Re: Crusoe's persistent translation on linux?

Nuno Silva
2003-06-20T01:53:51Z

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
>
>