From fe089f87cccb066e8ad20f49ddf05e95adc1fa8d Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Mon, 7 Aug 2023 15:57:22 -1000
Subject: [PATCH] workqueue: Not all work insertion needs to wake up a worker
insert_work() always tried to wake up a worker; however, the only time it
needs to try to wake up a worker is when a new active work item is queued.
When a work item goes on the inactive list or queueing a flush work item,
there's no reason to try to wake up a worker.
This patch moves the worker wakeup logic out of insert_work() and places it
in the active new work item queueing path in __queue_work().
While at it:
* __queue_work() is dereferencing pwq->pool repeatedly. Add local variable
pool.
* Every caller of insert_work() calls debug_work_activate(). Consolidate the
invocations into insert_work().
* In __queue_work() pool->watchdog_ts update is relocated slightly. This is
to better accommodate future changes.
This makes wakeups more precise and will help the planned change to assign
work items to workers before waking them up. No behavior changes intended.
v2: WARN_ON_ONCE(pool != last_pool) added in __queue_work() to clarify as
suggested by Lai.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
---
kernel/workqueue.c | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 20722de9937a0..1332bd545b929 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1542,7 +1542,7 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
struct list_head *head, unsigned int extra_flags)
{
- struct worker_pool *pool = pwq->pool;
+ debug_work_activate(work);
/* record the work call stack in order to print it in KASAN reports */
kasan_record_aux_stack_noalloc(work);
@@ -1551,9 +1551,6 @@ static void insert_work(struct pool_workqueue *pwq, struct work_struct *work,
set_work_pwq(work, pwq, extra_flags);
list_add_tail(&work->entry, head);
get_pwq(pwq);
-
- if (__need_more_worker(pool))
- wake_up_worker(pool);
}
/*
@@ -1607,8 +1604,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
struct work_struct *work)
{
struct pool_workqueue *pwq;
- struct worker_pool *last_pool;
- struct list_head *worklist;
+ struct worker_pool *last_pool, *pool;
unsigned int work_flags;
unsigned int req_cpu = cpu;
@@ -1642,13 +1638,15 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
pwq = per_cpu_ptr(wq->cpu_pwqs, cpu);
}
+ pool = pwq->pool;
+
/*
* If @work was previously on a different pool, it might still be
* running there, in which case the work needs to be queued on that
* pool to guarantee non-reentrancy.
*/
last_pool = get_work_pool(work);
- if (last_pool && last_pool != pwq->pool) {
+ if (last_pool && last_pool != pool) {
struct worker *worker;
raw_spin_lock(&last_pool->lock);
@@ -1657,13 +1655,15 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
if (worker && worker->current_pwq->wq == wq) {
pwq = worker->current_pwq;
+ pool = pwq->pool;
+ WARN_ON_ONCE(pool != last_pool);
} else {
/* meh... not running there, queue here */
raw_spin_unlock(&last_pool->lock);
- raw_spin_lock(&pwq->pool->lock);
+ raw_spin_lock(&pool->lock);
}
} else {
- raw_spin_lock(&pwq->pool->lock);
+ raw_spin_lock(&pool->lock);
}
/*
@@ -1676,7 +1676,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
*/
if (unlikely(!pwq->refcnt)) {
if (wq->flags & WQ_UNBOUND) {
- raw_spin_unlock(&pwq->pool->lock);
+ raw_spin_unlock(&pool->lock);
cpu_relax();
goto retry;
}
@@ -1695,21 +1695,22 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
work_flags = work_color_to_flags(pwq->work_color);
if (likely(pwq->nr_active < pwq->max_active)) {
+ if (list_empty(&pool->worklist))
+ pool->watchdog_ts = jiffies;
+
trace_workqueue_activate_work(work);
pwq->nr_active++;
- worklist = &pwq->pool->worklist;
- if (list_empty(worklist))
- pwq->pool->watchdog_ts = jiffies;
+ insert_work(pwq, work, &pool->worklist, work_flags);
+
+ if (__need_more_worker(pool))
+ wake_up_worker(pool);
} else {
work_flags |= WORK_STRUCT_INACTIVE;
- worklist = &pwq->inactive_works;
+ insert_work(pwq, work, &pwq->inactive_works, work_flags);
}
- debug_work_activate(work);
- insert_work(pwq, work, worklist, work_flags);
-
out:
- raw_spin_unlock(&pwq->pool->lock);
+ raw_spin_unlock(&pool->lock);
rcu_read_unlock();
}
@@ -3012,7 +3013,6 @@ static void insert_wq_barrier(struct pool_workqueue *pwq,
pwq->nr_in_flight[work_color]++;
work_flags |= work_color_to_flags(work_color);
- debug_work_activate(&barr->work);
insert_work(pwq, &barr->work, head, work_flags);
}
--
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