On Wed, 2016-10-26 at 12:49 +0200, Thomas Gleixner wrote:

On Thu, 20 Oct 2016, Tim Chen wrote:

quoted

+static int sched_itmt_update_handler(struct ctl_table *table, int write,
+			      void __user *buffer, size_t *lenp, loff_t *ppos)

Please align the arguments proper

static int
sched_itmt_update_handler(struct ctl_table *table, int write,
			  void __user *buffer, size_t *lenp, loff_t *ppos)

Okay.

quoted

+{
+	int ret;
+	unsigned int old_sysctl;

	unsigned int old_sysctl;
	int ret;

Please. It's way simpler to read.

Sure.

quoted

-void sched_set_itmt_support(void)
+int sched_set_itmt_support(void)
 {
 	mutex_lock(&itmt_update_mutex);
 
+	if (sched_itmt_capable) {
+		mutex_unlock(&itmt_update_mutex);
+		return 0;
+	}
+
+	itmt_sysctl_header = register_sysctl_table(itmt_root_table);
+	if (!itmt_sysctl_header) {
+		mutex_unlock(&itmt_update_mutex);
+		return -ENOMEM;
+	}
+
 	sched_itmt_capable = true;
 
+	/*
+	 * ITMT capability automatically enables ITMT
+	 * scheduling for small systems (single node).
+	 */
+	if (topology_num_packages() == 1)
+		sysctl_sched_itmt_enabled = 1;

I really hate this. This is policy and the kernel should not impose
policy. Why would I like to have this enforced on my single socket XEON
server?

quoted

+	if (sysctl_sched_itmt_enabled) {

Why would sysctl_sched_itmt_enabled be true at this point, aside of the
above policy imposement?

That's true, it will only be enabled for the above case.  I can merge
it into the if check above.


Tim