linux-kernel - Re: [GIT PULL v2] nohz: Move nohz kick out of scheduler IPI

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Message-ID: <20140416073708.GA5636@gmail.com>
Date:	Wed, 16 Apr 2014 09:37:08 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jens Axboe <axboe@...com>, Kevin Hilman <khilman@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [GIT PULL v2] nohz: Move nohz kick out of scheduler IPI


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

> Ingo, Thomas,
> 
> Please pull the timers/nohz-ipi-for-tip-v3 branch that can be found at:
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	timers/nohz-ipi-for-tip-v3
> 
> It is based on 7a48837732f87a574ee3e1855927dc250117f565 
> ("Merge branch 'for-3.15/core' of git://git.kernel.dk/linux-block")
> due to dependencies on the block tree containing IPI core changes.
> 
> This v2 addresses Paul review and add his reviewed-by tags.
> 
> I'm trying to get these 2 patches in before the merge window ends
> otherwise we'll have to do tricky branch split on the next cycle.
> 
> ---
> When a full dynticks CPU runs in single task mode then a new task gets
> enqueued, we notify it through an IPI such that it restarts its tick.
> 
> The IPI used here is the scheduler IPI. There are a few reasons for that:
> it can be called when interrupts are disabled, it can be called
> concurrently... These convenient properties altogether aren't yet offered
> by the IPI subsystem.
> 
> Meanwhile, bloating that way the scheduler IPI with scheduler unrelated
> code is an abuse of this fast path. We certainly don't want to start a
> big kernel IPI.
> 
> So this patchset adds a small helper to the IPI subsystem that allows
> to queue an IPI from interrupt disabled code while handling concurrent
> callers as well. Eventually the nohz kick gets converted to this new facility.
> 
> Partly inspired by a suggestion from Peter Zijlstra.
> 
> * Patch 1/2 brings the IPI infrastructure to support this
> * Patch 2/2 does the nohz IPI conversion
> 
> 
> Thanks,
> 	Frederic
> ---
> 
> Frederic Weisbecker (2):
>       smp: Non busy-waiting IPI queue
>       nohz: Move full nohz kick to its own IPI
> 
> 
>  include/linux/smp.h      | 11 +++++++++++
>  include/linux/tick.h     |  2 ++
>  kernel/sched/core.c      |  5 +----
>  kernel/sched/sched.h     |  2 +-
>  kernel/smp.c             | 42 ++++++++++++++++++++++++++++++++++++++++++
>  kernel/time/tick-sched.c | 21 +++++++++++++++++++++
>  6 files changed, 78 insertions(+), 5 deletions(-)

Pulled into tip:timers/nohz, thanks a lot Frederic!

	Ingo
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