linux-kernel - Re: [PATCH v2] tracing/function-graph-tracer: prevent from hrtimer interrupt infinite loop

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Date:	Thu, 18 Dec 2008 22:36:19 +0100
From:	"Frédéric Weisbecker" <fweisbec@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Thomas Gleixner" <tglx@...utronix.de>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] tracing/function-graph-tracer: prevent from hrtimer interrupt infinite loop

2008/12/18 Ingo Molnar <mingo@...e.hu>:
>
> * Frédéric Weisbecker <fweisbec@...il.com> wrote:
>
>> Hmm. No, I just tested by setting 1000 HZ and disabled NOHZ, the system
>> doesn't lockup unless I turn on the function graph tracer.
>
> but that's what we are interested in: the system locks up with HZ=1000 and
> with the tracer on - right?

Yes.

> Which means that it's not some hrtimer problem, but simply the traced
> timer tick takes more than 1 millisecond to execute under this
> virtualization.
>
>        Ingo
>

Oh ok I see. Sorry I'm a bit slow today...
So the solution would be to adapt dynamically the timeout between
hrtimer irq. But I don't know that much hrtimer
to implement such a feature...
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