[PATCH 4.4 02/38] workqueue: Kick a worker based on the actual activation of delayed works

[Greg Kroah-Hartman]

From: Yunfeng Ye <yeyunf...@huawei.com>

[ Upstream commit 01341fbd0d8d4e717fc1231cdffe00343088ce0b ]

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's wq when invoking
alloc_workqueue(). this patch only kick a worker based on the actual
activation of delayed works.

Signed-off-by: Yunfeng Ye <yeyunf...@huawei.com>
Reviewed-by: Lai Jiangshan <jiangshan...@gmail.com>
Signed-off-by: Tejun Heo <t...@kernel.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 kernel/workqueue.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 3fb2d45c0b42f..6b293804cd734 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3361,17 +3361,24 @@ static void pwq_adjust_max_active(struct pool_workqueue 
*pwq)
         * is updated and visible.
         */
        if (!freezable || !workqueue_freezing) {
+               bool kick = false;
+
                pwq->max_active = wq->saved_max_active;
 
                while (!list_empty(&pwq->delayed_works) &&
-                      pwq->nr_active < pwq->max_active)
+                      pwq->nr_active < pwq->max_active) {
                        pwq_activate_first_delayed(pwq);
+                       kick = true;
+               }
 
                /*
                 * 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. In realtime scenarios, always kicking a
+                * worker will cause interference on the isolated cpu cores, so
+                * let's kick iff work items were activated.
                 */
-               wake_up_worker(pwq->pool);
+               if (kick)
+                       wake_up_worker(pwq->pool);
        } else {
                pwq->max_active = 0;
        }
-- 
2.27.0