What to bear inmind when you’re expecting AMD Zen

What to bear inmind when you’re expecting AMD Zen


Last week, the first purported benchmarks of AMD’s upcoming “Zen” microprocessor leaked, giving us an early glimpse of how the chip performs vis-à-vis various Intel products. While the leaks haven’t been confirmed as genuine, it was interesting to see the conversation around Zen and AMD’s expected performance level. Then, at an event on Wednesday, AMD showed some demos of Zen running clock-for-clock against Intel’s 5960X. While these demos were not performed at full speed, they offered some evidence that AMD could match Intel clock-for-clock in certain workloads — and while such demos are always cherry-picked to favor one’s own company, they gave some additional context on what Zen can do.
What I want to talk about here has less to do with AMD’s demo or specifics of the architecture and more to do with what AMD needs to deliver to be considered a success. One thing I’ll say up front: I have no secret sources, no hidden informants, and no leaks to credit for what I’m about to write. Agree or disagree, these are my own thoughts and observations.
AMD-Zen-02
AMD claims that Zen will have 40% better IPC than its previous Excavator architecture and it’s shown demos illustrating how Zen can compete clock-for-clock against the 5960X in some workloads. This is both a solid indication of where the chip currently is and a generalized prediction of where it could end up. The details and specifics will depend on a number of factors including final clock speeds and application-level optimization.

What does 40% more IPC mean, anyway?

IPC stands for instructions per clock or instructions per cycle (the two terms are synonymous). It’s a metric of CPU efficiency — the higher a CPU’s IPC, the more work that CPU can perform in a given amount of time.
There’s typically an inverse relationship between a CPU’s clock speed and its IPC. While IPC has always been used to measure CPU performance, the term became common in enthusiast circles when Intel debuted the original Pentium 4. While the P4 was clocked much higher than its Pentium 3 predecessor, the amount of work it performed per clock cycle was significantly lower. The net result of this was that the Pentium 4 1.5GHz often struggled to outperform the slower Pentium 3 1GHz or its Athlon K7 counterpart from AMD.
The most common way to parse AMD’s statement is as follows: If you took an Excavator CPU and a Zen CPU and ran them at the same clock speed, the Zen CPU should be 40% faster, on average, then the AMD CPU it replaces. But even here, there have been questions: Does that 40% IPC improvement include the impact of simultaneous multi-threading (what Intel calls Hyper-Threading) or not? Is that based on two chips clocked at the same frequency or not? Finally and most importantly, which tests were used to derive that figure? IPC isn’t a constant — it fluctuates a great deal based on the behavior of the target application.
Maxwell-Performance
The benchmark above is from tests I ran when Bulldozer launched nearly five years ago. Despite losing to AMD’s older six-core X6 1100T in multiple benchmarks, the FX-8150 was actually significantly faster in Maxwell Render — one of the few tests it unilaterally won. This kind of variance is normal, which is why it’s so difficult to draw conclusions about relative chip performance based on any single metric. AMD’s claimed 40% IPC uplift should be treated like a general or average prediction and not the guaranteed result of any single test.

How will Zen compare with Intel CPUs?

The real question, of course, isn’t whether Zen will improve on Carrizo, but whether it’ll give AMD a CPU that can compete with Intel. The realistic answer is “It’ll depend on where you look and what you’re looking for.”
Here’s what I mean by that. Compare AMD’s current top-end Piledriver, the FX-9590, against Intel’s Core i7-6700K using Anandtech’s Bench tool. I’ve snipped a section of tests to include below, but you can view the full comparison here. In the graph below, blue is for the FX-9590, while the orange-ish bar is Intel’s Core i7-6700K.
Assume for a moment that these FX-9590 results actually reflected Excavator performance instead of Piledriver. Now, assume they were 40% faster than they actually are. Would this theoretical top-end chip offer competitive performance with Intel? In some tests, it absolutely would. In other tests, the gap between AMD and Intel is large enough that even a 40% improvement isn’t enough to allow AMD to catch its competitor. Those of you who want to perform this comparison using actual data from Excavator can refer to this AT review of the chip and do the math from there. Either way, the point holds — there are tests where a 40% improvement would absolutely be enough to allow AMD to catch Intel and tests where it wouldn’t be. When we say “It’s going to depend,” it’s not a dodge or an excuse, it’s a fact. AMD’s IDF showcase gave some additional information but not enough to change this basic situation.

How do you eat an elephant?

