Unbound workqueue’s kthreads CPU affinity

Is there a way to set CPU affinity for unbound workqueue’s kthreads (those that named kthread/uXX:y)? Something like cpu mask for regular workqueues. Is it a good idea to set it for each kthread using taskset?

Answer

Workqueue subsystem exports sysfs attribute for setting cpu affinity for unbound workers. Code can be found in Workqueue.c:

    5040 static ssize_t wq_unbound_cpumask_store(struct device *dev,
    5041                 struct device_attribute *attr, const char *buf, size_t count)
    5042 {
    5043         cpumask_var_t cpumask;
    5044         int ret;
    5045 
    5046         if (!zalloc_cpumask_var(&cpumask, GFP_KERNEL))
    5047                 return -ENOMEM;
    5048 
    5049         ret = cpumask_parse(buf, cpumask);
    5050         if (!ret)
    5051                 ret = workqueue_set_unbound_cpumask(cpumask);
    5052 
    5053         free_cpumask_var(cpumask);
    5054         return ret ? ret : count;
    5055 }
    5056 
    5057 static struct device_attribute wq_sysfs_cpumask_attr =
    5058         __ATTR(cpumask, 0644, wq_unbound_cpumask_show,
    5059                wq_unbound_cpumask_store)

So any user space application can write to sysfs descriptor to set unbound workqueue cpu mask.

I hope this answers your query.