AMD Athlon 64 Performance Preview

k-hell writes "It seems like X-bit Labs have gotten their hands on an 'engineering sample of the AMD Athlon 64 2800+ processor'. Damage at Tech Report is writing that 'This is really fun, but I am a little concerned about their memory latency numbers.'"

Comments

3DNow!: Cause of Slow Clock Frequency in InnerCore

[Anonymous Coward]

The review of the Athlon 64 notes that the core frequency is actually less than that in the Athlon XP. The reason is that the wires are being loaded down with too many transistors, so the resistance-capacitance (RC) time constant is too high. I doubt that the AMD engineers are somehow less capable than the Intel engineers in designing transistor interconnects with low RC time constants.

So, what could be the problem? The problem is that AMD is trying to support too many instruction sets. AMD should have axed 3DNow! and swallowed its pride. Supporting MMX, SSE, and SSE2 is sufficient.

When you try to put everything and the chicken sink into a chip, you inevitably pay for it with a slower clock speed.

My Observations

[MBCook]

Well, first off I'll say that I agree that we need units on the memory latency. If they are in a unit of time (microseconds or something) then they really show what can be done with an onboard memory controller. But onto more "important" things.

The processor doesn't take to many benchmarks, but you can't fault it too much. It's nice to see some numbers are the CPU in 32 bit mode, but let's not forget that EVERYTHING here is 32 bit (OS, programs, etc). I'd LOVE to see a comparison between 32 bit programs running under and identicle OS versions that do and don't support 64 bits (Win XP vs Win XP for x86-64 for example). I'd suspect that the performance would go up with a 64 bit OS (especially on the games, where drivers and such play such a big part). Considering it's clockspeed, it holds up very well. The fact that it's almost never far behind a current athlon with an identicle performance rating (which is actually like 400 mhz faster) shows that it can definatly run things well. This isn't the horridly crippled performance that we've all heard about with the Itanic.

So what's my take on all of this? I think that this shows that the x86-64 can really become a success. I know some of you out there are thinking "Why would I buy one? I've got a 2.4 ghz Octium 7 and my PC is faster than that thing." That may be true, but many people aren't like you. My fastest computer is a PIII 933, so even at 1.6 ghz that Athlon64 can run circles around my best PC. If you are using a PC that's even a year or so old, you can probably benefit alot if you were to move up to an Athlon64 when it comes out.

My notes on some specific benchmarks:

• 3DMark 2k3 - The chip is only 4% behind the P4 despite the fact it's clocked at only about 60% of the P4. Impressive.
• 3DMark 2k1 - The A64 is nearly identicle to the P4, despite the massive clock difference. And this is 32 bit code. Compiling a game for the x86-64 is supposed to increase performance up to 30%. Drooling yet?
• UT2003 - The A64 is nearly 10% FASTER than the P4, despite the clock difference. "Office" benchmarks may not look impressive, but games are what counts ;)

Now my objections to the benchmarking

• Where is the 1.6 ghz P4 in this? They could underclock the P4, or just get a TRUE 1.6 ghz P4 so we can see how they compare clock for clock.
• No 64 bit OS. I'd have liked to see them run Linux so they could do some tests to see how it performed with 32 bit code (UT2k3, Q3, etc) under a 64 bit OS. I understand that Windows isn't out yet so they couldn't use it.

My final thoughts are this: it looks quite promising, and I can't wait to see more. More and more people with comeout with benchmarks as time goes on, and with the Opteron released now, we'll soon see benchmarks of it in SMP mode against other chips in both 32 and 64 bit OSes with 32 and 64 bit code. Either way, it looks like it's more successful than the Itanic.

tested with windows

[paradesign]

in 32 bit mode... wtf?

couldnt they have used any one of the 64bit linuxes? this sounds like a bs review to me;

very old rev

[Anonymous Coward]

Being that I am an AMD employee, I know for a fact that B0 (the version of clawhammer that they are benchmarking) is a very early rev, and should not even be considered when thinking about final benchmarks. Geez.

Well, one thing is for sure, xbit labs just blew their chances of ever getting their hands on another upcoming bleeding edge technology again.

Re:Check out date on processor.

[certron]

While this is 110% pure speculation, there are other numbers on the CPU. The one that I'm looking at is 0301 (2nd line of numbers/letters) which I will guess to be 1st week 2003. However, since this is pure speculation, and they got their hands on it *somehow* it could just as easily be 3rd week 2001.

OK, so that doesn't clear up anything. :-)

UT2003...

[Nameles]

Wasn't that designed with 64-bit processors in mind?

Now this doesn't make much sense, because how can you run that in 64-bit mode even though you have a 64-bit processor, when the OS is running in 32-bit mode?

Or am I dreaming?

Re: athlon 64 performance.

[Hoser McMoose]

The other enhancements to the chip more than make up for it. In fact, it should typically perform anywhere from 5-25% faster than an equally clocked AthlonXP.

The big downside to a longer pipeline is that it increase the performance penalty of flushing the pipeline after a mispredicted branch. However, AMD did two things here. First the Athlon64 has a better branch predictor than the AthlonXP, which should reduce the number of mispredicted branches. The second thing that AMD did was to change the pipeline slightly so that the extra pipeline stages don't need to be flushed on a missed branch.

FWIW AMD is kind of following Intel's lead in this regard. While the P4 has a VERY long pipeline (twice the length of the Athlons), it doesn't take all that much of a performance hit for a missed branch because they don't need to flush all of their pipeline. The P4 also has excellent branch predictors (second only to the old AMD K6 in the x86 world from what I've seen). That being said, the P4 still has a very long pipeline and very small L1 caches, as well as a number of odd quirks as to what instructions can be where in the pipeline, so the end result tends to be a reduction in the average IPC of the chip vs. the AthlonXP/64.

As for clock speeds, my understanding is that AMD is aiming for the 2.0GHz range when they bring the chip to market.