AMD Zen 2 Microarchitecture Analysis: Ryzen 3000 and EPYC Rome
by Dr. Ian Cutress on June 10, 2019 7:22 PM EST- Posted in
- CPUs
- AMD
- Ryzen
- EPYC
- Infinity Fabric
- PCIe 4.0
- Zen 2
- Rome
- Ryzen 3000
- Ryzen 3rd Gen
Decode
For the decode stage, the main uptick here is the micro-op cache. By doubling in size from 2K entry to 4K entry, it will hold more decoded operations than before, which means it should experience a lot of reuse. In order to facilitate that use, AMD has increased the dispatch rate from the micro-op cache into the buffers up to 8 fused instructions. Assuming that AMD can bypass its decoders often, this should be a very efficient block of silicon.
What makes the 4K entry more impressive is when we compare it to the competition. In Intel’s Skylake family, the micro-op cache in those cores are only 1.5K entry. Intel increased the size by 50% for Ice Lake to 2.25K, but that core is coming to mobile platforms later this year and perhaps to servers next year. By comparison AMD’s Zen 2 core will cover the gamut from consumer to enterprise. Also at this time we can compare it to Arm’s A77 CPU micro-op cache, which is 1.5K entry, however that cache is Arm’s first micro-op cache design for a core.
The decoders in Zen 2 stay the same, we still have access to four complex decoders (compared to Intel’s 1 complex + 4 simple decoders), and decoded instructions are cached into the micro-op cache as well as dispatched into the micro-op queue.
AMD has also stated that it has improved its micro-op fusion algorithm, although did not go into detail as to how this affects performance. Current micro-op fusion conversion is already pretty good, so it would be interesting to see what AMD have done here. Compared to Zen and Zen+, based on the support for AVX2, it does mean that the decoder doesn’t need to crack an AVX2 instruction into two micro-ops: AVX2 is now a single micro-op through the pipeline.
Going beyond the decoders, the micro-op queue and dispatch can feed six micro-ops per cycle into the schedulers. This is slightly imbalanced however, as AMD has independent integer and floating point schedulers: the integer scheduler can accept six micro-ops per cycle, whereas the floating point scheduler can only accept four. The dispatch can simultaneously send micro-ops to both at the same time however.
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jamescox - Saturday, June 22, 2019 - link
You seem to just be trying to spread FUD. Also, you don’t seem to know how long a nanosecond is. The CCX to CCX latency can cause slower performance for some badly written or or badly optimized multithreaded code, but it is on such a fine scale that it would just effect the average frame rate. It isn’t going to cause stuttering as you describe.The stuttering you describe could be caused by a huge number of things. It could be the gpu or cpu thermally throttling due to inadequate cooling. If the gpu utilization goes down low, that could be due to the game using more memory than the gpu has available. That will slow to a crawl while assets are loaded across the pci express bus. So, if anyone is actually having this problem, check your temperatures, check your memory usage (both cpu and gpu), then maybe look for driver / OS issues.
playtech1 - Wednesday, June 12, 2019 - link
Good products and good prices.Knock-out blow though? I don't think so for the consumer and gaming space, as I can buy a 9900 today for a fairly small premium over the price of a 3800x and get basically the same performance.
The 12 and 16 core chips look more difficult for Intel to respond to though, given how expensive its HEDT line is (and I say that as an owner of a 7860x).
Atari2600 - Wednesday, June 12, 2019 - link
Yeah, power and thermals are not so important in consumer/game space.In server/HPC, Intel is in deep crap.
Phynaz - Wednesday, June 12, 2019 - link
Bahahaha. No.eva02langley - Thursday, June 13, 2019 - link
Phhh... are you ban from WCCFtech?Gastec - Wednesday, June 19, 2019 - link
I guess I'm neither consumer nor gamer with my i7-860 and GTX 670, G502, G110 and G13. I bought the Logitech G13 just to type better comments on Tweeter :PGastec - Wednesday, June 19, 2019 - link
I also turn OFF RGB whenever I can, anti-cosumerism and anti-social is written on my forehead and everyone is pointing at me on the woke streets.just4U - Thursday, June 13, 2019 - link
I'd say it's a substantial blow to Intel. One of the reasons I picked up a 2700x was the cooler, which is pretty damn good overall.. and the buy in was substantially lower. The 3700x-3800x will only add to that incentive with increased performance (most will likely not even notice..)Drop in the 12-16 core processors (provided there are no tradeoffs for those additional cores..) make the 9900k unappealing on all fronts. The 9700K was a totally unappealing product with it's 8c/8t package..already and after this launch won't make sense at all.
Gastec - Thursday, June 20, 2019 - link
Core i9-9900 I presume. Nowhere to be found for sale in Mordor. Only found one on Amazon.com for $439.99 reduced from $524.95, sold by "Intel" whomever that scammer is.Hamza12786 - Thursday, June 13, 2019 - link
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