rcutorture: Can not Disable RT throttling

[Z qiang]

When running build-in rcutorture tests in 6.5.0-rc4-rt, and found that,
although the value of /proc/sys/kernel/sched_rt_runtime_us is -1,

cat /sys/kernel/debug/sched/debug
....
rt_rq[6]:
  .rt_nr_running                 : 4
  .rt_nr_migratory               : 0
  .rt_throttled                  : 0
  .rt_time                       : 0.000000
  .rt_runtime                    : 950.000000

but the rt_runtime still is 950.000000.
set sysctl_sched_rt_runtime in rcu_torture_disable_rt_throttle()
does not disable rt-throttling.

Currently I'm testing this way to disable rt-throttling:

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 338cd150973f..bb9fee51a476 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -22,7 +22,7 @@ unsigned int sysctl_sched_rt_period = 1000000;
  * part of the period that we allow rt tasks to run in us.
  * default: 0.95s
  */
-int sysctl_sched_rt_runtime = 950000;
+int sysctl_sched_rt_runtime = IS_BUILTIN(CONFIG_RCU_TORTURE_TEST) ?
-1 : 950000;

 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC / HZ) * RR_TIMESLICE;


Is there a better way to solve it?

Thanks
Zqiang