On Thu, 2016-02-25 at 09:40 +0100, Ingo Molnar wrote:
> * Mike Galbraith <umgwanakikb...@gmail.com> wrote:
>
> > On Thu, 2016-02-25 at 09:14 +0100, Ingo Molnar wrote:
> >
> > > But but ... 'context tracking' is not really something that a regular
> > > distro
> > > kernel cares about much - it's a nohz-full special AFAICS.
>
> Let me qualify that: with the timer code maintenance hat on I really love all
> nohz
> variants (the deeper the better), but now I have my x86 maintainer hat on,
> and as
> such I'm really annoyed at those nohz folks adding overhead to the syscall
> hot
> path! ;-)
>
> > (psst.. distros are shipping it)
>
> Yeah, indeed, Fedora does - but AFAICS:
>
> fomalhaut:~> grep NO_HZ /boot/config-4.1.13-100.fc21.x86_64
> CONFIG_NO_HZ_COMMON=y
> # CONFIG_NO_HZ_IDLE is not set
> CONFIG_NO_HZ_FULL=y
> # CONFIG_NO_HZ_FULL_ALL is not set
> # CONFIG_NO_HZ_FULL_SYSIDLE is not set
> CONFIG_NO_HZ=y
> CONFIG_RCU_FAST_NO_HZ=y
>
> ... which won't result in actual full-nohz CPUs unless you boot it with a
> special
> boot parameter, right?
Yeah, you have to manually enable it unless you (in a suicidal moment)
enable CONFIG_NO_HZ_FULL_ALL.
> What is the easiest way to query which/how many CPUs are in nohz-full mode
> and do
> context tracking? I somehow thought /proc/timer_* had that info, but that
> does not
> appear to be the case.
/sys/devices/system/cpu/nohz_full
-Mike
