P4 IPC also goes down as speed goes up?!

eden

Champion
Ok I hope this won't look like a troll post from Meltdown (he did something similar in the past), but did anybody notice how big 266MHZ gap jumps per speed grade of the 3 new CPUs, had rather meager performance boosts compared to the 2.53GHZ towards 2.8GHZ or even the 2.66 on 2.8, a 133MHZ jump?
Some tests showed the 266MHZ jump added the same amount of points or FPS or reduced time!

Now first I am aware of the recent controversy of the veracity of this article's test and its results, and also that normally you cannot have the same IPC gained linearly as CPU speed scales, not to mention after seeing the clock performance problems the AXPs are getting at high speeds which could hint at this case, but 533MHZ FSB SHOULD be plenty, and not to mention sometimes it lagged behind in non-bandwidth intensive apps as well.
It may be a normal thing, but still, 266MHZ more should not become less beneficial just like that. Anyways, it probably is not true or won't be the same, however anyone who has any conclusions, explanations, provide!

On a side-note, anybody notice Banias may use PR ratings? I wouldn't be surprised since it is some hybrid P6-P7 core. I feel excited about it, when hearing about some different core architecture in some way! But also, I thought Intel might be honest about showing the speed simply, but I guess they are known for high numbers, so it makes sense they want to keep it "big". Anyway it is sketchy info and more should come later at IDF, which is pretty exciting already!

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When buying an AthlonXP, please make sure the bus is at 133MHZ, or you will get a lower speed!<P ID="edit"><FONT SIZE=-1><EM>Edited by Eden on 09/10/02 10:00 PM.</EM></FONT></P>
 

taylanator

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Jan 18, 2002
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whatever happened to meltdown anyway? That guy was crazy. I agree with you in the since that there should have been a higher performance gain and that 533mhz is plenty but I don't have any conclusions myself on this matter.
 

dhlucke

Polypheme
AMDmeltdown was institionalized. Hopefully he'll be released shortly.

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imgod2u

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In an architecture like the P4, 133MHz QDR is not really "enough" at the higher speeds of 2.8ish GHz. At 2.2, an increase from 100MHz to 133 brought about a significant performance increase. That indicates that even at 2.2 GHz, it was bandwidth starved with 100MHz QDR.
Also keep in mind it's not the bandwidth that's critical when you're CPU scales faster than your memory, it's the latency. unless you're making multiple accesses to your memory at once, an access command from the CPU could take 7 cycles (FSB cycles, not chip cycles) to reach the memory and then take even longer to access said column and row in memory. As CPU cycles increase to 200x the frequency of the FSB, more and more CPU cycles wait idly while the access signal is being transfered through the FSB.
Now, prefetch does help this a lot, but it isn't perfect and it doesn't work all the time. So you will still have cache misses and no matter what tricks you use to speed up bandwidth, latency will still be bad.
Also, keep in mind that while the 2.8 GHz part is increasing, the CPU is not all that matters. In games, the video card takes up a large portion of the game processing and unless you're running in a situation that is completely bottlenecked by the CPU (which doesn't happen very often) the CPU will not scale linearly as far as performance in games.

"We are Microsoft, resistance is futile." - Bill Gates, 2015.
 
make sure you arn't compareing a 2.4ghz with the 400mhz bus and a 2.4ghz at a 533mhz bus speed. Also i think the benchmark mixed DDR and RDRAM in that batch.


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eden

Champion
No no, if matching RDRAM PC1066 for the over- 3GHZ CPUs, yeilded weaker than 266MHZ jumps like the 2.53 to 2.8GHZ, even if they used DDR, then something is wrong.
Perhaps imgod2u is right.

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