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Re: LL/SC benchmarking [was: Mipsel libc with LL/SC online anywhere?]

To: Richard Hodges <rh@matriplex.com>
Subject: Re: LL/SC benchmarking [was: Mipsel libc with LL/SC online anywhere?]
From: Johannes Stezenbach <js@convergence.de>
Date: Mon, 22 Jul 2002 12:35:35 +0200
Cc: "Kevin D. Kissell" <kevink@mips.com>, linux-mips@oss.sgi.com
In-reply-to: <Pine.BSF.4.10.10207190846180.1937-100000@mail.matriplex.com>
Mail-followup-to: Johannes Stezenbach <js@convergence.de>, Richard Hodges <rh@matriplex.com>, "Kevin D. Kissell" <kevink@mips.com>, linux-mips@oss.sgi.com
References: <20020719123828.GA5521@convergence.de> <Pine.BSF.4.10.10207190846180.1937-100000@mail.matriplex.com>
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On Fri, Jul 19, 2002 at 08:54:46AM -0700, Richard Hodges wrote:
> On Fri, 19 Jul 2002, Johannes Stezenbach wrote:
> 
> > I think the beql-hack needs a kernel patch to guarantee k1 !=
> > MAGIC_COOKIE after each eret, but for a those few tests I was just
> > taking my chance.
> 
> Maybe something like this in front of every "eret" instruction?
> 
> #ifdef CONFIG_CPU_VR41XX
>       move    $27,$0
> #endif

The Sony patch for CPUs without LL/SC and without branch-likely
(posted here on Tue 22 Jan 2002 15:27:44 +0900 by
Machida Hiroyuki <machida@sm.sony.co.jp>) requires to load
a certain magic cookie into k1 before every eret/rfe.

OTOH, Kevin D. Kissel speculates that for the branch-likely
trick it might be possible to find a magic value that already can
never end up in k1 after an eret, as side effect of the
current implementation. So we wouldn't have to patch the
kernel at all.

I for one would be content if I could find a magic cookie value
that lets me avoid adding instructions to the TLB refill handler.


Johannes


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