linux-kernel - Re: Yet more softlockups.

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Date:	Fri, 12 Jul 2013 12:07:28 -0600
From:	David Ahern <dsahern@...il.com>
To:	Dave Jones <davej@...hat.com>, Dave Hansen <dave.hansen@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Peter Anvin <hpa@...or.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: Yet more softlockups.

On 7/12/13 11:50 AM, Dave Jones wrote:

> Given you can run trinity long enough that you hit this however, makes me
> think you won't be able to triger the bug I'm talking about.
> Perhaps virtualised perf counters are somehow immune to this problem, because
> on bare-metal, it literally takes seconds.

I can generate the message it just does not lock up:

...
[  131.837129] perf samples too long (35849 > 35714), lowering 
kernel.perf_event_max_sample_rate to 4000
...
[  237.271170] INFO: NMI handler (perf_event_nmi_handler) took too long 
to run: 57900.001 msecs


And Dave Hansen: I think nmi.c has the same do_div problem as 
kernel/events/core.c that Stephane fixed. Your patch has:

         whole_msecs = do_div(delta, (1000 * 1000));
         decimal_msecs = do_div(delta, 1000) % 1000;

David
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