On Wed, Aug 23, 2023 at 09:50:37AM -0400, Joel Fernandes wrote: > On Tue, Aug 22, 2023 at 3:37 AM Z qiang <qiang.zhang1211@xxxxxxxxx> wrote: > > > > 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. > > I think you have hit a bug. I think the problem is > rcu_torture_disable_rt_throttle() modifies the sysctl knobs, but does > not change def_rt_bandwidth and reinitialize the rt_rq. I think we > need to call sched_rt_do_global() like the sysfs handler does, or > change the sysctl knobs to be earlier in the boot process before the > rt_rq are initialized. > > Or better yet (not sure if it is possible) trigger the sysctl change > via the sysctl layer and let it do the same logic. That would be difficult in built-in rcutorture testing due to the fact that there is not much in the way of userspace. I suppose we could invoke the sysfs handler so as to mock up a userspace access, but that might not be the most robust approach. Another way is to disable preemption in the real-time kthreads. Which might need careful implementation to avoid "scheduling while atomic" and friends. Thanx, Paul
