Re: Increase priority of a workqueue thread ?

[Con Kolivas <kernel@kolivas.org>]

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On Thu, 20 Oct 2005 23:12, Block Device wrote:
> Hi,
>     I am using a custom workqueue thread in my module. How do I increase
> the priority of the workqueue threads ?
> I've seen that each workqueue contains an array of per-cpu structures
> which has a
> task_struct of the thread on a particular cpu. Since these threads are
> created from keventd
> I think they'll have the same priority as keventd.  Also the per-cpu
> structure is something which is private to the workqueue
> implementation. Directly using it (from my driver) to increase the
> priority of the workqueue doesnt seem correct to me. Is there any
> interface or standard way of changing the priority of a workqueue.

By strange coincidence I was working on a patch to do this. Here's what I have 
so far - I know the code is safe but I don't know if it does as advertised  
yet ;)

Cheers,
Con

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Index: linux-2.6.14-rc4-ck1/include/linux/workqueue.h
===================================================================
--- linux-2.6.14-rc4-ck1.orig/include/linux/workqueue.h	2005-06-18 23:59:46.000000000 +1000
+++ linux-2.6.14-rc4-ck1/include/linux/workqueue.h	2005-10-11 16:03:09.000000000 +1000
@@ -56,6 +56,7 @@ extern struct workqueue_struct *__create
 #define create_singlethread_workqueue(name) __create_workqueue((name), 1)
 
 extern void destroy_workqueue(struct workqueue_struct *wq);
+extern void set_workqueue_nice(struct workqueue_struct *wq, long nice);
 
 extern int FASTCALL(queue_work(struct workqueue_struct *wq, struct work_struct *work));
 extern int FASTCALL(queue_delayed_work(struct workqueue_struct *wq, struct work_struct *work, unsigned long delay));
Index: linux-2.6.14-rc4-ck1/kernel/workqueue.c
===================================================================
--- linux-2.6.14-rc4-ck1.orig/kernel/workqueue.c	2005-10-11 15:56:13.000000000 +1000
+++ linux-2.6.14-rc4-ck1/kernel/workqueue.c	2005-10-11 16:03:09.000000000 +1000
@@ -383,6 +383,26 @@ void destroy_workqueue(struct workqueue_
 	kfree(wq);
 }
 
+void set_workqueue_nice(struct workqueue_struct *wq, long nice)
+{
+	struct task_struct *p;
+	int cpu;
+
+	lock_cpu_hotplug();
+	if (is_single_threaded(wq)) {
+		p = wq->cpu_wq->thread;
+		set_user_nice(p, nice);
+	} else {
+		for_each_online_cpu(cpu) {
+			struct cpu_workqueue_struct *cwq = wq->cpu_wq + cpu;
+	
+			p = cwq->thread;
+			set_user_nice(p, nice);
+		}
+	}
+	unlock_cpu_hotplug();
+}
+
 static struct workqueue_struct *keventd_wq;
 
 int fastcall schedule_work(struct work_struct *work)