On Sun, Aug 11, 2019 at 09:24:31PM -0400, Joel Fernandes wrote: > On Sun, Aug 11, 2019 at 04:30:24PM -0700, Paul E. McKenney wrote: [snip] > > Next question: Why does rcu_implicit_dynticks_qs() check only for > > tick_nohz_full_cpu() and not also IS_ENABLED(CONFIG_PREEMPT)? After > > all, a nohz_full CPU in a !CONFIG_PREEMPT kernel should be able to > > rely on cond_resched(), right? > > > > Should this change? Why or why not? > > Let me think more about this :) I have an answer in mind but I will think a > bit more about it and responsd :) It should not change. That's because (as somewhat mentioned in the comments), some code paths in the kernel check need_resched() before invoking cond_resched(). So even with PREEMPT=n having the help of cond_resched(), the cond_resched() may actually not even be invoked. So in this case, the resched_cpu() from rcu_implicit_dynticks_qs() does the needful by setting the rescheduling flags on the CPU, so that cond_resched() on those CPUs actually get called. Is that a correct analysis? thanks, - Joel
