Hi Thomas, Peter, and Jason,
When I enable CONFIG_PREEMPT_RT_FULL and CONFIG_NO_HZ_FULL
in Linux Kernel v4.1.12-rt12, I find the tick on the nohz_full cpu never stops.
Whenever the nohz_full cpu wants to stop its tick, it would use
get_next_timer_interrupt() to get the time of next timer and check
whether this time is more than one jiffy after current time.
However, get_next_timer_interrupt() always returns now+1 in PREEMPT_RT
and this cpu has no chance of stopping its tick. Please reference
kernel/time/timer.c: get_next_timer_interrupt().
#ifdef CONFIG_PREEMPT_RT_FULL
/*
* On PREEMPT_RT we cannot sleep here. As a result we can't take
* the base lock to check when the next timer is pending and so
* we assume the next jiffy.
*/
return now + 1;
#endif
Does this mean it is a restriction on the current development of PREEMPT_RT?
Thanks,
- Kang
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