AMD Zen Microarchitecture: Dual Schedulers, Micro-Op Cache and Memory Hierarchy Revealed
by Ian Cutress on August 18, 2016 9:00 AM ESTSimultaneous Multi-Threading
On Zen, each core will be able to support two threads in what is called ‘simulatenous multi-threading’. Intel has supported their version of SMT for a number of years, and other CPU manufacturers like IBM support up to 8 threads per core on their POWER8 platform designs. Building a core to be able to use multiple threads can be tough, as it requires a lot of resources to make sure that the threads do not block each other by consuming all the cache and buffers in play. But AMD will equip Zen with SMT which means we will see 8C/16T parts hitting the market.
Unlike Bulldozer, where having a shared FP unit between two threads was an issue for floating point performance, Zen’s design is more akin to Intel’s in that each thread will appear as an independent core and there is not that resource limitation that BD had. With sufficient resources, SMT will allow the core instructions per clock to improve, however it will be interesting to see what workloads will benefit and which ones will not.
Timeframe and Availability
At the presentation, it was given that Zen will be available in volume in 2017. As the AM4 platform will share a socket with Bristol Ridge, users are likely to see Bristol Ridge systems from AMD’s main OEM partners, like Dell and others, enter the market before separate Zen CPUs will hit the market for DIY builders. It’s a matter of principle that almost no consumer focused semiconductor company releases a product for the sale season, and Q1 features such events as CES, which gives a pretty clear indication of when we can expect to get our hands on one.
It’s worth noting that AMD said that as we get closer to launch, further details will come as well as deeper information about the design. It was also mentioned that the marketing strategy is also currently being determined, such that Zen may not actually be the retail product name for the line of processors (we already have Summit Ridge as the platform codename, but that could change for retail as well).
Wrap Up
AMD has gone much further into their core design than I expected this week. When we were told we had a briefing, and there were 200-odd press and analysts in the room, I was expecting to hear some high level puff about the brand and a reiteration of their commitment to the high end. To actually get some slides detailing parts of the microarchitecture, even at a basic cache level, was quite surprising and it somewhat means that AMD might have stolen the show with the news this week.
We’ve got another couple of pieces detailing some of the AMD internal/live benchmark numbers during the presentation, as well as the dual socket server platform, the 32-core Naples server CPU, and what we saw at the event in terms of motherboard design.
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breweyez - Friday, August 19, 2016 - link
You sure sound like an intel fanboysmilingcrow - Friday, August 19, 2016 - link
Recognising and acknowledging that AMD's CPUs were in the doldrums for 10 long years doesn't make you an Intel fanboy but a realist. Ignoring that inconvenient truth does though make you an AMD fanboy.Come on Zen although the amount of crap that the fanboys on both sides will spout when it is released will be immense. I will keep off the forums.
jjj - Friday, August 19, 2016 - link
There are no volumes above 350$, anything above that might as well not exist. Zen more or less needs to compete with Skylake while offering 2x the cores. If they have some higher clocks SKU above 350$, that could work but people need to be able to afford Zen,otherwise what's the point. Zen shouldn't be a huge die so AMD should be able to offer reasonable prices. Ofc there is no need to offer 8 cores high clocks at 200$ ,that's too far.BMNify - Friday, August 19, 2016 - link
if AMD cant get far better throughput than skylake with twice the zen cores , then they have no right to stay in business after all these missteps and the clammer of Jim Keller PR a DEC engineer who helped design the Alpha 21164 and 21264 processors then how can you ever expect to get a UHD1 rec.2020 capable CPU/GPU by even 2020.smilingcrow - Friday, August 19, 2016 - link
A lot of people are hoping that will be their strategy but it depends also on yields and final clock speeds.If they have low yields for the high clock speed parts they might well push that as an FX part and price it at $500 or more. It would still be a good halo product.
Also if they have a really good 8 core at $350 or under it will impact how much they can ask for the higher volume quad core parts.
If they sell too cheap they might have trouble matching the demand.
It's quite a juggling act to balance all that.
azazel1024 - Friday, August 19, 2016 - link
It sounds very good in fact. My biggest thing is overall system cost. Next is performance and finally noise and power consumption. Sure, I've love what a 10 core Core processor can level, but I don't really need it. I can get by with my Ivy Bridge i5-3570, but if I am going to upgrade, I'd like it to be for a nice boost in performance. Compared to my Ivy Bridge, I could be okay with a very small loss in single threaded performance, but I'd like a big gain in multithreaded performance. That to me says that Zen needs to bring, compared to my i5-3570, at least 90% single thread performance and at least 70-80% of the per core performance under multithreaded workloads. Then deliver it with roughly a $400 overall platform cost (between an "entry" mid-grade board and the CPU, ignoring RAM costs). Do that and they have a buyer from me. Don't and I'll probably look at the lowest level Hexacore Skylake-E processor once they come out next year.Basically I need 8 core Zen to be at least a little faster, averaged out, than current 6 core Broadwell-E, yet come in somewhat under the price of 6 core Broadwell-E. That would be enough extra performance to justify an upgrade from my current system early next year.
AndrewJacksonZA - Thursday, August 18, 2016 - link
I am disappointed that they are only releasing Zen in 2017 as I really am looking to upgrade my PC towards the end of the year. But hey, what's another few months, I guess? *siiiiiiiiiiiiiiigh*AndrewJacksonZA - Thursday, August 18, 2016 - link
Aaargh! Where's the edit button please guys????Just to be clear, I'm not waiting /to buy Zen/, I'm waiting for it to come out so that proper, independent tests can show what CPU would be better suited to my pocket and my needs.
melgross - Thursday, August 18, 2016 - link
As always, I've hopes that this will be what AMD says it will, but little confidence that it will.silverblue - Thursday, August 18, 2016 - link
The micro ops cache is a bit of a surprise; I believe the Steamroller preview mentioned that particular design was getting such a cache. Perhaps it didn't in the end.