* Mike Galbraith <[email protected]> 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?
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.
Thanks,
Ingo
