linux-kernel - Re: [VIA Support] Instruction timing and cache coherency issues

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Message-ID: <20090730090804.GE1364@ucw.cz>
Date:	Thu, 30 Jul 2009 11:08:04 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Michael S. Zick" <lkml@...ethan.org>
Cc:	linux-kernel@...r.kernel.org,
	Harald Welte <HaraldWelte@...tech.com>
Subject: Re: [VIA Support]  Instruction timing and cache coherency issues

Hi!

> Started back in mid-May - long time and a lot of hours later...
> 
> As suggested very early in this examination by others -
> It is a timing issue.  My inserting "lock" for config_mviac7
> was just poking at the edges of the sore spot.  ;)
> 
> The "break through" came yesterday while running (or trying to run)
> FreeBSD-8.0-beta2 on the various machines at hand. . .
> 
> Depending on the cpu model variation and the integrated chipset
> used with that cpu - -
> *) FB-8.0 will run
> *) FB-8.0 will only run in "safe mode"
> *) FB-8.0 panics
> 
> And that pattern is similar to the 2.6.30 cpu model / chipset pattern.
> Scratches head, asking: "now how can that be" with two very different OS designs.
> 
> Diddling with the things I have found that either "fix" or "work around"
> the various timing / cache coherency issues - - -
> Aw, so - found how to affect the timing issues sufficiently so that Linux
> would panic dump rather than deadlock on the troublesum combination - -
> *Functionally the same* panic backtrace that FreeBSD is showing.
> 
> NOW I have a lead into making a "minimum invasive" change so that the 
> kernel is happy - even on the flaky VIA combinations.  Patch RSN, just any month.
> The FreeBSD project can fix their problems themselves.  ;)
> 
> @H.W.  Download the FreeBSD-8.0-beta2 and try running it on your Cloudbook and HP-2133,
> you can see what is happening.  Then you might have a word or two with the silicon growers.
> 

So... you believe you have pinpointed bug in their cpu design?
									Pavel
-- 
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(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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