Re: Crusoe's persistent translation on linux?

[Nuno Silva]

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
> 
>