linux-kernel - Re: Improved TSC calculation

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Date:	Wed, 20 Apr 2011 16:10:18 +0100
From:	Ed W <lists@...dgooses.com>
To:	john stultz <johnstul@...ibm.com>
CC:	linux-kernel@...r.kernel.org
Subject: Re: Improved TSC calculation

On 14/04/2011 19:20, john stultz wrote:
> On Thu, 2011-04-14 at 12:19 +0100, Ed W wrote:

>> Before I try and hack probably an (inadequate) solution myself, do you
>> have any thoughts on the best solution to extend your commit to non
>> PM/HEPT machine?  My initial thought was to repeatedly call
>> pit_calibrate_tsc() with an extended latch, looking for a stable
>> solution (ie refactor native_calibrate_tsc() ).  Is this workable?
>> Better ideas?
> 
> Oof. So with the PIT you can maybe utilize the second channel/counter,
> using a largish long countdown to try to get a similar functionality.
> The only big concern is that the timer interrupt hardware is always
> problematic (every time we chanage our usage, some random chunk of
> laptops seem to stop working). So whatever solution that works for you
> might not be able to be generically deployed. But I think it could be
> interesting and might be worth you giving it a shot.
> 
> I'd probably look at reworking tsc_refine_calibration_work, extending
> the tsc_read_refs() code to also get PIT count values and then start the
> long PIT countdown on the second channel before we
> schedule_delayed_work.

OK, I have digested that and come to the conclusion that this might be a
little beyond what I can easily code up...  Any chance of some hints to
get started from those that know what they are doing here?

Cheers

Ed W
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