workqueue: make sysfs of unbound kworker cpumask more clever

Some unfriendly component, such as dpdk, write the same mask to
unbound kworker cpumask again and again. Every time it write to
this interface some work is queue to cpu, even though the mask
is same with the original mask.

So, fix it by return success and do nothing if the cpumask is
equal with the old one.

Signed-off-by: Mengen Sun <mengensun@tencent.com>
Signed-off-by: Menglong Dong <imagedong@tencent.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1b3eb1e9531f4ac71ebced9bac749ecea747064f..76988f39ed5ac8afbe9fe32a8fb5655832fc670a 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -5384,9 +5384,6 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
        int ret = -EINVAL;
        cpumask_var_t saved_cpumask;
 
-       if (!zalloc_cpumask_var(&saved_cpumask, GFP_KERNEL))
-               return -ENOMEM;
-
        /*
         * Not excluding isolated cpus on purpose.
         * If the user wishes to include them, we allow that.
@@ -5394,6 +5391,15 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
        cpumask_and(cpumask, cpumask, cpu_possible_mask);
        if (!cpumask_empty(cpumask)) {
                apply_wqattrs_lock();
+               if (cpumask_equal(cpumask, wq_unbound_cpumask)) {
+                       ret = 0;
+                       goto out_unlock;
+               }
+
+               if (!zalloc_cpumask_var(&saved_cpumask, GFP_KERNEL)) {
+                       ret = -ENOMEM;
+                       goto out_unlock;
+               }
 
                /* save the old wq_unbound_cpumask. */
                cpumask_copy(saved_cpumask, wq_unbound_cpumask);
@@ -5406,10 +5412,11 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
                if (ret < 0)
                        cpumask_copy(wq_unbound_cpumask, saved_cpumask);
 
+               free_cpumask_var(saved_cpumask);
+out_unlock:
                apply_wqattrs_unlock();
        }
 
-       free_cpumask_var(saved_cpumask);
        return ret;
 }