The AMD Zen and Ryzen 7 Review: A Deep Dive on 1800X, 1700X and 1700
by Ian Cutress on March 2, 2017 9:00 AM ESTSimultaneous MultiThreading (SMT)
Zen will be AMD’s first foray into a true simultaneous multithreading structure, and certain parts of the core will act differently depending on their implementation. There are many ways to manage threads, particularly to avoid stalls where one thread is blocking another that ends in the system hanging or crashing. The drivers that communicate with the OS also have to make sure they can distinguish between threads running on new cores or when a core is already occupied – to achieve maximum throughput then four threads should be across two cores, but for efficiency where speed isn’t a factor, perhaps power gating/clock gating half the cores in a CCX is a good idea.
There are a number of ways that AMD will deal with thread management. The basic way is time slicing, and giving each thread an equal share of the pie. This is not always the best policy, especially when you have one performance dominant thread, or one thread that creates a lot of stalls, or a thread where latency is vital. In some methodologies the importance of a thread can be tagged or determined, and this is what we get here, though for some of the structures in the core it has to revert to a basic model.
With each thread, AMD performs internal analysis on the data stream for each to see which thread has algorithmic priority. This means that certain threads will require more resources, or that a branch miss needs to be prioritized to avoid long stall delays. The elements in blue (Branch Prediction, INT/FP Rename) operate on this methodology.
A thread can also be tagged with higher priority. This is important for latency sensitive operations, such as a touch-screen input or immediate user input elements required. The Translation Lookaside Buffers work in this way, to prioritize looking for recent virtual memory address translations. The Load Queue is similarly enabled this way, as typically low latency workloads require data as soon as possible, so the load queue is perfect for this.
Certain parts of the core are statically partitioned, giving each thread an equal timing. This is implemented mostly for anything that is typically processed in-order, such as anything coming out of the micro-op queue, the retire queue and the store queue. However, when running in SMT mode but only with a single thread, the statically partitioned parts of the core can end up as a bottleneck, as they are idle half the time.
The rest of the core is done via competitive scheduling, meaning that if a thread demands more resources it will try to get there first if there is space to do so each cycle.
New Instructions
AMD has a couple of tricks up its sleeve for Zen. Along with including the standard ISA, there are a few new custom instructions that are AMD only.
Some of the new commands are linked with ones that Intel already uses, such as RDSEED for random number generation, or SHA1/SHA256 for cryptography (even with the recent breakthrough in security). The two new instructions are CLZERO and PTE Coalescing.
The first, CLZERO, is aimed to clear a cache line and is more aimed at the data center and HPC crowds. This allows a thread to clear a poisoned cache line atomically (in one cycle) in preparation for zero data structures. It also allows a level of repeatability when the cache line is filled with expected data. CLZERO support will be determined by a CPUID bit.
PTE (Page Table Entry) Coalescing is the ability to combine small 4K page tables into 32K page tables, and is a software transparent implementation. This is useful for reducing the number of entries in the TLBs and the queues, but requires certain criteria of the data to be used within the branch predictor to be met.
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deltaFx2 - Wednesday, March 8, 2017 - link
@Meteor2: No. Consumer GPUs have poor throughput for Double precision FP. So you can't push those to the GPU (unless you own those super-expensive Nvidia compute cards). Apparently, many rendering/video editing programs use GPUs for preview but do the final rendering on CPU. Quality, apparently, and might be related to DP FP. I'm not the expert, so if you know otherwise, I'd be happy to be corrected and educated. Also, you could make the same argument about AVX-256.The quoted paragraph is probably the only balanced statement in that entire review. Compare the tone of that review with AT review above.
On an unrelated note, there's the larger question of running games at low res on top-end gpus and comparing frame-rates that far exceed human perception. I know, they have to do something, so why not just do this. The rationale is: " In future a faster GPU in future will create a bottleneck ". If this is true, it should be easy to demonstrate, right? Just dig through a history of Intel desktop CPUs paired with increasingly powerful GPUs and see how it trends. There's not one reviewer that has proven that this is true. It's being taken as gospel. OTOH, plenty of folks seem happy with their Sandy Bridge + Nvidia 1080, so clearly the bottleneck isn't here 5 years after SB. Maybe, just maybe, it's because the differences are imperceptible?
