AMD Zen Microarchitecture: Dual Schedulers, Micro-Op Cache and Memory Hierarchy Revealed
by Ian Cutress on August 18, 2016 9:00 AM ESTLow Power, FinFET and Clock Gating
When AMD launched Carrizo and Bristol Ridge for notebooks, one of the big stories was how AMD had implemented a number of techniques to improve power consumption and subsequently increase efficiency. A number of those lessons have come through with Zen, as well as a few new aspects in play due to the lithography.
First up is the FinFET effect. Regular readers of AnandTech and those that follow the industry will already be bored to death with FinFET, but the design allows for a lower power version of a transistor at a given frequency. Now of course everyone using FinFET can have a different implementation which gives specific power/performance characteristics, but Zen on the 14nm FinFET process at Global Foundries is already a known quantity with AMD’s Polaris GPUs which are built similarly. The combination of FinFET with the fact that AMD confirmed that they will be using the density-optimised version of 14nm FinFET (which will allow for smaller die sizes and more reasonable efficiency points) also contributes to a shift of either higher performance at the same power or the same performance at lower power.
AMD stated in the brief that power consumption and efficiency was constantly drilled into the engineers, and as explained in previous briefings, there ends up being a tradeoff between performance and efficiency about what can be done for a number of elements of the core (e.g. 1% performance might cost 2% efficiency). For Zen, the micro-op cache will save power by not having to go further out to get instruction data, improved prefetch and a couple of other features such as move elimination will also reduce the work, but AMD also states that cores will be aggressively clock gated to improve efficiency.
We saw with AMD’s 7th Gen APUs that power gating was also a target with that design, especially when remaining at the best efficiency point (given specific performance) is usually the best policy. The way the diagram above is laid out would seem to suggest that different parts of the core could independently be clock gated depending on use (e.g. decode vs FP ports), although we were not able to confirm if this is the case. It also relies on having very quick (1-2 cycle) clock gating implementations, and note that clock gating is different to power-gating, which is harder to implement.
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Reww - Friday, August 19, 2016 - link
Neither AMD or Intel invented the microprocessor, so they're both copying from someone. Now that we cleared that up, everyone can stfu about copying.BillBear - Saturday, August 20, 2016 - link
I will be thrilled to see AMD be competitive on more than price. If AMD is also competitive on performance it's a huge win for consumers.SlyNine - Saturday, August 20, 2016 - link
I almost expected Anand himself to come back and review this one.FireSnake - Monday, August 22, 2016 - link
Where did he go, anyway? Does anybody know?patel21 - Tuesday, August 23, 2016 - link
Some commenters say he is working for Apple nowJohan Steyn - Monday, August 22, 2016 - link
So many people here are defending Intel. Yes AMD has floundered. They have been poor competition to Intel. They are are struggling and maybe even a dying company. It will be a miracle if this chip will be successful, yet I do believe in miracles. I just hate having an Intel CPU in my notebook.Why is this so? Intel is the bully in town and they bullied AMD to death (almost). I have been in this business at that time. Companies were basically forced not to sell AMD. Intel was found guilty of it and got a slap on the wrist for it. $1B is nothing for them. For this I would welcome the day Intel dies a slow (make it rather quicker) and painful death. But this will probably not happen.
People say it it is just business, well it is in my books not ethical business even though it might be legal. It was even found to be illegal, yet with it they killed their opponent. These days many contractors do the same. When they build a building, the law requires a certain amount of parking space (in our country). If they do not do this, they are fined. Parking brings in little compensation and therefore they rather pay the fines, even if the fine are relatively high. This is what Intel did. They new they did wrong, but also new that the repercussions will be minimal. It was worth it for them to kill the competition by breaking the law and be fined. Intel might be your hero, not mine.
This is sickening. Intel makes me sick. I really hope AMD has some success with Zen, even though I think Intel will find another devious way to curb AMD's success. I even hope ARM will eventually dethrone Intel.
Outlander_04 - Monday, August 22, 2016 - link
AMD have surpassed intel in the past . Some of us are old enough to remember 1800 Mhz Athlon 64's smashing intel P4's running at 3000+ MHz .We also remember intels response that saw them bribe oems to continue using their crappy processors by sending back bags of cash to people still buying from them .
We also remember the fines and penalties intel eventually paid for their price fixing. Price fixing that cost their fanboys because it kept the prricee of theeir processors aartificiaally high eveen though they were junk .
A strong AMD is in everyones benefit . We will get more powerful processors and we will get them at a reasonable price . Lets hope ZEN is even better than it seems
sharath.naik - Tuesday, August 23, 2016 - link
The Problem with AMD is that being a technical company, they should have realized lying repeatedly in the name of marketing about the performance of their products, is akin to crying wolf. For now, it does not matter if they actually have a good product or not. The General assumption is that this is going to be another falsehood, and likely their chip can match intel at 3 ghz only when one core is running (That too when turbo is disabled on intel). And will fall far behind both in single and multithread when there is no trubo restriction on the intel chipslyronit - Tuesday, August 23, 2016 - link
I agree with you, but if there's something that can kill Intel at this point, it would be ARM based chips, not AMD.atomsymbol - Monday, August 22, 2016 - link
Bulldozer and Piledriver have a write-through L1D cache. Pentium4 has a write-through L1D cache. Zen has a write-back L1D cache. Skylake has a write-back L1D cache.