The timekeeping duty is currently assigned to the CPU that handles the tick broadcast clock device by the time it is set in one shot mode.
The reason for this is not entirely clear as outlined by Jiri Bohac: https://patchwork.kernel.org/patch/2302951/ One could speculate though that it makes sure only one CPU is woken up to fixup the timekeeping max deferment. But the timekeeper can change anytime after the broadcast CPU becomes idle. So probably we can remove this as in Jiri's patch, but not late in the -rc's. The issue we need to deal with now is that the timekeeping duty must stay handled by the boot CPU in full dynticks mode for now. Otherwise it prevents secondary CPUs from offlining and this breaks suspend/shutdown/reboot/... Long term plan is to make the timekeeper dynamic in full dynticks as well but for now lets prevent that to happen to avoid breakages. Reported-by: Steven Rostedt <[email protected]> Signed-off-by: Frederic Weisbecker <[email protected]> Cc: Jiri Bohac <[email protected]> Cc: Steven Rostedt <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Borislav Petkov <[email protected]> --- kernel/time/tick-broadcast.c | 11 ++++++++--- 1 files changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c index 24938d5..ed3a253 100644 --- a/kernel/time/tick-broadcast.c +++ b/kernel/time/tick-broadcast.c @@ -692,9 +692,14 @@ void tick_broadcast_setup_oneshot(struct clock_event_device *bc) bc->event_handler = tick_handle_oneshot_broadcast; - /* Take the do_timer update */ - if (!tick_nohz_full_cpu(cpu)) - tick_do_timer_cpu = cpu; + /* + * Take the timekeeping duty unless we run in full + * dynticks mode that require the boot CPU to stay + * the timekeeper for now. + */ +#ifndef CONFIG_NO_HZ_FULL + tick_do_timer_cpu = cpu; +#endif /* * We must be careful here. There might be other CPUs -- 1.7.5.4 -- 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/
