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Subjectworkqueue: Only kick a worker after thawed or for an unbound workqueue
Date
In realtime scenario, We do not want to have interference on the
isolated cpu cores. but when invoking alloc_workqueue() for percpu wq
on the housekeeping cpu, it kick a kworker on the isolated cpu.

alloc_workqueue
pwq_adjust_max_active
wake_up_worker

The comment in pwq_adjust_max_active() said:
"Need to kick a worker after thawed or an unbound wq's
max_active is bumped"

So it is unnecessary to kick a kworker for percpu wq's when
alloc_workqueue. this patch only kick a worker after thawed or for an
unbound workqueue.

Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
---
kernel/workqueue.c | 18 +++++++++++++-----
1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index c41c3c17b86a..80f7bbd4889f 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3696,14 +3696,16 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
}

/**
- * pwq_adjust_max_active - update a pwq's max_active to the current setting
+ * pwq_adjust_max_active_and_kick - update a pwq's max_active to the current setting
* @pwq: target pool_workqueue
+ * @force_kick: force to kick a worker
*
* If @pwq isn't freezing, set @pwq->max_active to the associated
* workqueue's saved_max_active and activate delayed work items
* accordingly. If @pwq is freezing, clear @pwq->max_active to zero.
*/
-static void pwq_adjust_max_active(struct pool_workqueue *pwq)
+static void pwq_adjust_max_active_and_kick(struct pool_workqueue *pwq,
+ bool force_kick)
{
struct workqueue_struct *wq = pwq->wq;
bool freezable = wq->flags & WQ_FREEZABLE;
@@ -3733,9 +3735,10 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)

/*
* Need to kick a worker after thawed or an unbound wq's
- * max_active is bumped. It's a slow path. Do it always.
+ * max_active is bumped.
*/
- wake_up_worker(pwq->pool);
+ if (force_kick || (wq->flags & WQ_UNBOUND))
+ wake_up_worker(pwq->pool);
} else {
pwq->max_active = 0;
}
@@ -3743,6 +3746,11 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)
raw_spin_unlock_irqrestore(&pwq->pool->lock, flags);
}

+static void pwq_adjust_max_active(struct pool_workqueue *pwq)
+{
+ pwq_adjust_max_active_and_kick(pwq, false);
+}
+
/* initialize newly alloced @pwq which is associated with @wq and @pool */
static void init_pwq(struct pool_workqueue *pwq, struct workqueue_struct *wq,
struct worker_pool *pool)
@@ -5252,7 +5260,7 @@ void thaw_workqueues(void)
list_for_each_entry(wq, &workqueues, list) {
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq)
- pwq_adjust_max_active(pwq);
+ pwq_adjust_max_active_and_kick(pwq, true);
mutex_unlock(&wq->mutex);
}

--
2.18.4
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