struct rq *rq, struct task_struct *prev)
+static struct task_struct *
+fair_server_pick_task(struct sched_dl_entity *dl_se, struct rq_flags *rf)
{
- return pick_next_task_fair(rq, prev, NULL);
-}
-
-static struct task_struct *fair_server_pick_task(struct sched_dl_entity *dl_se)
-{
- return pick_task_fair(dl_se->rq);
+ return pick_task_fair(dl_se->rq, rf);
}
void fair_server_init(struct rq *rq)
@@ -13632,7 +13628,7 @@ DEFINE_SCHED_CLASS(fair) = {
.wakeup_preempt = check_preempt_wakeup_fair,
.pick_task = pick_task_fair,
- .pick_next_task = __pick_next_task_fair,
+ .pick_next_task = pick_next_task_fair,
.put_prev_task = put_prev_task_fair,
.set_next_task = set_next_task_fair,
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -466,7 +466,7 @@ static void set_next_task_idle(struct rq
next->se.exec_start = rq_clock_task(rq);
}
-struct task_struct *pick_task_idle(struct rq *rq)
+struct task_struct *pick_task_idle(struct rq *rq, struct rq_flags *rf)
{
scx_update_idle(rq, true, false);
return rq->idle;
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1695,7 +1695,7 @@ static struct task_struct *_pick_next_ta
return rt_task_of(rt_se);
}
-static struct task_struct *pick_task_rt(struct rq *rq)
+static struct task_struct *pick_task_rt(struct rq *rq, struct rq_flags *rf)
{
struct task_struct *p;
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -2467,7 +2467,7 @@ struct sched_class {
/*
* schedule/pick_next_task: rq->lock
*/
- struct task_struct *(*pick_task)(struct rq *rq);
+ struct task_struct *(*pick_task)(struct rq *rq, struct rq_flags *rf);
/*
* Optional! When implemented pick_next_task() should be equivalent to:
*
@@ -2477,7 +2477,8 @@ struct sched_class {
* set_next_task_first(next);
* }
*/
- struct task_struct *(*pick_next_task)(struct rq *rq, struct task_struct *prev);
+ struct task_struct *(*pick_next_task)(struct rq *rq, struct task_struct *prev,
+ struct rq_flags *rf);
/*
* sched_change:
@@ -2690,8 +2691,9 @@ static inline bool sched_fair_runnable(s
return rq->cfs.nr_queued > 0;
}
-extern struct task_struct *pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf);
-extern struct task_struct *pick_task_idle(struct rq *rq);
+extern struct task_struct *pick_next_task_fair(struct rq *rq, struct task_struct *prev,
+ struct rq_flags *rf);
+extern struct task_struct *pick_task_idle(struct rq *rq, struct rq_flags *rf);
#define SCA_CHECK 0x01
#define SCA_MIGRATE_DISABLE 0x02
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -32,7 +32,7 @@ static void set_next_task_stop(struct rq
stop->se.exec_start = rq_clock_task(rq);
}
-static struct task_struct *pick_task_stop(struct rq *rq)
+static struct task_struct *pick_task_stop(struct rq *rq, struct rq_flags *rf)
{
if (!sched_stop_runnable(rq))
return NULL;
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