On Mon, Jul 17, 2017 at 10:41:38PM -0700, Tony Lindgren wrote: > * Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> [170717 05:40]: > > On Sun, Jul 16, 2017 at 11:08:07PM -0700, Tony Lindgren wrote: > > > * Alex Shi <alex.shi@xxxxxxxxxx> [170716 16:25]: > > > > I reused the rcu_irq_enter_irqson() from RCU_NONIDLE to avoid this issue. > > > > It works fine. > > > > > > > > Tony, Could you like to give a tested-by if this patch works for you. > > > > > > Yeah that keeps things booting for me with no splats so: > > > > > > Tested-by: Tony Lindgren <tony@xxxxxxxxxxx> > > > > > > In general, it seems we're missing the knowledge in Linux kernel > > > of when the entire system is idle. Right now it seems that only > > > cpuidle_coupled knows that? > > > > > > We could probably simplify things by adding some PM state for > > > entire system idle. Then cpuidle code and timer code could use > > > that to test when it's safe to do whatever the SoC needs to do > > > to enter deeper power states. > > > > > > If we already have something like that, please do let me know :) > > > > Well, we used to have CONFIG_NO_HZ_FULL_SYSIDLE, which detected > > full-system idle lazily so as to avoid scalability bottlenecks. > > https://lwn.net/Articles/558284/ > > > > No one was using it, so I removed it last merge window. The > > patch that removed it is at sysidle.2017.05.11a, which can > > probably still be reverted cleanly. Or just use v4.11 or earlier. > > OK thanks for the pointer, for reference that commit is > fe5ac724d81a ("rcu: Remove nohz_full full-system-idle state > machine"). > > For a potential user, I think we could use it for example in > cpuidle_enter_state_coupled() + omap_enter_idle_coupled() where > we try to figure out if the system is fully idle before calling > tick_broadcast_enter(). Would you be willing to prototype your usage on v4.12? It still has NO_HZ_FULL_SYSIDLE. You have to enable NO_HZ_FULL in order to enable NO_HZ_FULL_SYSIDLE at the moment. Either way, here is the important bit for usage: bool rcu_sys_is_idle(void); void rcu_sysidle_force_exit(void); The rcu_sys_is_idle() function returns true if all CPUs other than the time-keeping CPU (that is, tick_do_timer_cpu, which is usually CPU 0) are in their idle loop. Of course, if you invoke rcu_sys_is_idle() from any CPU other than the time-keeping CPU, you will automatically get a return value of false. RCU's idle-exit code already sets state appropriately, but if there is some other circumstance where you need to force the state machine out of all-CPUs-idle state, you can call rcu_sysidle_force_exit(). Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
