linux-kernel - Re: irq 16: nobody cared

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Message-ID: <20130422080136.GA7080@gmail.com>
Date:	Mon, 22 Apr 2013 10:01:36 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	tiwai@...e.de, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: irq 16: nobody cared


* Borislav Petkov <bp@...en8.de> wrote:

> From 3c155e9a22036839c09d98a4acbc7e17a5a3783c Mon Sep 17 00:00:00 2001
> From: Borislav Petkov <bp@...e.de>
> Date: Sun, 21 Apr 2013 23:56:15 +0200
> Subject: [PATCH] RCU: Expedite grace periods during suspend/resume
> 
> Paul says CONFIG_RCU_FAST_NO_HZ can increase grace-period durations by a
> factor of four. This, in turn, can change timings during suspend and can
> delay interrupts handling, leading to "IRQ XX: nobody cared" splats and
> the machine disabling those interrupt lines for no sensible reason.
> 
> Thus, we want to temporarily switch to expedited grace periods when
> suspending the box and return to normal settings when resuming. This
> patch does exactly that.

Hm, this really smells like a workaround: treating the symptom, not the 
cause.

How can an increase in grace-periods break drivers and suspend? Do we 
understand exactly what happens there? If we do, can we fix that instead 
of tweaking the RCU timeouts?

Thanks,

	Ingo
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