[PATCH net-next v5 4/6] net: thunderbolt: Move long delayed work on system_dfl_long_wq

[Marco Crivellari]

Currently the code enqueues the login_work delayed work using
queue_delayed_work(), on system_long_wq. This workqueue should be used
when long works are expected and it is a per-cpu workqueue.

queue_delayed_work() ends up calling __queue_delayed_work(), which, for
a non-zero delay, sets a global timer that could fire anywhere, enqueuing
the work where the timer fired. With a zero delay, as in
tbnet_handle_packet(), no timer is armed and the work is enqueued
directly on the local CPU, i.e. the CPU that handled the TBIP_LOGIN
packet.

Unbound works could benefit from scheduler task placement, to optimize
performance and power consumption. Long work shouldn't stick to a single
CPU.

Recently, a new unbound workqueue specific for long running work has
been added:

    c116737e972e ("workqueue: Add system_dfl_long_wq for long unbound works")

Since login_work doesn't rely on per-cpu variables, there is no obvious
reason that justify the use of a per-cpu workqueue. So change
system_long_wq with system_dfl_long_wq for login_work, so that the work
may benefit from scheduler task placement.

Cc: Mika Westerberg <westeri@xxxxxxxxxx>
Cc: Yehezkel Bernat <YehezkelShB@xxxxxxxxx>
Signed-off-by: Marco Crivellari <marco.crivellari@xxxxxxxx>
Acked-by: Mika Westerberg <westeri@xxxxxxxxxx>
---
 drivers/net/thunderbolt/main.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/net/thunderbolt/main.c b/drivers/net/thunderbolt/main.c
index cf51b9c39f4e..e36a4e1da05d 100644
--- a/drivers/net/thunderbolt/main.c
+++ b/drivers/net/thunderbolt/main.c
@@ -316,7 +316,7 @@ static void start_login(struct tbnet *net)
 	net->login_received = false;
 	mutex_unlock(&net->connection_lock);
 
-	queue_delayed_work(system_long_wq, &net->login_work,
+	queue_delayed_work(system_dfl_long_wq, &net->login_work,
 			   msecs_to_jiffies(1000));
 }
 
@@ -470,7 +470,7 @@ static int tbnet_handle_packet(const void *buf, size_t size, void *data)
 			if (net->login_retries >= TBNET_LOGIN_RETRIES ||
 			    !net->login_sent) {
 				net->login_retries = 0;
-				queue_delayed_work(system_long_wq,
+				queue_delayed_work(system_dfl_long_wq,
 						   &net->login_work, 0);
 			}
 			mutex_unlock(&net->connection_lock);
@@ -723,7 +723,8 @@ static void tbnet_login_work(struct work_struct *work)
 		netdev_dbg(net->dev, "sending login request failed, ret=%d\n",
 			   ret);
 		if (net->login_retries++ < TBNET_LOGIN_RETRIES) {
-			queue_delayed_work(system_long_wq, &net->login_work,
+			queue_delayed_work(system_dfl_long_wq,
+					   &net->login_work,
 					   delay);
 		} else {
 			netdev_info(net->dev, "ThunderboltIP login timed out\n");
-- 
2.56.0