Re: CONFIG_NO_HZ_FULL = y but still have arch-timer on isolation CPUs

[Ivan Jiang via Xenomai]

Dear Hongzhan：

        My kernel is 4.19.165, indeed remove xenomai, the phenomenon is the 
same.
        Maybe it’s a bug in this kernel, and how can I trace this bug if it is 
fixed in some patch?
        Thank you.

Ivan

在 2022/3/16 11:30，“Chen, Hongzhan”<hongzhan.c...@intel.com> 写入:

    Hi Ivan

    Hope that what discussed in  
https://stackoverflow.com/questions/60322119/completely-eliminating-the-timer-tick-in-modern-linux-5-0
 may help you.
    Seems that there need  do more settings for kernel parameters per your 
requirement but I have not tried myself.  When you remove Xenomai,  the 
phenomenon is the same?

    Regards

    Hongzhan Chen

    -----Original Message-----
    From: Xenomai <xenomai-boun...@xenomai.org> On Behalf Of Ivan Jiang via 
Xenomai
    Sent: Tuesday, March 15, 2022 12:01 PM
    To: xenomai@xenomai.org
    Subject: CONFIG_NO_HZ_FULL = y but still have arch-timer on isolation CPUs

    Dear Guys:



           I’ve set the configs like this

           CONFIG_NO_HZ_FULL = y

    CONFIG_RCU_NOCB_CPU=y

    CONFIG_PREEMPT=y

    CONFIG_CPU_IDLE=n

    CONFIG_ARM_CPUIDLE=n

    CONFIG_CPU_FREQ=n 

    And setenv isolcpus=1 xenomai.supported_cpus=0x02 nohz_full=1  
irqaffinity=0   rcu_nocbs=1

    The CPU is Cortex-A55 Dual core and I use CPU 0 as Linux CPU and CPU1 for 
isolation core.

    But cat /proc/interrupts still the arch_timers are increasing the same time 
on both CPUs.

    Seems NO_HZ_FULL = y has no effect.

    The boot log as below:

    [    0.000000] rcu: Preemptible hierarchical RCU implementation.

    [    0.000000] rcu:     RCU dyntick-idle grace-period acceleration is 
enabled.

    [    0.000000] rcu:     RCU restricting CPUs from NR_CPUS=8 to nr_cpu_ids=2.

    [    0.000000] rcu:     RCU priority boosting: priority 1 delay 500 ms.

    [    0.000000]  Tasks RCU enabled.

    [    0.000000] rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=2

    [    0.000000] NR_IRQS: 64, nr_irqs: 64, preallocated irqs: 0

    [    0.000000] GICv3: Distributor has no Range Selector support

    [    0.000000] GICv3: no VLPI support, no direct LPI support

    [    0.000000] GICv3: CPU0: found redistributor 0 region 
0:0x0000000011940000

    [    0.000000] NO_HZ: Full dynticks CPUs: 1.

    [    0.000000] rcu:     Offload RCU callbacks from CPUs: 1.

    [    0.000000] arch_timer: cp15 timer(s) running at 24.00MHz (virt).

    Please help me to analysis this situation.



    Very appreciate,

    Chen.