Author: Christophe Theron
Date: 21:03:19 06/19/02
Go up one level in this thread
On June 19, 2002 at 22:28:28, Tom Kerrigan wrote:
>On June 19, 2002 at 18:10:11, Christophe Theron wrote:
>
>>On the other hand, there are some processors that really require specific
>>software to get the best performances. The Crusoe processors come to mind. Both
>
>The XScale has the same ISA as the SA, so the issues can't be nearly as
>complicated as getting a Crusoe to run x86 code.
>
>>So maybe the XScale PXA250 really needs something like that. As far as I know,
>>the speed of this processor is constantly adjusted (hence the name "XScale"
>>IIRC). So it's not always running at 400MHz (for the nominal 400MHz version). It
>>is very well possible that this speed adjustement REQUIRES the OS to provide
>>some important information, like the CPU load or whatever.
>
>Sure. But how hard would it be to tell the chip to run at 400MHz on startup (if
>it doesn't by default)? Probably a few instructions. I'd hardly call this
>"optimizing" the OS.
>
>-Tom
Yes, that's not an optimization, especially if your batteries do not last more
than half an hour with this trick.
I think the OS really needs to do a good part of the job here, and to do it in a
sensible way, or you won't get acceptable results.
From what I understand from the articles I have read, using the extra computing
power available in the chip is not that obvious. Or else they would not point
this problem out.
I also admit that I do not exactly understand where the problem is. I guess it's
not only the OS which will have to take care of the details, but also the
applications themselves (which is going to make the whole story quite tricky). I
hope somebody with more knowledge about the XScale will tell us more.
Christophe
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