linux-kernel - Re: [PATCH] x86/irq: Cure live lock in irq_force_complete

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Message-ID: <alpine.DEB.2.11.1603120926310.3657@nanos>
Date:	Sat, 12 Mar 2016 09:27:28 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Luck, Tony" <tony.luck@...el.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Harry Junior <harryjr@...look.fr>, x86@...nel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Joe Lawrence <joe.lawrence@...atus.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/irq: Cure live lock in irq_force_complete_move()

On Fri, 11 Mar 2016, Luck, Tony wrote:

> With this patch applied my system survives me doing
> several rounds of:
> 
> # echo 0 | tee /sys/devices/system/cpu/cpu*/online
> # echo 1 | tee /sys/devices/system/cpu/cpu*/online
> 
> whereas without the patch the first of those went to
> 
> [152455.129604] NMI watchdog: Watchdog detected hard LOCKUP on cpu 96
> [152455.136943] Kernel panic - not syncing: Hard LOCKUP
> 
> I'm not sure we care to optimize the cpu offline path, but I'll note here
> that taking all (but one) cpus offline took 52 seconds (for a hundred
> and mumble logical cpus).  Bringing them all back is just 4 seconds.

Yes. I noticed that as well. No idea where we waste all that time. I've put
that on the todo list of our ongoing hotplug refactoring work.

Thanks,

	tglx