linux-kernel - Re: [PATCH] hrtimer: increase clock min delta threshold while interrupt hanging

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Date:	Sat, 27 Dec 2008 11:53:34 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hrtimer: increase clock min delta threshold while
	interrupt hanging


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> Impact: avoid hanging on slow systems
> 
> While using the function graph tracer on a virtualized system, the 
> hrtimer_interrupt can hang the system on an infinite loop. This can be 
> caused on several situation where something intrusive is slowing the 
> system (ie: tracing) and the next clock events to program are always 
> before the current time. This patch implements a reasonable compromise. 
> If such a situation is detected, we share the CPUs time in 1/4 to 
> process the hrtimer interrupts. This is enough to let the system running 
> without serious starvation.
> 
> It has been successfully tested under VirtualBox with 1000 HZ and 100 HZ 
> with function graph tracer launched. On both cases, the clock events 
> were increased until about 25 ms periodic ticks, which means 40 HZ.
> 
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> ---
>  kernel/hrtimer.c |   30 +++++++++++++++++++++++++++++-
>  1 files changed, 29 insertions(+), 1 deletions(-)

applied to tip/timers/hrtimers, thanks Frederic!

Thomas, any objections/observations?

	Ingo
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