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Re: Deskstation info

To: linux-mips@fnet.fr
Subject: Re: Deskstation info
From: Dom Sweetman <dom@algor.co.uk>
Date: Mon, 13 May 1996 09:03:17 +0100
In-reply-to: <9605121136.AA04000@thoma..uni-koblenz>
References: <169.199605120847@gladsmuir.algor.co.uk> <9605121136.AA04000@thoma..uni-koblenz>
Reply-to: dom@algor.co.uk
> [discussing speed of RM200 vs other R4600 machines, and BogoIPS:]

>       .set    noreorder
> 1:    bnez    reg,1b
>       subu    reg,1
> 
> ... the first MIPS machine I ported Linux to - a Deskstation Tyne
> with a R4600/133MHz - needed three cycles to execute this loop while
> this machine seems to execute the loop in *one* cycle.  

Bizarre.  It should take 2 cycles/loop on *any* R4600, and 4
cycles/loop on an R4000/4400.  I'd put money on it *not* taking one
cycle/loop - only an R10000 can do that!  There are some unlikely
reasons I can think of for the difference (eg the loop spans a page
boundary and is in mapped space, when it will repeatedly have to do a
micro-tlb refill - but I'm sure you're in unmapped space).

> There are two versions of the R4600; my Tyne had version 1.0 as far as
> I remember while the SNI box has version 2.0.  The 2.0 chip has some
> bugfixes; most important is probably the way it accesses primary caches.
> This bug can be worked around by disabeling interrupts during cacheflush
> or (untested ...) flushing way B before way A of the cache.

I don't recall anything on the published Rev 1 buglist which would
affect this.  Now you've got me intrigued... I'd better go look this up!

> What type of benchmark would you account as real world benchmark?

Any modest set of reasonably large applications which can be compiled
without change on a number of different platforms, and run and timed
off test data.  Perl/groff/emacs running scripts might be good.
I hoped this might have been so straightforward
between two Linux machines that someone had just done an informal
run-off. 

> If you need "realworld" benchmarks probably some guy at MTI might supply
> you more representative data than I could.

MTI have commercial interests here, so it's not quite fair to expect
them to be objective.

> I've just booted the RM200 successfully via NFS.  Time for porting
? Linux/MIPS to RM200 so far: a bit more than two days :->

Congratulations! we'd better try and find you one of our boards...

Dominic Sweetman
dom@algor.co.uk

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