On Tue, Jun 23, 2015 at 11:26:26AM -0700, Paul E. McKenney wrote: > > I really think you're making that expedited nonsense far too accessible. > > This has nothing to do with accessibility and everything to do with > robustness. And with me not becoming the triage center for too many > non-RCU bugs.
But by making it so you're rewarding abuse instead of flagging it :-( > > > And we still need to be able to drop back to synchronize_sched() > > > (AKA wait_rcu_gp(call_rcu_sched) in this case) in case we have both a > > > creative user and a long-running RCU-sched read-side critical section. > > > > No, a long-running RCU-sched read-side is a bug and we should fix that, > > its called a preemption-latency, we don't like those. > > Yes, we should fix them. No, they absolutely must not result in a > meltdown of some unrelated portion of the kernel (like RCU), particularly > if this situation occurs on some system running a production workload > that doesn't happen to care about preemption latency. I still don't see a problem here though; the stop_one_cpu() invocation for the CPU that's suffering its preemption latency will take longer, but so what? How does polling and dropping back to sync_rcu() generate better behaviour than simply waiting for the completion? > > > > + stop_one_cpu(cpu, synchronize_sched_expedited_cpu_stop, > > > > NULL); > > > > > > My thought was to use smp_call_function_single(), and to have the function > > > called recheck dyntick-idle state, avoiding doing a set_tsk_need_resched() > > > if so. > > > > set_tsk_need_resched() is buggy and should not be used. > > OK, what API is used for this purpose? As per exception you (rcu) already have access to resched_cpu(), use that -- if it doesn't do what you need it to, we'll fix it, you're the only consumer of it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
