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Message-ID: <20231106193524.866104-20-jstultz@google.com>
Date: Mon, 6 Nov 2023 19:35:02 +0000
From: John Stultz <jstultz@...gle.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
Joel Fernandes <joelaf@...gle.com>,
Qais Yousef <qyousef@...gle.com>,
Ingo Molnar <mingo@...hat.com>,
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>,
Youssef Esmat <youssefesmat@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Daniel Bristot de Oliveira <bristot@...hat.com>,
Will Deacon <will@...nel.org>,
Waiman Long <longman@...hat.com>,
Boqun Feng <boqun.feng@...il.com>,
"Paul E . McKenney" <paulmck@...nel.org>, kernel-team@...roid.com,
Valentin Schneider <valentin.schneider@....com>,
"Connor O'Brien" <connoro@...gle.com>,
John Stultz <jstultz@...gle.com>
Subject: [PATCH v6 19/20] sched: Add blocked_donor link to task for smarter
mutex handoffs
From: Peter Zijlstra <peterz@...radead.org>
Add link to the task this task is proxying for, and use it so we
do intellegent hand-off of the owned mutex to the task we're
running on behalf.
Cc: Joel Fernandes <joelaf@...gle.com>
Cc: Qais Yousef <qyousef@...gle.com>
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: Youssef Esmat <youssefesmat@...gle.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Daniel Bristot de Oliveira <bristot@...hat.com>
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: kernel-team@...roid.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
Signed-off-by: Connor O'Brien <connoro@...gle.com>
[jstultz: This patch was split out from larger proxy patch]
Signed-off-by: John Stultz <jstultz@...gle.com>
---
v5:
* Split out from larger proxy patch
v6:
* Moved proxied value from earlier patch to this one where it
is actually used
* Rework logic to check sched_proxy_exec() instead of using ifdefs
* Moved comment change to this patch where it makes sense
---
include/linux/sched.h | 1 +
kernel/fork.c | 1 +
kernel/locking/mutex.c | 35 ++++++++++++++++++++++++++++++++---
kernel/sched/core.c | 19 +++++++++++++++++--
4 files changed, 51 insertions(+), 5 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 47c7095b918a..9bff2f123207 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1145,6 +1145,7 @@ struct task_struct {
struct rt_mutex_waiter *pi_blocked_on;
#endif
+ struct task_struct *blocked_donor; /* task that is boosting us */
struct mutex *blocked_on; /* lock we're blocked on */
bool blocked_on_waking; /* blocked on, but waking */
raw_spinlock_t blocked_lock;
diff --git a/kernel/fork.c b/kernel/fork.c
index 930947bf4569..6604e0472da0 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2456,6 +2456,7 @@ __latent_entropy struct task_struct *copy_process(
lockdep_init_task(p);
#endif
+ p->blocked_donor = NULL; /* nobody is boosting us yet */
p->blocked_on = NULL; /* not blocked yet */
p->blocked_on_waking = false; /* not blocked yet */
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 5394a3c4b5d9..f7187a247482 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -907,7 +907,7 @@ EXPORT_SYMBOL_GPL(ww_mutex_lock_interruptible);
*/
static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigned long ip)
{
- struct task_struct *next = NULL;
+ struct task_struct *donor, *next = NULL;
DEFINE_WAKE_Q(wake_q);
unsigned long owner;
unsigned long flags;
@@ -945,7 +945,34 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
preempt_disable();
raw_spin_lock_irqsave(&lock->wait_lock, flags);
debug_mutex_unlock(lock);
- if (!list_empty(&lock->wait_list)) {
+
+ if (sched_proxy_exec()) {
+ raw_spin_lock(¤t->blocked_lock);
+ /*
+ * If we have a task boosting us, and that task was boosting us through
+ * this lock, hand the lock to that task, as that is the highest
+ * waiter, as selected by the scheduling function.
+ */
+ donor = current->blocked_donor;
+ if (donor) {
+ struct mutex *next_lock;
+
+ raw_spin_lock_nested(&donor->blocked_lock, SINGLE_DEPTH_NESTING);
+ next_lock = get_task_blocked_on(donor);
+ if (next_lock == lock) {
+ next = donor;
+ donor->blocked_on_waking = true;
+ wake_q_add(&wake_q, donor);
+ current->blocked_donor = NULL;
+ }
+ raw_spin_unlock(&donor->blocked_lock);
+ }
+ }
+
+ /*
+ * Failing that, pick any on the wait list.
+ */
+ if (!next && !list_empty(&lock->wait_list)) {
/* get the first entry from the wait-list: */
struct mutex_waiter *waiter =
list_first_entry(&lock->wait_list,
@@ -954,7 +981,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
next = waiter->task;
debug_mutex_wake_waiter(lock, waiter);
- raw_spin_lock(&next->blocked_lock);
+ raw_spin_lock_nested(&next->blocked_lock, SINGLE_DEPTH_NESTING);
WARN_ON(next->blocked_on != lock);
next->blocked_on_waking = true;
raw_spin_unlock(&next->blocked_lock);
@@ -964,6 +991,8 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
if (owner & MUTEX_FLAG_HANDOFF)
__mutex_handoff(lock, next);
+ if (sched_proxy_exec())
+ raw_spin_unlock(¤t->blocked_lock);
raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
wake_up_q(&wake_q);
preempt_enable();
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 760e2753a24c..6ac7a241dacc 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6782,7 +6782,17 @@ static inline bool proxy_return_migration(struct rq *rq, struct rq_flags *rf,
* Find who @next (currently blocked on a mutex) can proxy for.
*
* Follow the blocked-on relation:
- * task->blocked_on -> mutex->owner -> task...
+ *
+ * ,-> task
+ * | | blocked-on
+ * | v
+ * blocked_donor | mutex
+ * | | owner
+ * | v
+ * `-- task
+ *
+ * and set the blocked_donor relation, this latter is used by the mutex
+ * code to find which (blocked) task to hand-off to.
*
* Lock order:
*
@@ -6919,6 +6929,8 @@ proxy(struct rq *rq, struct task_struct *next, struct rq_flags *rf)
*/
raw_spin_unlock(&p->blocked_lock);
raw_spin_unlock(&mutex->wait_lock);
+
+ owner->blocked_donor = p;
}
WARN_ON_ONCE(owner && !owner->on_rq);
@@ -7003,6 +7015,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
unsigned long prev_state;
struct rq_flags rf;
struct rq *rq;
+ bool proxied;
int cpu;
bool preserve_need_resched = false;
@@ -7053,9 +7066,11 @@ static void __sched notrace __schedule(unsigned int sched_mode)
switch_count = &prev->nvcsw;
}
+ proxied = !!prev->blocked_donor;
pick_again:
next = pick_next_task(rq, rq_selected(rq), &rf);
rq_set_selected(rq, next);
+ next->blocked_donor = NULL;
if (unlikely(task_is_blocked(next))) {
next = proxy(rq, next, &rf);
if (!next) {
@@ -7119,7 +7134,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
rq = context_switch(rq, prev, next, &rf);
} else {
/* In case next was already curr but just got blocked_donor*/
- if (unlikely(!task_current_selected(rq, next)))
+ if (unlikely(!proxied && next->blocked_donor))
proxy_tag_curr(rq, next);
rq->clock_update_flags &= ~(RQCF_ACT_SKIP|RQCF_REQ_SKIP);
--
2.42.0.869.gea05f2083d-goog
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