Messages in this thread Patch in this message | | | Date | Tue, 19 Dec 2023 16:18:26 -0800 | Subject | [PATCH v7 15/23] sched: Add blocked_donor link to task for smarter mutex handoffs | From | John Stultz <> |
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From: Peter Zijlstra <peterz@infradead.org>
Add link to the task this task is proxying for, and use it so we do intelligent hand-off of the owned mutex to the task we're running on behalf.
Cc: Joel Fernandes <joelaf@google.com> Cc: Qais Yousef <qyousef@google.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Valentin Schneider <vschneid@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ben Segall <bsegall@google.com> Cc: Zimuzo Ezeozue <zezeozue@google.com> Cc: Youssef Esmat <youssefesmat@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Will Deacon <will@kernel.org> Cc: Waiman Long <longman@redhat.com> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Metin Kaya <Metin.Kaya@arm.com> Cc: Xuewen Yan <xuewen.yan94@gmail.com> Cc: K Prateek Nayak <kprateek.nayak@amd.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-team@android.com Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> Signed-off-by: Connor O'Brien <connoro@google.com> [jstultz: This patch was split out from larger proxy patch] Signed-off-by: John Stultz <jstultz@google.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 v7: * Use more descriptive term then "us" in comments, as suggested by Metin Kaya. * Minor typo fixup from Metin Kaya * Reworked proxied variable to prev_not_proxied to simplify usage --- 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 880af1c3097d..8020e224e057 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1157,6 +1157,7 @@ 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 */ raw_spinlock_t blocked_lock; #ifdef CONFIG_DEBUG_ATOMIC_SLEEP diff --git a/kernel/fork.c b/kernel/fork.c index b3ba3d22d8b2..138fc23cad43 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2459,6 +2459,7 @@ __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 */ #ifdef CONFIG_BCACHE p->sequential_io = 0; p->sequential_io_avg = 0; diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 11dc5cb7a5a3..2711af8c0052 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -910,7 +910,7 @@ 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; @@ -948,7 +948,34 @@ 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 current, and that task was boosting + * current 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_state = BO_WAKING; + 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, @@ -956,7 +983,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne next = waiter->task; - raw_spin_lock(&next->blocked_lock); + raw_spin_lock_nested(&next->blocked_lock, SINGLE_DEPTH_NESTING); debug_mutex_wake_waiter(lock, waiter); WARN_ON(next->blocked_on != lock); next->blocked_on_state = BO_WAKING; @@ -967,6 +994,8 @@ 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 55dc2a3b7e46..e0afa228bc9d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6765,7 +6765,17 @@ proxy_migrate_task(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: * @@ -6897,6 +6907,8 @@ find_proxy_task(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); @@ -6979,6 +6991,7 @@ static void __sched notrace __schedule(unsigned int sched_mode) unsigned long prev_state; struct rq_flags rf; struct rq *rq; + bool prev_not_proxied; int cpu; bool preserve_need_resched = false; @@ -7030,9 +7043,11 @@ static void __sched notrace __schedule(unsigned int sched_mode) switch_count = &prev->nvcsw; } + prev_not_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 = find_proxy_task(rq, next, &rf); if (!next) { @@ -7088,7 +7103,7 @@ 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 (!task_current_selected(rq, next)) + if (prev_not_proxied && next->blocked_donor) proxy_tag_curr(rq, next); rq_unpin_lock(rq, &rf); -- 2.43.0.472.g3155946c3a-goog
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