Conclusion
Our testing reveals that many workloads are still very much incapable of taking advantage of more than two cores. Titles like WinZip have not yet been optimized to run more than one thread, and it's a shame. Even the cheapest dual-core processors could deliver much better performance, if only the software would support it. This not only applies to the Lame MP3 encoder, but also to Apple’s iTunes and Adobe’s Acrobat 9, which is used for creating PDF documents. Since Apple and Adobe aren’t exactly nobodies, this fact disappoints even more.
But let’s get back to our scaling analysis. Switching off processing cores will not reduce system idle power. AMD did a great job of mastering its power management on the 45 nm Thuban core. The system runs within the same 81W to 83W whether one or six cores are used. However, the results in peak power consumption show that average power draw per core drops with additional cores. In the end, peak power doesn’t differ much whether four, five, or six cores are active. Yet, performance still increases considerably under thread-optimized workloads.
For this reason, AMD’s Phenom II X6 offers great performance, thanks to six processing cores, as well as increased efficiency as you scale up core count. Clearly, utilizing as many cores as possible maximizes performance per watt power efficiency. In other words, given that idle power doesn’t change, and both performance and power efficiency increase with the core count, it doesn't make sense to switch off cores manually.
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An ok article, but I would have been interested to see maximum overclock at each point, even if it was without a full set of benchmarks.
Now if only AMD can upgrade its L3 cache technology...
Why is the system idle power so much higher than the system peak power (until you get to 6 cores when it's a match)?
Why is the system idle power so much higher than the system peak power (until you get to 6 cores when it's a match)?
Ah, because they should be %age graphs but the legend is in Watts. Doh!
Is the diminishing performance improvement as cores are added perhaps due to the L3 cache memory bottleneck? This diminishing return on extra cores has been highlighted in many previous articles, I was just wondering how much of the story is explained by the memory bottleneck as opposed to other I/O resource bottlenecks.
Good to see that our article on Multi-Core efficiency on the 1090T here:
http://www.hardwarereview.net/Revi [...] -1090T.htm
has spurred others onto focusing on this crucial area given that raw clock speeds have hit a ceiling some time ago.
Keep up the good work (AT has the resources to run far more tests more thoroughly than we could)
It really shows that unless you are doing media encoding/transcoding, you will have little use for more than 2 cores.
But even with that application, adding cores beyond 3 or 4 starts to equal diminished returns. Clearly it is because it is hitting the memory bandwidth wall. Guess we need DDR5 RAM.
A triple/quad channel controller plus larger L3 cache should help a bit.
Nothing that we all here didn't already know about.
Is the diminishing performance improvement as cores are added perhaps due to the L3 cache memory bottleneck? This diminishing return on extra cores has been highlighted in many previous articles, I was just wondering how much of the story is explained by the memory bottleneck as opposed to other I/O resource bottlenecks.
In the Phenom II it clearly is a bottleneck (although a relatively minor one). But the Intel i7-980X saw its L3 cache increased by a third, just like its core count, and there still was a diminishing return. A smaller one, but still.
However, as for the Phenom II it's impossible. They could never have stayed within the 95W/125W power limit with additional cache (unless AMD would have opted for a die shrink, massively increasing development time). And that would have posed a problem as not all AM3 boards support 140W and none can go higher. A bad signal for a company that has backwards compatibility as one of its prime selling points...