ASoC: Move system_long_wq to system_dfl_long_wq

Marco Crivellari <marco.crivellari@suse.com> says:

Currently the code uses the per-cpu workqueue system_long_wq to schedule
long running works.

Unbound works could benefit from scheduler task placement, to optimize
performance and power consumption. Another good reason to have this unbound,
is the "queue_delayed_work()" function, used to enqueue the work item.
More details on this will follow in the next section.

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

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

~~~ Details about queue_delayed_work ~~~

system_long_wq is a per-cpu workqueue and it is used as a parameter of
queue_delayed_work(). This function schedule an item that it will later
be enqueued (once the timer will fire). __queue_delayed_work() does the job
receiving as "cpu" WORK_CPU_UNBOUND:

    if (housekeeping_enabled(HK_TYPE_TIMER)) {
    //      [....]
    } else {
            if (likely(cpu == WORK_CPU_UNBOUND))
                    add_timer_global(timer);
            else
                    add_timer_on(timer, cpu);
    }

The timer is global, so can fire everywhere, and the work item will be
enqueued where the timer fired.

Since the workqueue work doesn't rely on per-cpu variables, there is no
obvious reason that justify the use of a per-cpu workqueue. So change the
workqueue with the new system_dfl_long_wq, so that the used workqueue is
now unbound and can benefit from scheduler task placement.

1 files changed, 4 insertions, 2 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index ab6cb70ca1a5..6177624539b3 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -534,8 +534,10 @@ alloc_workqueue_noprof(const char *fmt, unsigned int flags, int max_active, ...)
  * Pointer to the allocated workqueue on success, %NULL on failure.
  */
 __printf(2, 5) struct workqueue_struct *
-devm_alloc_workqueue(struct device *dev, const char *fmt, unsigned int flags,
-		     int max_active, ...);
+devm_alloc_workqueue_noprof(struct device *dev, const char *fmt,
+			    unsigned int flags, int max_active, ...);
+#define devm_alloc_workqueue(...)	\
+	alloc_hooks(devm_alloc_workqueue_noprof(__VA_ARGS__))
 
 #ifdef CONFIG_LOCKDEP
 /**