答复: a bug on NO_HZ_FULL_ALL

[Frederic Weisbecker]

On Thu, Nov 14, 2013 at 12:39:24PM +0000, Sunshaojie wrote:
> Do you mean I must select CONFIG_NO_HZ_FULL_SYSIDLE option and merge the patch of "[PATCH] ARM: Support arch_irq_work_raise() via self IPIs"?

Yes you need to select CONFIG_NO_HZ_FULL_SYSIDLE=y. But latest linus tree should be fine
as it contains that patch.

Thanks.

> 
> -----邮件原件-----
> 发件人: Frederic Weisbecker [mailto:fweisbec at gmail.com] 
> 发送时间: 2013年11月14日 19:50
> 收件人: Shaojie Sun
> 抄送: viresh kumar; Vincent Guittot; Alex Shi; Fathi Boudra; Guodong Xu; Amit Kucheria; Chris Redpath; Linaro Kernel; LAK; Kevin Hilman; Sunshaojie
> 主题: Re: a bug on NO_HZ_FULL_ALL
> 
> On Thu, Nov 14, 2013 at 05:54:10PM +0800, Shaojie Sun wrote:
> > No, I think it is a bug.
> > 
> > Because I tested the option with NO_HZ_FULL and without 
> > NO_HZ_FULL_ALL. It had only little interruptes on CPU0 twd.
> > With same code, I added NO_HZ_FULL_ALL option. It had too many 
> > interruptes on CPU0 twd.
> 
> If you select:
> 
>    NO_HZ_FULL=y
>    NO_HZ_FULL_ALL=n
> 
> then you need to pass a nohz_full= cpu range in the boot parameter, otherwise it's simply going to behave like NO_HZ_FULL=n
> 
> OTOH, if you select NO_HZ_FULL_ALL=y, the "nohz_full=" parameter is not needed and all CPUs will be full dynticks except CPU 0 where you should see more tick than usual because it's handling the timekeeping for every other CPUs. Don't forget to select CONFIG_NO_HZ_FULL_SYSIDLE=y or CPU 0 will never shutdown its tick even if the entire system is idle.