linux-kernel - Re: [GIT PULL] isolation: 1Hz residual tick offloading v3

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Date:   Fri, 12 Jan 2018 14:18:13 -0500
From:   Luiz Capitulino <lcapitulino@...hat.com>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Lameter <cl@...ux.com>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Mike Galbraith <efault@....de>, Rik van Riel <riel@...hat.com>
Subject: Re: [GIT PULL] isolation: 1Hz residual tick offloading v3

On Thu,  4 Jan 2018 05:25:32 +0100
Frederic Weisbecker <frederic@...nel.org> wrote:

> Ingo,
> 
> Please pull the sched/0hz branch that can be found at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	sched/0hz
> 
> HEAD: 9e932b2cc707209febd130978a5eb9f4a943a3f4
> 
> --
> Now that scheduler_tick() has become resilient towards the absence of
> ticks, current->sched_class->task_tick() is the last piece that needs
> at least 1Hz tick to keep scheduler stats alive.
> 
> This patchset adds a flag to the isolcpus boot option to offload the
> residual 1Hz tick. This way the nohz_full CPUs don't have anymore tick
> (assuming nothing else requires it) as their residual 1Hz tick is
> offloaded to the housekeepers.
> 
> For quick testing, say on CPUs 1-7:
> 
> 	"isolcpus=nohz_offload,domain,1-7"

Sorry for being very late to this series, but I've a few comments to
make (one right now and others in individual patches).

Why are extending isolcpus= given that it's a deprecated interface?
Some people have already moved away from isolcpus= now, but with this
new feature they will be forced back to using it.

What about just adding the new functionality to nohz_full=? That is,
no new options, just make the tick go away since this has always been
what nohz_full= was intended to do?

> 
> Thanks,
> 	Frederic
> ---
> 
> Frederic Weisbecker (5):
>       sched: Rename init_rq_hrtick to hrtick_rq_init
>       sched/isolation: Add scheduler tick offloading interface
>       nohz: Allow to check if remote CPU tick is stopped
>       sched/isolation: Residual 1Hz scheduler tick offload
>       sched/isolation: Document "nohz_offload" flag
> 
> 
>  Documentation/admin-guide/kernel-parameters.txt |  7 +-
>  include/linux/sched/isolation.h                 |  3 +-
>  include/linux/tick.h                            |  2 +
>  kernel/sched/core.c                             | 94 +++++++++++++++++++++++--
>  kernel/sched/isolation.c                        | 10 +++
>  kernel/sched/sched.h                            |  2 +
>  kernel/time/tick-sched.c                        |  7 ++
>  7 files changed, 117 insertions(+), 8 deletions(-)
>