One of the common arguments raised in the Ashes of the Singularity benchmark thread was that Zen’s comparatively weak performance compared with the Core i7-5960X is proof that AMD’s eight-core chip won’t be able to compete against Intel. The simple fact that these test results were run on an ES chip of unknown stepping and vintage make that an extremely premature conclusion. Worse, it’s a conclusion founded in an incorrect premise — specifically, that AMD has to match Intel’s top-end performance in order to compete at all. While AMD’s recent demos should assuage some of these fears, the early unveil wasn’t meant to be a complete overview of every aspect of the chip’s performance.
Right now, AMD’s FX-8350 is a $160 CPU, while the top-end FX-9590 retails for $229. Intel’s quad-core Core i5 desktop processors start at $185 for older Haswell parts and $190 for Skylake. The cheapest Core i7 you can buy starts at $295 for Haswell and $305 for Skylake (all prices from NewEgg). This means the FX-8350 is priced against a high-end Skylake Core i3 (the Core i3-6320) while the FX-9590 faces off against the Core i5-6600 — a comparatively tiny chip with an integrated GPU and one-third the TDP.
In the 15 years I’ve been reviewing CPUs, the gap between AMD and Intel has never been larger than it is today. That’s part of why Zen is so important, but it’s also why it’s important to keep perspective on what kind of performance improvement AMD can reasonably deliver in a single product cycle.
Based on AMD’s single 40% IPC figure, it’s extremely unlikely that the company will deliver a CPU that can match Intel’s performance at every particular and at every price point — and it doesn’t need to. A 40% IPC boost would allow AMD to challenge Intel’s Core i3/i5/i7 line-up by leveraging larger core counts and its own SMT implementation far more effectively than Piledriver ever did. The drastically reduced TDP (Zen has reportedly targeted 95W at the high end) will allow it to compete much more aggressively on power consumption. Higher CPU efficiency means that AMD won’t need to rely on high clocks to hit performance targets, making it easier to push into laptops when Zen-based APUs come to market. Trade-offs between core count and clock speed also mean AMD can probably offer lower core counts at higher clocks, the same way that Intel does.
It’s easy to forget, but AMD didn’t launch K7 in 1999 and seize 20% of the server market 12 months later. K7 was competitive with the Pentium 3, but not necessarily faster — particularly since Intel’s Coppermine P3’s ran a full-speed L2 cache while the slot-based K7 and K7.5 used a half-speed or 1/3 speed L2. Socket A and Thunderbird closed this gap in June 2000, but AMD didn’t enter the server market until 2001. It didn’t see serious success in the server market until 2003, when K8 gave it the legs it needed to go head-to-head with Intel’s high-end Xeons.
Right now, Intel’s least expensive eight-core processor is the Core i7-5960X, at $1,015. AMD doesn’t need to hit Intel in the $1,000 CPU market to drastically improve its own fortunes or competitive standing.

Conclusion

Zen will be judged a failure or a success based on how well it performs today and on how well it positions AMD to deliver future improvements. It may not going to be strong enough to go toe-to-toe with Skylake across every SKU and price point, but that’s not what it needs to do. AMD needs Zen to perform well at low power so it can be paired with an APU and slipped into notebooks. It needs Zen to be more efficient than Excavator so Sunnyvale isn’t left pricing eight-core chips against Intel’s Core i3. And it needs Zen to be strong enough that investors and enthusiasts see the core as a future to be built upon, rather than an anchor around the company’s neck.
I genuinely don’t know how well AMD will deliver on these goals. But those are the criteria I expect the chip to need to fulfill and the metrics by which I’ll judge its overall position. I’ll have more to say about Zen, including a deep dive into its architecture, when I return next week.
Hybrid system designed to harvest 'full spectrum' of solar energy

Hybrid system designed to harvest 'full spectrum' of solar energy


                                                                   
Hybrid system designed to harvest 'full spectrum' of solar energy
This schematic depicts a new concept that could bring highly efficient solar power by combining three types of technologies that convert different parts of the light spectrum and also store energy for use after sundown. Credit: Purdue University image/Peter Bermel
A new concept could bring highly efficient solar power by combining three types of technologies that convert different parts of the light spectrum and also store energy for use after sundown.
Combining the technologies could make it possible to harness and store far more of the spectrum of sunlight than is possible using any one of the technologies separately.
"Harvesting the full spectrum of sunlight using a hybrid approach offers the potential for higher efficiencies, lower power production costs, and increased power grid compatibility than any single technology by itself," said Peter Bermel, an assistant professor in Purdue University's School of Electrical and Computer Engineering. "The idea is to use technologies that, for the most part exist now, but to combine them in a creative way that allows us to get higher efficiencies than we normally would."
The approach combines , which convert visible and ultraviolet light into electricity, that convert heat into electricity, and steam turbines to generate electricity. The thermoelectric devices and steam turbines would be driven by heat collected and stored using mirrors to focus sunlight onto a newly designed "selective solar absorber and reflector."
"This is a spectrally selective system, so it is able to efficiently make use of as much of the spectrum as possible," he said. "The thermal storage allows for significant flexibility in the time of power generation, so the system can produce power for hours after sunset, providing a consistent source of throughout the day."
Findings from the research are detailed in a paper with an advance online publication date of Aug. 15, and the paper is scheduled to appear in a future print issue of the journal Energy & Environmental Science.
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The hybrid system is designed to meet the changing demands for electricity at different times of the day.
"Typically for U.S. households, you have low usage overnight, then the demand goes up substantially in the morning, drops off a little during the day and then spikes upward around 5 p.m.," Bermel said. "Photovoltaics match very well with the load during the day, but not when it spikes. So the idea is to store energy just for a few hours, and that helps you address times of spiking demand."
Ideally, the system could achieve efficiencies of more than 50 percent using realistic materials, compared to 31 percent for photovoltaic cells alone.
The new selective solar absorber and reflector is the lynchpin of this approach and would perform two crucial roles: increase efficiency by reflecting visible light but absorbing near-infrared photons, and increase the temperature of the stored heat, which is then harnessed as electricity when it is needed throughout the course of the day.
Experimental research is still required to validate the theoretical design of the overall system.
"I think that this hybrid approach is doable," Bermel said. "In principle, we understand what needs to be done, but we need to do the experiments to validate the components and the whole system together."

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