Re: Questions about notebooks and Debian
On Fri, Aug 03, 2001 at 01:08:00AM -0300, Peter Cordes wrote:
> On Thu, Aug 02, 2001 at 07:05:44AM +0200, Sven wrote:
> > Err, isn't that 256Ko of on die cache, like the PIII and the later athlons ?
>
> The PPC 750 does not have on die L2 cache, but gets almost as good
> hit latency by putting the cache-management logic (tag lookup, etc.)
> on die, and having a dedicated L2 connection bus.
no, the G3 in the new ibook is a IBM ppc 750Cx or Cxe, with 256Ko of backside cache,
as can be seen in the tech sheet :
-----
500-MHz PowerPC G3 processor with 256K on-chip level 2 cache.
-----
Also notice, that the ibook is one of the lone notebook that has a ATI Rage mobility 128
as it's graphic chip, most others have plain rage boards, or other kind of graphics.
The only one competitive in this area are priced twice as high, and have either rage 128
or nvidio go chips. But still there are not many.
> IIRC, apple chose to run the L2 at half the proc clock speed. (The
> chip allows the board designer to set the clock ratio to use for the
> L2 bus, from 1:1 on down.)
This is true for older ibook or powerbooks, but no more for etiher the new ibook nor
the new imacs.
> > > iMac G3 400 (which has 512k of this same cache).
> >
> > Did you do any benchmarking on it ?
> >
> > > If you want a powerhorse of a laptop, get a TiBook, or an x86 laptop.
> > > The x86 will give you a crappy architecture, and not much battery life.
> >
> > but the TiBook costs twice as much and more, and as said battery life on i386
> > is very bad, especially on the athlon/duron based ones.
>
> Battery tech is getting pretty good. My friend got a 1GHz PIII
> laptop with 512MB RAM, and he says the battery lasts 3-4 hours IIRC.
> I asked him how toasty it got, and he said it wasn't very nice holding
> it in his lap...
Sure, but was the processor actively working ? and what kind of battery does it have. I guess
it was magnitudes higher that the one in the ibook, which only has a 42 Watt/hour battery
(which makes it use ~ 8Watts/hour, there is noway you can achieve that on a i386 box.)
Anyway, you can't forget that the G3 eats less that 5W of power, while the 1Gz PIII
want around 15-20Watts, i think, that is when it is not being downstepped to run ~300MHz
or such. And the duron case is worse, since it wants around 25-30Watts.
> One important thing to note is that GCC's codegen for PPC takes
> longer than for x86. This means that compiling the kernel is not a
> relevant benchmark for comparing compute power of x86 vs. PPC. It is,
> however, an appropriate benchmark for seeing how long it takes to
> compile stuff. If compiling stuff is one of the things that you do
> that actually matters how long it takes, then it's something to think
> about. (some stuff takes so little time that it doesn't matter which
> machine does it faster, like running ls. ls runs fast enough on any
> new machine. 0.1ms vs. 0.2ms doesn't matter. Compiling a kernel (or
> the project you're working on) is something that takes long enough
> that you have to do something else while it happens, so it does matter
> how long it takes.)
YEs, i guess the appropriate benchmark would be to have a cross compiler on
both boxes, building for a common arch, with a common config file.
But still then there would be some difference.
Also, the main app is not gcc, not for everyone that is.
Also some apps (like openGL and such) are 3dnow/mmx/katmai optimized, but
not yet altivec optimized (will this ever come), which anyway is irrelevant on
a G3.
also RISC code is bigger than CISC one, so it would also take longer to load it from the disk.
Friendly,
Sven Luther
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