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Message-ID: <20250722070600.3267819-7-jstultz@google.com>
Date: Tue, 22 Jul 2025 07:05:52 +0000
From: John Stultz <jstultz@...gle.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: John Stultz <jstultz@...gle.com>, Joel Fernandes <joelagnelf@...dia.com>,
Qais Yousef <qyousef@...alina.io>, Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
Valentin Schneider <vschneid@...hat.com>, Steven Rostedt <rostedt@...dmis.org>,
Ben Segall <bsegall@...gle.com>, Zimuzo Ezeozue <zezeozue@...gle.com>, Mel Gorman <mgorman@...e.de>,
Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>, Boqun Feng <boqun.feng@...il.com>,
"Paul E. McKenney" <paulmck@...nel.org>, Metin Kaya <Metin.Kaya@....com>,
Xuewen Yan <xuewen.yan94@...il.com>, K Prateek Nayak <kprateek.nayak@....com>,
Thomas Gleixner <tglx@...utronix.de>, Daniel Lezcano <daniel.lezcano@...aro.org>,
Suleiman Souhlal <suleiman@...gle.com>, kuyo chang <kuyo.chang@...iatek.com>, hupu <hupu.gm@...il.com>,
kernel-team@...roid.com
Subject: [RFC][PATCH v20 6/6] sched: Migrate whole chain in proxy_migrate_task()
Instead of migrating one task each time through find_proxy_task(),
we can walk up the blocked_donor ptrs and migrate the entire
current chain in one go.
This was broken out of earlier patches and held back while the
series was being stabilized, but I wanted to re-introduce it.
Signed-off-by: John Stultz <jstultz@...gle.com>
---
v12:
* Earlier this was re-using blocked_node, but I hit
a race with activating blocked entities, and to
avoid it introduced a new migration_node listhead
v18:
* Add init_task initialization of migration_node as suggested
by Suleiman
Cc: Joel Fernandes <joelagnelf@...dia.com>
Cc: Qais Yousef <qyousef@...alina.io>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Valentin Schneider <vschneid@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ben Segall <bsegall@...gle.com>
Cc: Zimuzo Ezeozue <zezeozue@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: "Paul E. McKenney" <paulmck@...nel.org>
Cc: Metin Kaya <Metin.Kaya@....com>
Cc: Xuewen Yan <xuewen.yan94@...il.com>
Cc: K Prateek Nayak <kprateek.nayak@....com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
Cc: Suleiman Souhlal <suleiman@...gle.com>
Cc: kuyo chang <kuyo.chang@...iatek.com>
Cc: hupu <hupu.gm@...il.com>
Cc: kernel-team@...roid.com
---
include/linux/sched.h | 1 +
init/init_task.c | 1 +
kernel/fork.c | 1 +
kernel/sched/core.c | 25 +++++++++++++++++--------
4 files changed, 20 insertions(+), 8 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 675e2f89ec0f8..e9242dfa5f271 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1240,6 +1240,7 @@ struct task_struct {
enum blocked_on_state blocked_on_state;
struct mutex *blocked_on; /* lock we're blocked on */
struct task_struct *blocked_donor; /* task that is boosting this task */
+ struct list_head migration_node;
raw_spinlock_t blocked_lock;
#ifdef CONFIG_DETECT_HUNG_TASK_BLOCKER
diff --git a/init/init_task.c b/init/init_task.c
index 627bbd8953e88..65e0f90285966 100644
--- a/init/init_task.c
+++ b/init/init_task.c
@@ -176,6 +176,7 @@ struct task_struct init_task __aligned(L1_CACHE_BYTES) = {
#endif
.blocked_on_state = BO_RUNNABLE,
.blocked_donor = NULL,
+ .migration_node = LIST_HEAD_INIT(init_task.migration_node),
#ifdef CONFIG_RT_MUTEXES
.pi_waiters = RB_ROOT_CACHED,
.pi_top_task = NULL,
diff --git a/kernel/fork.c b/kernel/fork.c
index 61a2ac850faf0..892940ea52958 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2127,6 +2127,7 @@ __latent_entropy struct task_struct *copy_process(
p->blocked_on_state = BO_RUNNABLE;
p->blocked_on = NULL; /* not blocked yet */
p->blocked_donor = NULL; /* nobody is boosting p yet */
+ INIT_LIST_HEAD(&p->migration_node);
#ifdef CONFIG_BCACHE
p->sequential_io = 0;
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2c3a4b9518927..c1d813a9cde96 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6741,6 +6741,7 @@ static void proxy_migrate_task(struct rq *rq, struct rq_flags *rf,
struct task_struct *p, int target_cpu)
{
struct rq *target_rq = cpu_rq(target_cpu);
+ LIST_HEAD(migrate_list);
lockdep_assert_rq_held(rq);
@@ -6768,19 +6769,27 @@ static void proxy_migrate_task(struct rq *rq, struct rq_flags *rf,
rq_set_donor(rq, rq->idle);
set_next_task(rq, rq->idle);
- WARN_ON(p == rq->curr);
-
- deactivate_task(rq, p, 0);
- proxy_set_task_cpu(p, target_cpu);
-
+ for (; p; p = p->blocked_donor) {
+ WARN_ON(p == rq->curr);
+ deactivate_task(rq, p, 0);
+ proxy_set_task_cpu(p, target_cpu);
+ /*
+ * We can abuse blocked_node to migrate the thing,
+ * because @p was still on the rq.
+ */
+ list_add(&p->migration_node, &migrate_list);
+ }
zap_balance_callbacks(rq);
rq_unpin_lock(rq, rf);
raw_spin_rq_unlock(rq);
raw_spin_rq_lock(target_rq);
+ while (!list_empty(&migrate_list)) {
+ p = list_first_entry(&migrate_list, struct task_struct, migration_node);
+ list_del_init(&p->migration_node);
- activate_task(target_rq, p, 0);
- wakeup_preempt(target_rq, p, 0);
-
+ activate_task(target_rq, p, 0);
+ wakeup_preempt(target_rq, p, 0);
+ }
raw_spin_rq_unlock(target_rq);
raw_spin_rq_lock(rq);
rq_repin_lock(rq, rf);
--
2.50.0.727.gbf7dc18ff4-goog
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