Hello,
I was looking at the arch/arm/process.c:cpu_die, I was wondering why we
do not exit from NOHZ for a hotplugged/offline cpu?
If I understand correctly an offlined cpu too will enter
NOHz(tick_nohz_idle_enter) and update the idle_entrytime. The cpu will die
and it will reenter the idle thread and update idle_entrytime onces it
comes back online and only then it will exit NOHz, but time spent in sleep
idle_sleeptime will be wrongly calculated.
void cpu_idle(void)
{
.....
/* endless idle loop with no priority at all */
while (1) {
idle_notifier_call_chain(IDLE_START);
tick_nohz_idle_enter();--> Offline CPU entering NOHZ
rcu_idle_enter();
while (!need_resched()) {
#ifdef CONFIG_HOTPLUG_CPU
if (cpu_is_offline(smp_processor_id()))
cpu_die(); ---> CPU becomes offline and re-enter the idle thread without
exiting from NOHZ,
#endif
...
}
Is it a good idea to exit from NOHZ before cpu_die() or it could be
achieved in some other way? Please provide your
comments.
--
Thanks & Regards,
Taniya Das.
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation.
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