scftorture: Add full-test stutter capability

In virtual environments on systems with hardware assist, inter-processor
interrupts must do very different things based on whether the target
vCPU is running or not.  This commit therefore enables torture-test
stuttering to better test these running/not-running transitions.
Suggested-by: NChris Mason <clm@fb.com>
Signed-off-by: NPaul E. McKenney <paulmck@kernel.org>

kernel/scftorture.c

@@ -59,7 +59,7 @@ torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
 torture_param(int, onoff_interval, 0, "Time between CPU hotplugs (s), 0=disable");
 torture_param(int, shutdown_secs, 0, "Shutdown time (ms), <= zero to disable.");
 torture_param(int, stat_interval, 60, "Number of seconds between stats printk()s.");
-torture_param(int, stutter_cpus, 5, "Number of jiffies to change CPUs under test, 0=disable");
+torture_param(int, stutter, 5, "Number of jiffies to run/halt test, 0=disable");
 torture_param(bool, use_cpus_read_lock, 0, "Use cpus_read_lock() to exclude CPU hotplug.");
 torture_param(int, verbose, 0, "Enable verbose debugging printk()s");
 torture_param(int, weight_resched, -1, "Testing weight for resched_cpu() operations.");
@@ -436,6 +436,7 @@ static int scftorture_invoker(void *arg)
 			was_offline = false;
 		}
 		cond_resched();
+		stutter_wait("scftorture_invoker");
 	} while (!torture_must_stop());
 
 	VERBOSE_SCFTORTOUT("scftorture_invoker %d ended", scfp->cpu);
@@ -448,8 +449,8 @@ static void
 scftorture_print_module_parms(const char *tag)
 {
 	pr_alert(SCFTORT_FLAG
-		 "--- %s:  verbose=%d holdoff=%d longwait=%d nthreads=%d onoff_holdoff=%d onoff_interval=%d shutdown_secs=%d stat_interval=%d stutter_cpus=%d use_cpus_read_lock=%d, weight_resched=%d, weight_single=%d, weight_single_wait=%d, weight_many=%d, weight_many_wait=%d, weight_all=%d, weight_all_wait=%d\n", tag,
-		 verbose, holdoff, longwait, nthreads, onoff_holdoff, onoff_interval, shutdown, stat_interval, stutter_cpus, use_cpus_read_lock, weight_resched, weight_single, weight_single_wait, weight_many, weight_many_wait, weight_all, weight_all_wait);
+		 "--- %s:  verbose=%d holdoff=%d longwait=%d nthreads=%d onoff_holdoff=%d onoff_interval=%d shutdown_secs=%d stat_interval=%d stutter=%d use_cpus_read_lock=%d, weight_resched=%d, weight_single=%d, weight_single_wait=%d, weight_many=%d, weight_many_wait=%d, weight_all=%d, weight_all_wait=%d\n", tag,
+		 verbose, holdoff, longwait, nthreads, onoff_holdoff, onoff_interval, shutdown, stat_interval, stutter, use_cpus_read_lock, weight_resched, weight_single, weight_single_wait, weight_many, weight_many_wait, weight_all, weight_all_wait);
 }
 
 static void scf_cleanup_handler(void *unused)
@@ -558,6 +559,11 @@ static int __init scf_torture_init(void)
 		if (firsterr)
 			goto unwind;
 	}
+	if (stutter > 0) {
+		firsterr = torture_stutter_init(stutter, stutter);
+		if (firsterr)
+			goto unwind;
+	}
 
 	// Worker tasks invoking smp_call_function().
 	if (nthreads < 0)