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Date: Tue, 19 Dec 2023 16:18:18 -0800
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>, Metin Kaya <Metin.Kaya@....com>,
Xuewen Yan <xuewen.yan94@...il.com>, K Prateek Nayak <kprateek.nayak@....com>,
Thomas Gleixner <tglx@...utronix.de>, kernel-team@...roid.com,
Valentin Schneider <valentin.schneider@....com>, "Connor O'Brien" <connoro@...gle.com>,
John Stultz <jstultz@...gle.com>
Subject: [PATCH v7 07/23] locking/mutex: Switch to mutex handoffs for CONFIG_SCHED_PROXY_EXEC
From: Peter Zijlstra <peterz@...radead.org>
Since with SCHED_PROXY_EXEC, we will want to hand off locks to
the tasks we are running on behalf of, switch to using mutex
handoffs.
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: 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: kernel-team@...roid.com
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
[rebased, added comments and changelog]
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
[Fixed rebase conflicts]
[squashed sched: Ensure blocked_on is always guarded by blocked_lock]
Signed-off-by: Valentin Schneider <valentin.schneider@....com>
[fix rebase conflicts, various fixes & tweaks commented inline]
[squashed sched: Use rq->curr vs rq->proxy checks]
Signed-off-by: Connor O'Brien <connoro@...gle.com>
[jstultz: Split out only the very basic initial framework
for proxy logic from a larger patch.]
Signed-off-by: John Stultz <jstultz@...gle.com>
---
v5:
* Split out from core proxy patch
v6:
* Rework to use sched_proxy_exec() instead of #ifdef CONFIG_PROXY_EXEC
v7:
* Avoid disabling optimistic spinning at compile time so booting
with sched_proxy_exec=off matches prior performance
* Add comment in mutex-design.rst as suggested by Metin Kaya
---
Documentation/locking/mutex-design.rst | 3 ++
kernel/locking/mutex.c | 42 +++++++++++++++-----------
2 files changed, 28 insertions(+), 17 deletions(-)
diff --git a/Documentation/locking/mutex-design.rst b/Documentation/locking/mutex-design.rst
index 78540cd7f54b..57a5cb03f409 100644
--- a/Documentation/locking/mutex-design.rst
+++ b/Documentation/locking/mutex-design.rst
@@ -61,6 +61,9 @@ taken, depending on the state of the lock:
waiting to spin on mutex owner, only to go directly to slowpath upon
obtaining the MCS lock.
+ NOTE: Optimistic spinning will be avoided when using proxy execution
+ (SCHED_PROXY_EXEC) as we want to hand the lock off to the task that was
+ boosting the current owner.
(iii) slowpath: last resort, if the lock is still unable to be acquired,
the task is added to the wait-queue and sleeps until woken up by the
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 6084470773f6..11dc5cb7a5a3 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -416,6 +416,9 @@ static __always_inline bool
mutex_optimistic_spin(struct mutex *lock, struct ww_acquire_ctx *ww_ctx,
struct mutex_waiter *waiter)
{
+ if (sched_proxy_exec())
+ return false;
+
if (!waiter) {
/*
* The purpose of the mutex_can_spin_on_owner() function is
@@ -914,26 +917,31 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne
mutex_release(&lock->dep_map, ip);
- /*
- * Release the lock before (potentially) taking the spinlock such that
- * other contenders can get on with things ASAP.
- *
- * Except when HANDOFF, in that case we must not clear the owner field,
- * but instead set it to the top waiter.
- */
- owner = atomic_long_read(&lock->owner);
- for (;;) {
- MUTEX_WARN_ON(__owner_task(owner) != current);
- MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
-
- if (owner & MUTEX_FLAG_HANDOFF)
- break;
+ if (sched_proxy_exec()) {
+ /* Always force HANDOFF for Proxy Exec for now. Revisit. */
+ owner = MUTEX_FLAG_HANDOFF;
+ } else {
+ /*
+ * Release the lock before (potentially) taking the spinlock
+ * such that other contenders can get on with things ASAP.
+ *
+ * Except when HANDOFF, in that case we must not clear the
+ * owner field, but instead set it to the top waiter.
+ */
+ owner = atomic_long_read(&lock->owner);
+ for (;;) {
+ MUTEX_WARN_ON(__owner_task(owner) != current);
+ MUTEX_WARN_ON(owner & MUTEX_FLAG_PICKUP);
- if (atomic_long_try_cmpxchg_release(&lock->owner, &owner, __owner_flags(owner))) {
- if (owner & MUTEX_FLAG_WAITERS)
+ if (owner & MUTEX_FLAG_HANDOFF)
break;
- return;
+ if (atomic_long_try_cmpxchg_release(&lock->owner, &owner,
+ __owner_flags(owner))) {
+ if (owner & MUTEX_FLAG_WAITERS)
+ break;
+ return;
+ }
}
}
--
2.43.0.472.g3155946c3a-goog
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