On 18 March 2013 20:53, Viresh Kumar [off-list ref] wrote:

queue_work() queues work on current cpu. This may wake up an idle CPU, which is
actually not required.

Some of these works can be processed by any CPU and so we must select a non-idle
CPU here. The initial idea was to modify implementation of queue_work(), but
that may end up breaking lots of kernel code that would be a nightmare to debug.

So, we finalized to adding new workqueue interfaces, for works that don't depend
on a cpu to execute them.

Fixup:

commit 6e5b6fac3353f5e4e5490931b3eb6d3fd7864ca0
Author: Viresh Kumar [off-list ref]
Date:   Tue Mar 19 10:34:20 2013 +0530

    fixup! workqueue: Add helpers to schedule work on any cpu
---
 kernel/workqueue.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index cf9c570..68daf50 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c

@@ -1242,7 +1242,7 @@ retry:
        if (!(wq->flags & WQ_UNBOUND)) {
                if (cpu == WORK_CPU_UNBOUND) {
                        if (on_any_cpu)
-                               cpu = sched_select_cpu(0);
+                               cpu = sched_select_non_idle_cpu(0);
                        else
                                cpu = raw_smp_processor_id();
                }