[squeak-dev] Re: Closure VM on XO

Levente Uzonyi leves at elte.hu
Sun Mar 6 21:53:23 UTC 2011

On Sat, 5 Mar 2011, Levente Uzonyi wrote:

> On Fri, 4 Mar 2011, Eliot Miranda wrote:
> snip
>> Does the XO Geode support sse2?  Actually, what is the exact processor in
>> the X0?  Right now the JIT won't use sse2 instructions if they aren;t
>> available, which translates into no machine code floatng-point primitives.
>> But I'm also using sse2 instructions to update the 64-bit microsecond
>> clock, so without some rewrite teh current linux Cog does depend on sse2.
> Older XO's have Geode GX, newer have Geode LX CPUs. None of these support SSE 
> at all, just MMX and an extended version of 3DNow!. There's no MFENCE (just 
> SFENCE), so an alternative implementation is necessary for these CPUs.

According to http://www.linuxjournal.com/node/8212/print mfence is only 
necessary on x86_64 platforms, so I added the following two lines before 
the else branch in sqMemoryFence.h

# elif !defined(__X86_64__)
#       define sqLowLevelMFence() asm volatile ("lock; addl $0,0(%%esp)":::"memory")

I compiled it with r2361 and it works fine on my 32-bit Ubuntu 10.04. So 
if the -msse compiler flag is removed from the Makefiles, then Cog should 
run on the XO-1 too.

The article also mentions smp_mb() which should be used on linux, but I 
couldn't find which header file defines it.


> Levente
>> best
>> Eliot
> snip

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