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Re: [PATCH]: R10000 Needs LL/SC Workaround in Glibc

To: libc-ports@sources.redhat.com
Subject: Re: [PATCH]: R10000 Needs LL/SC Workaround in Glibc
From: Kumba <kumba@gentoo.org>
Date: Tue, 04 Nov 2008 02:16:03 -0500
Cc: Ralf Baechle <ralf@linux-mips.org>, Daniel Jacobowitz <drow@false.org>, Linux MIPS List <linux-mips@linux-mips.org>
In-reply-to: <20081101112643.GA2249@linux-mips.org>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <490A912A.8030901@gentoo.org> <20081101112643.GA2249@linux-mips.org>
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Ralf Baechle wrote:

In the kernel we have very good knowledge about what types of processors
are being used for what configuration; much less in userland and the code
as suggested by you would result in a silent failure on affected R10000
machines if version built not for the R10000 was being used - iow no
improvment over what we have right now.  So for userland I'd prefer to

 o MIPS I builds: use the some 28 nops.
 o Builds for MIPS II or better: always use the branch likely
 o A runtime test would have to be implemented pessimisticall because it
   would have to rely on /proc being mounted which isn't available early in
   the boot process.  It's probably going to add more overhead than it
   saves anyway.

There is a price for using branch likely - but not that high.  In the grand
picture it'll almost certainly vanish in the benchmarking noise.

Good idea.  I'll tinker with this once I wrap my head around the gcc-side of 
things.

--
Joshua Kinard
Gentoo/MIPS
kumba@gentoo.org

"The past tempts us, the present confuses us, the future frightens us. And our lives slip away, moment by moment, lost in that vast, terrible in-between."

--Emperor Turhan, Centauri Republic

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