lib/interval_tree_test.c: allow users to limit scope of endpoint

Add a 'max_endpoint' parameter such that users may easily limit the size
of the intervals that are randomly generated.

Link: http://lkml.kernel.org/r/20170518174936.20265-4-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/interval_tree_test.c

@@ -16,6 +16,7 @@ __param(int, perf_loops, 100000, "Number of iterations modifying the tree");
 __param(int, nsearches, 100, "Number of searches to the interval tree");
 __param(int, search_loops, 10000, "Number of iterations searching the tree");
 
+__param(uint, max_endpoint, ~0, "Largest value for the interval's endpoint");
 
 static struct rb_root root = RB_ROOT;
 static struct interval_tree_node *nodes = NULL;
@@ -40,18 +41,20 @@ static void init(void)
 	int i;
 
 	for (i = 0; i < nnodes; i++) {
-		u32 a = prandom_u32_state(&rnd);
-		u32 b = prandom_u32_state(&rnd);
-		if (a <= b) {
-			nodes[i].start = a;
-			nodes[i].last = b;
-		} else {
-			nodes[i].start = b;
-			nodes[i].last = a;
-		}
+		u32 b = (prandom_u32_state(&rnd) >> 4) % max_endpoint;
+		u32 a = (prandom_u32_state(&rnd) >> 4) % b;
+
+		nodes[i].start = a;
+		nodes[i].last = b;
 	}
+
+	/*
+	 * Limit the search scope to what the user defined.
+	 * Otherwise we are merely measuring empty walks,
+	 * which is pointless.
+	 */
 	for (i = 0; i < nsearches; i++)
-		queries[i] = prandom_u32_state(&rnd);
+		queries[i] = (prandom_u32_state(&rnd) >> 4) % max_endpoint;
 }
 
 static int interval_tree_test_init(void)