linux-kernel - Re: [PATCH] Improve clocksource unstable warning

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Message-ID: <AANLkTim27c_pHpawoGw3VyV9qQAF_8twJPTr5kqt6jhW@mail.gmail.com>
Date:	Tue, 16 Nov 2010 19:05:15 -0500
From:	Andrew Lutomirski <luto@....edu>
To:	john stultz <johnstul@...ibm.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	pc@...ibm.com
Subject: Re: [PATCH] Improve clocksource unstable warning

On Fri, Nov 12, 2010 at 7:58 PM, john stultz <johnstul@...ibm.com> wrote:
> On Sat, 2010-11-13 at 00:22 +0000, john stultz wrote:
>> On Fri, 2010-11-12 at 18:51 -0500, Andrew Lutomirski wrote:
>> > Also wrong if cs_elapsed is just slightly less than wd_wrapping_time
>> > but the wd clocksource runs enough faster that it wrapped.
>>
>> Ok. Good point, that's a problem. Hrmmmm. Too much math for Friday. :)
>
> I have a hard time leaving things alone. :)
>
> So this still has the issue of the u64%u64 won't work on 32bit systems,
> but I think once I rework the modulo bit the following should be what
> you were describing.
>
> It is ugly, so let me know if you have a cleaner way.
>

I'm playing with this stuff now, and it looks like my (invariant,
constant, single-package i7) TSC has a max_idle_ns of just over 3
seconds.  I'm confused.

--Andy
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