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Date: Tue, 13 Dec 2016 16:49:10 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
cc: LKML <linux-kernel@vger.kernel.org>, x86@kernel.org,
        Borislav Petkov <bp@alien8.de>,
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        Roland Scheidegger <rscheidegger_lists@hispeed.ch>,
        Kevin Stanton <kevin.b.stanton@intel.com>,
        Allen Hung <allen_hung@dell.com>
Subject: Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >=
 zero
In-Reply-To: <20161213134358.GV3207@twins.programming.kicks-ass.net>
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References: <20161213131115.764824574@linutronix.de> <20161213131211.397588033@linutronix.de> <20161213134358.GV3207@twins.programming.kicks-ass.net>
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On Tue, 13 Dec 2016, Peter Zijlstra wrote:
> On Tue, Dec 13, 2016 at 01:14:17PM -0000, Thomas Gleixner wrote:
> > @@ -429,8 +447,13 @@ void check_tsc_sync_target(void)
> >  	 * that the warp is not longer detectable when the observed warp
> >  	 * value is used. In the worst case the adjustment needs to go
> >  	 * through a 3rd run for fine tuning.
> > +	 *
> > +	 * But we must make sure that the value doesn't become negative
> > +	 * otherwise TSC deadline timer will create an interrupt storm.
> >  	 */
> >  	cur->adjusted += cur_max_warp;
> > +	if (cur->adjusted < 0)
> > +		cur->adjusted = 0;
> >  
> 
> So depending on how horrid we want to make this we could work around
> this by increasing the ADJUST of the other CPUs by the amount we're
> negative.

That means to increase all CPUs in the package of the other CPU by that
amount ....

> But yes, yuck.

Indeed.

	tglx