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

To: Johannes Stezenbach <js@convergence.de>
Subject: Re: LL/SC benchmarking [was: Mipsel libc with LL/SC online anywhere?]
From: Richard Hodges <rh@matriplex.com>
Date: Fri, 19 Jul 2002 08:54:46 -0700 (PDT)
Cc: "Kevin D. Kissell" <kevink@mips.com>, linux-mips@oss.sgi.com
In-reply-to: <20020719123828.GA5521@convergence.de>
Sender: owner-linux-mips@oss.sgi.com
On Fri, 19 Jul 2002, Johannes Stezenbach wrote:

> I'm working on a platform without LL/SC, an embedded system/SOC
> with a NEC VR4120A CPU core. To find out the effect of sysmips
> vs. emulated LL/SC vs. the branch-likely trick posted by
> Kevin D. Kissell <kevink@mips.com> on Tue, 22 Jan 2002 18:16:25 +0100
> I created an experimental patch for glibc-2.2.5 which allows
> run-time switching of the _test_and_set() and __compare_and_swap()
> implementation based on the presence of two "switch files" in /etc/.

...

> 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

I am also working with an NEC core, and would much prefer to perform
atomic operations in user space.  (I understand that this trick is
probably not SMP safe - I don't really care.)

-Richard


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