K8L and Penryn

It just amazes me to see how AMD fans keep on saying, "K8L will make Conroe look obsolete," or "Intel needs someting a lot better than Conroe if it has to survive K8L onslaught." That's funny, considering these same fanboys were saying that with Conroe, Intel will not be able to close gap on K8. That is funny...

Let us just look at some of the facts. In video encoding, at the same clock speed, Conroe beats K8 by about 30%. In games, if the GPU bottlenect is removed, Conroe beats K8 by upto 50%. So, it is safe to say that Conroe, in general is better than K8 by about 30%. Now, first we have to understand that K8L will go against Penryn--Conroe's 45 nm cousin. Also, sometime back, Inquirer reported that Intel's 45 nm process is a giant leap over its 65 nm process, as far as leakage is concerned. If this is indeed true, Conroe's 45 nm sibling, Penryn, would not have any trouble clocking at 4 GhZ, while operating in the same or lower power envelope. Recent reviews of Kentsfield also show that Conroe architecture is not hurting for memory bandwidth.

So what does all this mean? If Penryn clocks at 4GHz, it will be 33% faster than X6800. Now, even though Conroe performance scales almost linearly with speed, let us give it some headroom, and assume that this additional 33% clock-speed will give it only 25% performance improvement. Considering that X6800 beats AMD's best by 30%, this means, top-end Penryn will beat AMD's best (as of today) by 62%. Now that is huge!! Now beating that is not going to be an easy task, for K8 or K8L.

AMD fanboys might say--K8L is a grounds up architecture built of performance, and it should not be too difficult for it to improve over K8 by 62%. Well, let us take a look at what K8L brings to the table.

First, improved SSE performance. Yawn!! It was time. Conroe beats AMD in pure SSE2 operations by 400%. Nothing that AMD does here is going to tilt the balance in the other direction.

Second, it adds load reordering. Another bit of a Yawn! Intel has been doing that for how many years now? Conroe also does load/store reordering. Nothing new here.

Third, it adds support for HT 3.0. Last I checked, K8 was not really hurting for memory bandwidth. So this is not expected add too much to real performance. Extremely good for bragging rights, but from end-user's perspective, another yawn.

Fourth, it adds dual-ported L1 cache. AMD might be onto something with this. But again, we do not know what it really means. In fact, personally I do not expect it to add a lot. How many workloads today are really hurting for cache bandwidth. I would say, not many. Definitely not the 32-bit ones. At an IPC of about 2, and at most two source operands per instruction, you do not need more than 16 byte reads per clock cycle. For 64-bit workloads, it *MAY* mean someting. But again, until we see the effect on real benchmarks, I wouldn't start jumping up and down. Add to that the fact that K8L won't be reordering loads and stores. That means, if there are stores in front of loads, the second cache port could be just sitting there, doing nothing. Actually not entirely true, the second cache port will be adding load to the cache, increasing power conumption. In short, this seems like a good feature, but unless there is evidence to the contrary, I wouldn't count too much on it.

Fifth: improved floating point performance. Well, AMD has always been strong in this area, and when it comes to editing word documents, unzipping files, compressing videos, and playing games, it means zilt!! Universities and NASA care about it--impling 99% of their computers will be from AMD instead of 95%. But again, it is a performance improvement tailored for a very niche market.

Finally, they add shared L3 cache. Time they did so, wouldn't you say? Whatever happened to all those claims about cache thrashing, makes you wonder...

You might say, this is a very one-sided view. If Intel managed such a huge performance improvement from P4 to Core 2, why can't AMD do the same from K8 to K8L?

For first, Intel did not improve performance going from P4 to Core 2, they improved power. You can take P4, cool it with liquid nitrogen, clock it at 6 GHz, and it will beat the crap out of any CPU on the planet. The problem is, no one wants to do that, and hence Intel has to clock it below 4 GHz. Unfortuantely, P4 was designed to be performant at 5+ GHz. Realizing this mistake, what Intel did with Core 2 is that they came up with an architecture that works great at sub-5GHz range. No matter what you do to Core 2, you cannot clock it beyond 5GHz. If you take 5 GHz Conroe and 7GHz P4, they will probably be pretty close in performance. However, since no average user clocks in that range, P4 seems far inferior to Core 2.

In short, Intel saw the huge performance improvement going from P4 to Core 2 because they changed the philosophy. I wouldn't expect the same type of performance jump when Intel goes to Nehalem, for example. And that is why, I do not expect such a huge performance jump going from K8 to K8L--afterall, there is no huge change in philosophy. K8L will definitely be better. Will there be a wow factor? Hard to tell at this point. However, considering that Intel's transition to Core 2 has already set expectations very high, I think K8L will hugely be a disappointment.