On 10 Sep 2001, at 0:44, Stephan T. Lavavej wrote:
> So, will the Pentium 4 Northwood core (with 512KB L2 cache as
> compared to the current Willamette's 256KB L2 cache) perform
> even better on Prime95? Will there be a setting to tell Prime95
> that a Willamette or Northwood core is specifically being used
> (as opposed to just "Pentium 4")?
Well - there was no need for any change to the code when the PIII
changed from 512KB L2 cache running at half speed (Klamath) to
256KB L2 cache running at full speed (Coppermine), or when a
similar change occurred in the Athlon line with the introduction of
Thunderbird.
Neither is there any need for the code to differentiate between
Celeron 2 and PIII chips - the essential difference here is that the
C2 has only 128KB of L2 cache - or between Thunderbird and
Duron in the Athlon line.
So I don't see any need for there to be anything to differentiate
between different cache sizes on Pentium 4.
A larger L2 cache will do no harm, though with data set sizes
much bigger than the L2 cache, it probably won't help much either.
(What's the difference in Prime95 benchmarks between a Celeron
800 and a PIII 800 (100 MHz FSB) in the same system?)
Larger caches will benefit multiprocessor systems more than
uniprocessor systems, _provided_ the work is allocated to
processors using an efficient algorithm so that cache contents are
not wasted by processing the data on another processor.
If there is a change in the instruction set that can be exploited, or a
significant change in relative timings for particular instructions
between one variant of a processor and another, then maybe it
might be worth forking the code (again), but IMHO it's better to
keep forks to the minimum for two basic reasons:
(a) reducing development & maintainance load;
(b) avoiding confusing users, as far as possible.
BTW the new "Tualatin" PIIIs built using 0.13 micron technology
have 512KB L2 cache. I'm not sure whether they can be used in
existing FP-CGA mobos - you're likely going to need at least a
BIOS upgrade; there may be other electrical considerations e.g.
provision of the lower voltage required by the Tualatin core may not
be possible without changes to the voltage regulator hardware.
For the sake of anyone wishing to upgrade I hope the compatibility
issues are resolved soon - Intel is already saying that the desktop
PIII will be withdrawn from sale in early December!
Regards
Brian Beesley
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