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Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >= zero

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >= zero
Date 2016-12-13 14:50 +0100
Message-ID <sNVCW-1NI-17@gated-at.bofh.it> (permalink)
References <sNV9U-1DV-7@gated-at.bofh.it> <sNV9U-1DV-27@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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.

But yes, yuck.

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[patch 2/2] x86/tsc: Force TSC_ADJUST register to value >= zero Thomas Gleixner <tglx@linutronix.de> - 2016-12-13 14:20 +0100
  Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >= zero Peter Zijlstra <peterz@infradead.org> - 2016-12-13 14:50 +0100
    Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >=  zero Thomas Gleixner <tglx@linutronix.de> - 2016-12-13 17:00 +0100
  [tip:x86/timers] x86/tsc: Force TSC_ADJUST register to value >=  zero tip-bot for Thomas Gleixner <tipbot@zytor.com> - 2016-12-15 12:00 +0100
  Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >=  zero Thomas Gleixner <tglx@linutronix.de> - 2016-12-16 12:50 +0100
    Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >=  zero Thomas Gleixner <tglx@linutronix.de> - 2016-12-16 13:00 +0100
    Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >= zero Ingo Molnar <mingo@kernel.org> - 2016-12-16 13:10 +0100
    Re: [patch 2/2] x86/tsc: Force TSC_ADJUST register to value >=  zero Thomas Gleixner <tglx@linutronix.de> - 2016-12-16 14:40 +0100

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