Re: [GIT PULL] nohz: Adaptively stop the tick, finally

Ingo Molnar
2013-04-24T07:33:06Z

* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> Ingo,
>
> Please pull the latest full dynticks branch that can found at:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> timers/nohz
>
> HEAD: 67826eae8c16dbf00c262be6ec15021bb42f69c4
>
> This handles perf and CPUs that get more than one task and fix posix cpu timers
> handling.
>
> This can finally stop the tick. It boots and doesn't crash, as far as I tested.
>
> Now what's left:
>
> * Kick CPUs' tick when the clock is marked unstable
>
> * Kick CPUs when they extend the RCU grace periods too much by staying in
> the kernel for too long (we are discussing this with Paul).
>
> * sched_class:task_tick(). There are gazillions statistics maintained there.
> It's probably mostly about local and global fairness. May be for other stuff
> too (cgroups, etc...).
>
> * update_cpu_load_active(): again, various stats maintained there
>
> * load balancing (see trigger_load_balance() usually called from the tick).
>
> I hope we can handle these things progressively in the long run.
>
> Thanks.
>
> ---
> Frederic Weisbecker (10):
> posix_timers: Fix pre-condition to stop the tick on full dynticks
> perf: Kick full dynticks CPU if events rotation is needed
> perf: New helper to prevent full dynticks CPUs from stopping tick
> sched: Kick full dynticks CPU that have more than one task enqueued.
> sched: New helper to prevent from stopping the tick in full dynticks
> nohz: Re-evaluate the tick from the scheduler IPI
> nohz: Implement full dynticks kick
> nohz: Prepare to stop the tick on irq exit
> nohz: Re-evaluate the tick for the new task after a context switch
> nohz: Disable the tick when irq resume in full dynticks CPU
>
> include/linux/perf_event.h | 6 +++
> include/linux/sched.h | 6 +++
> include/linux/tick.h | 4 ++
> kernel/events/core.c | 17 +++++++-
> kernel/posix-cpu-timers.c | 6 +-
> kernel/sched/core.c | 24 +++++++++++-
> kernel/sched/sched.h | 11 +++++
> kernel/softirq.c | 19 ++++++--
> kernel/time/tick-sched.c | 95 ++++++++++++++++++++++++++++++++++++++-----
> 9 files changed, 167 insertions(+), 21 deletions(-)

Pulled, thanks Frederic!

One detail: 'make oldconfig' gave me:

Timer tick handling
1. Periodic timer ticks (constant rate, no dynticks) (HZ_PERIODIC) (NEW)
> 2. Idle dynticks system (tickless idle) (NO_HZ_IDLE) (NEW)

I.e. CONFIG_NO_HZ_IDLE is picked by default. The default should really be
CONFIG_HZ_PERIODIC - so that people can easily enable full dynticks but
are not defaulted into it unknowingly.

Thanks,

Ingo