Message-ID: <3EF26C85.5090507@vgertech.com>
Date: Fri, 20 Jun 2003 03:08:05 +0100
From: Nuno Silva <nuno.silva@vgertech.com>
Organization: VGER, LDA
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To: Linus Torvalds <torvalds@transmeta.com>
CC: Samphan Raruenrom <samphan@thai.com>, Vojtech Pavlik <vojtech@suse.cz>,
       linux-kernel@vger.kernel.org
Subject: Re: Crusoe's persistent translation on linux?
References: <Pine.LNX.4.44.0306191707000.1987-100000@home.transmeta.com>
In-Reply-To: <Pine.LNX.4.44.0306191707000.1987-100000@home.transmeta.com>
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Hi!

Linus Torvalds wrote:
> On Fri, 20 Jun 2003, Nuno Silva wrote:
> 
>>This raises a new question. How about a port of Linux to the "VLIW" so 
>>that we can skip x86 "code morphing" interelly?
> 
> 
> The native crusoe code - even if it was documented and available - is not 
> very conductive to general-purpose OS stuff. It has no notion of memory 
> protection, and there's no MMU for code accesses, so things like kernel 
> modules simply wouldn't work.
> 
> 
>>I'm sure that 1GHz would benefit from it. Is it possible, Linus?
> 
> 
> The translations are usually _better_ than statically compiled native 
> code (because the whole CPU is designed for speculation, and the static 
> compilers don't know how to do that), and thus going to native mode is not 
> necessarily a performance improvement.
> 
> So no, it wouldn't really benefit from it, not to mention that it's not
> even an option since Transmeta has never released enough details to do it
> anyway. Largely for simple security concerns - if you start giving
> interfaces for mucking around with the "microcode", you could do some
> really nasty things. 


Authoritative answer received! :)

Thanks,
Nuno Silva


> 
> Process startup is slightly slower due to the translation overhead, but
> that doesn't matter for the kernel anyway (so a native kernel wouldn't
> much help). And we do cache translations in memory, even across
> invocations. I suspect the reason large builds are slower are due to slow
> memory and/or occasionally overflowing the translation cache.
> 
> 			Linus
> 
> 


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