Re: [tip:x86/urgent] x86/entry/32: Add an ASM_CLAC to entry_SYSENTER_32
From: Ingo Molnar
Date: Thu Feb 25 2016 - 03:41:08 EST
* Mike Galbraith <umgwanakikbuti@xxxxxxxxx> 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
> (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_IDLE is not set
# CONFIG_NO_HZ_FULL_ALL is not set
# CONFIG_NO_HZ_FULL_SYSIDLE is not set
... 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.