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Re: Decstation broken Was: CVS Update@oss.sgi.com: linux

To: Ralf Baechle <ralf@oss.sgi.com>
Subject: Re: Decstation broken Was: CVS Update@oss.sgi.com: linux
From: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Date: Mon, 2 Oct 2000 13:59:03 +0200 (MET DST)
Cc: Florian Lohoff <flo@rfc822.org>, linux-mips@oss.sgi.com
In-reply-to: <20000930121823.A32244@bacchus.dhis.org>
Organization: Technical University of Gdansk
Sender: owner-linux-mips@oss.sgi.com
On Sat, 30 Sep 2000, Ralf Baechle wrote:

> >  Well, I asked for testing before the commit, but nobody bothered to write
> > anything, so I assumed everything is correct, sigh...
> 
> Not sigh ...  The lesson that not speaking up is a also wrong!

 Well, if nobody reports a problem with a patch, it means it's either fine
or nobody bothered to test it.  For me both cases mean it's OK to apply
it. 

> The ddiv usage outside of do_div / do_div64_32 is actually ok because

 But can't we receive an exception for some reason???

> interrupts are always disabled.  We don't have the same guarantee for
> do_div / do_div64_32 calls.

 Yep -- it's used for printk.

> Hmm...  We got two error scenarios left - bus errors and cache errors.  If
> we get one of those doomsday is near anyway ...  Anyway, these are rare,
> so we rather make these exception handlers pay the price.

 I'd see two approaches: either wipe 64-bit code out completely (clean and
elegant -- I'd vote for it, even though there is performance penalty) or
disable interrupts around the 64-bit division (the window would be small
and it would still be a performance win, but it's ugly as hell).  What do
you think? 

  Maciej

-- 
+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+--------------------------------------------------------------+
+        e-mail: macro@ds2.pg.gda.pl, PGP key available        +


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