* Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> [170718 10:00]: > 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(). OK sure I'll take a look at some point. Thanks, Tony -- 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
