sched,tracing: Convert to sched_set_fifo()

One module user of sched_setscheduler() was overlooked and is
obviously causing build failures.

Convert ring_buffer_benchmark to use sched_set_fifo_low() when fifo==1
and sched_set_fifo() when fifo==2. This is a bit of an abuse, but it
makes the thing 'work' again.

Specifically, it enables all combinations that were previously
possible:

  producer higher than consumer
  consumer higher than producer

Fixes: 616d91b ("sched: Remove sched_setscheduler*() EXPORTs")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lkml.kernel.org/r/20200720214918.GM5523@worktop.programming.kicks-ass.net

Author: Peter Zijlstra

kernel/trace/ring_buffer_benchmark.c

@@ -45,8 +45,8 @@ MODULE_PARM_DESC(write_iteration, "# of writes between timestamp readings");
 static int producer_nice = MAX_NICE;
 static int consumer_nice = MAX_NICE;
 
-static int producer_fifo = -1;
-static int consumer_fifo = -1;
+static int producer_fifo;
+static int consumer_fifo;
 
 module_param(producer_nice, int, 0644);
 MODULE_PARM_DESC(producer_nice, "nice prio for producer");
@@ -55,10 +55,10 @@ module_param(consumer_nice, int, 0644);
 MODULE_PARM_DESC(consumer_nice, "nice prio for consumer");
 
 module_param(producer_fifo, int, 0644);
-MODULE_PARM_DESC(producer_fifo, "fifo prio for producer");
+MODULE_PARM_DESC(producer_fifo, "use fifo for producer: 0 - disabled, 1 - low prio, 2 - fifo");
 
 module_param(consumer_fifo, int, 0644);
-MODULE_PARM_DESC(consumer_fifo, "fifo prio for consumer");
+MODULE_PARM_DESC(consumer_fifo, "use fifo for consumer: 0 - disabled, 1 - low prio, 2 - fifo");
 
 static int read_events;
 
@@ -303,22 +303,22 @@ static void ring_buffer_producer(void)
 		trace_printk("ERROR!\n");
 
 	if (!disable_reader) {
-		if (consumer_fifo < 0)
+		if (consumer_fifo)
+			trace_printk("Running Consumer at SCHED_FIFO %s\n",
+				     consumer_fifo == 1 ? "low" : "high");
+		else
 			trace_printk("Running Consumer at nice: %d\n",
 				     consumer_nice);
-		else
-			trace_printk("Running Consumer at SCHED_FIFO %d\n",
-				     consumer_fifo);
 	}
-	if (producer_fifo < 0)
+	if (producer_fifo)
+		trace_printk("Running Producer at SCHED_FIFO %s\n",
+			     producer_fifo == 1 ? "low" : "high");
+	else
 		trace_printk("Running Producer at nice: %d\n",
 			     producer_nice);
-	else
-		trace_printk("Running Producer at SCHED_FIFO %d\n",
-			     producer_fifo);
 
 	/* Let the user know that the test is running at low priority */
-	if (producer_fifo < 0 && consumer_fifo < 0 &&
+	if (!producer_fifo && !consumer_fifo &&
 	    producer_nice == MAX_NICE && consumer_nice == MAX_NICE)
 		trace_printk("WARNING!!! This test is running at lowest priority.\n");
 
@@ -455,21 +455,19 @@ static int __init ring_buffer_benchmark_init(void)
 	 * Run them as low-prio background tasks by default:
 	 */
 	if (!disable_reader) {
-		if (consumer_fifo >= 0) {
-			struct sched_param param = {
-				.sched_priority = consumer_fifo
-			};
-			sched_setscheduler(consumer, SCHED_FIFO, &param);
-		} else
+		if (consumer_fifo >= 2)
+			sched_set_fifo(consumer);
+		else if (consumer_fifo == 1)
+			sched_set_fifo_low(consumer);
+		else
 			set_user_nice(consumer, consumer_nice);
 	}
 
-	if (producer_fifo >= 0) {
-		struct sched_param param = {
-			.sched_priority = producer_fifo
-		};
-		sched_setscheduler(producer, SCHED_FIFO, &param);
-	} else
+	if (producer_fifo >= 2)
+		sched_set_fifo(producer);
+	else if (producer_fifo == 1)
+		sched_set_fifo_low(producer);
+	else
 		set_user_nice(producer, producer_nice);
 
 	return 0;