linux-kernel - Re: [PATCH RESEND] nohz: Affining unpinned timers

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Date:	Tue, 7 Jul 2015 00:49:49 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Vatika Harlalka <vatikaharlalka@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	preeti@...ux.vnet.ibm.com, mingo@...hat.com,
	rafael.j.wysocki@...el.com, schwidefsky@...ibm.com,
	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	cl@...ux.com, cmetcalf@...hip.com, bitbucket@...ine.de
Subject: Re: [PATCH RESEND] nohz: Affining unpinned timers

On Mon, Jul 06, 2015 at 07:18:22PM +0200, Thomas Gleixner wrote:
> On Mon, 6 Jul 2015, Frederic Weisbecker wrote:
> > I hope everybody received the patch because there is a ";" after each address :-)
> > 
> > On Tue, Jun 23, 2015 at 02:01:33PM +0530, Vatika Harlalka wrote:
> > > The problem addressed in this patch is about affining unpinned timers.
> > > Adaptive or Full Dynticks CPUs should not be disturbed by unnecessary
> > > jitter due to firing of such timers on them.
> > > This patch will affine timers to online CPUs which are not Full Dynticks
> > > in FULL_NOHZ configured systems. It will not bring about functional
> > > changes if NOHZ_FULL is not configured, because is_housekeeping_cpu()
> > > always returns true in CONFIG_NO_HZ_FULL=n.
> > > 
> > > Signed-off by: Vatika Harlalka <vatikaharlalka@...il.com>
> > 
> > The patch looks good to me. Peter, Thomas, are you ok with it too?
> 
> By some definition of OK. The overhead of this is growing and growing.
> 
> We really need to make this a pull not a push model.

I'm currently working toward that.
See "[PATCH 0/8] tick/nohz: Tick dependency quick check + cleanups" as a
first step.

Now for this very patch, I don't know how we could make it better. Any
suggestion?

> Thanks,
> 
> 	tglx
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