linux-kernel - Re: nohz: Warn if the machine can not perform nohz

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Date:	Tue, 16 Jul 2013 03:03:46 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Dave Jones <davej@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	rostedt@...dmis.org
Subject: Re: nohz: Warn if the machine can not perform nohz_full

On Mon, Jul 15, 2013 at 01:38:48PM -0400, Dave Jones wrote:
> On Mon, Jul 15, 2013 at 01:24:23PM -0400, Dave Jones wrote:
>  > On Mon, Jul 15, 2013 at 07:18:02PM +0200, Frederic Weisbecker wrote:
>  >  
>  >  > > So I guess you guys never want this to be enabled on distro kernels ?
>  >  > > If that's the case, can you add something to that effect in Kconfig ?
>  >  > 
>  >  > I believe we want it to be enabled on distros in the long term. But right now it would
>  >  > be a bad idea until the off case (nohz_full= parameter empty) is carefully optimized.
>  >  > I'm currently working on that.
>  >  > 
>  >  > Now for the unstable tsc, which is what it's about on the above code block, we need
>  >  > the tick to be there to leverage the sched clock madness. May be there could be some
>  >  > other solution that could work along full dynticks but for now we chose the easy path.
>  >  > 
>  >  > Are broken TSCs that common?
>  >  
>  > I just hit one apparently.  http://paste.fedoraproject.org/25421/73907845/raw/
>  > That's a fairly recent Atom board, so I suspect it's not uncommon on that platform.
> 
> And here's a Core Duo from circa 2008.
> http://paste.fedoraproject.org/25429/13739098/raw
> 
> Two for two so far. I get the feeling you guys are going to get a ton of these reports.

Definetly, so it comforts me on the fact we need to remove the warning, which may be
interpreted as the symptom of a bug to report while it's not.

We need to warn the user but through another way.
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