linux-kernel - Re: intel_pstate_timer_func divide by zero oops

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Message-ID: <5153B03E.2050201@gmail.com>
Date:	Wed, 27 Mar 2013 19:51:42 -0700
From:	Dirk Brandewie <dirk.brandewie@...il.com>
To:	Parag Warudkar <parag.lkml@...il.com>
CC:	rjw@...k.pl, cpufreq@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	dirk.brandewie@...il.com
Subject: Re: intel_pstate_timer_func divide by zero oops


Is there any way to capture the beginning of this trace?

pid_param_set() is on the stack which means that something is changing
the debugfs parameters or the stack is FUBAR.

On 03/27/2013 06:49 PM, Parag Warudkar wrote:
> I get this same oops occassionally - the machine freezes and there doesn't
> seem to be any record of the oops on disk.
>

>
> That  is -
> 	sample->pstate_pct_busy = 100 - div64_u64(
> 					sample->idletime_us * 100,
> 					sample->duration_us);
>

I don't see how duration_us can be zero unless somehow I am getting back-to-back
timer callbacks which seems unlikely since the timer is not re-armed until
the timer function is about to return and the driver has done all its work
for the sample period

--Dirk

> So looks like sample->duration_us is 0? If so, that implies that
> ktime_us_delta(now, cpu->prev_sample) is zero. I am not entirely sure how
> to handle this case - return if sampling too early, or if there is some
> other bug making the delta calculation go poof.
>
>
> Thanks,
>
> Parag
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