Ryzen clearly has some bottlenecks but the whole gaming thing is a tempest in a tea-cup.
theuglyman0war - Thursday, March 9, 2017 - link
ZBRUSHprobably 90% of all 3d assets that are created from concept ( NOT SCANNED )
Went through Zbrush at some point.
Which means no GPU acceleration at all.
Renderman
Maxwell
Vray
Arnold
still all use CPU rendering As do a mountain of other renderers.
Arnold will be getting an option
But the two popular GPU renderers are Otoy Octane and Redshift...
The have their excellent expensive place. But the majority of rendering out there is still suffered through software rendering. And will always be a valid concern as long as they come FREE built into major DCC applications.
theuglyman0war - Thursday, March 9, 2017 - link
Saw that same GPU trumps CPU render validity concerns...Comment and had a good laugh.
I'll remember to spread that around every time I see Renderman Vray Arnold Maxwell sans GPU rendering going on.
Or the next time a Mercury engine update negates all non Quadro GPU acceleration.
To be fair a lot of creative pros and tech artists seem to disagree with me but...
The only time between pulling vrts in Maya and brushing a surface in Zbrush that I really feel that I am suffering buckets of tears and desire a new CPU ( still on i7-980x ) is when I am cussing out a progress bar that is teasing me with it's slow progress. And that means CORES! encoding... un compressing... Rendering! Otherwise I could probably not notice day to day on a ten year old CPU. ( excluding CPU bound gaming of course... talking bout day to day vrt pulling )
I was just as productive in 2007 as I am today.
MaidoMaido - Saturday, March 4, 2017 - link
Been trying to find a review including practical benchmarks for common video editing / motion graphics applications like After Effects, Resolve, Fusion, Premiere, Element 3D.In a lot of these tasks, the multithreading is not always the best, as a result quad core 6700K often outperforms the more expensive Xeon and 5960X etc
deltaFx2 - Saturday, March 4, 2017 - link
I would recommend this response to the GamersNexus hit piece: https://www.reddit.com/r/Amd/comments/5xgonu/analy...The i5 level performance is a lie.
Notmyusualid - Saturday, March 4, 2017 - link
@ deltaFx2Sorry, not reading a 4k worded response. I'll wait for Anand to finish its Ryzen reviews before I draw any final conclusions.
Meteor2 - Tuesday, March 7, 2017 - link
@deltaFX2 RE: in the 4k word Reddit 'rebuttal', what that person seems to be saying, is that once you've converted your $500 Ryzen 1800X into a 8C/8T chip, _then_ it beats a $240 i5, while still falling short of the $330 i7. Out-of-the-box, it has worse gaming performance than either Intel chip.That's not exactly a ringing endorsement.
The analysis in the Anandtech forums, which concludes that in a certain narrow and low power band a heavily down-clocked 1800X happens to get excellent performance/W, isn't exactly thrilling either.
deltaFx2 - Wednesday, March 8, 2017 - link
@ Meteor2: The anandtech forum thing: Perf/watt matters for servers and laptop. Take a look at the IPC numbers too. His average is that Zen == Broadwell IPC, and ~10% behind Sky/Kaby lake (except for AVX256 workloads). That's not too shabby at all for a $300 part.You completely missed the point of the reddit rebuttal. The GN reviewer drops i5s from plenty of tests citing "methodological reasons", but then says R7==i5 in gaming. The argument is that plenty of games use >4 threads and that puts i5 at a disadvantage.
tankNZ - Sunday, March 5, 2017 - link
yes I agree, it's even better than okay for gaming[img]http://smsh.me/li3a.png[/img]deltaFx2 - Monday, March 6, 2017 - link
You may wish to see this though: https://forums.anandtech.com/threads/ryzen-strictl... Way, way, more detailed than any tech media review site can hope to get. No, it's got nothing to do with gaming. Gaming isn't the story here. AMD's current situation in x86 market share had little to do with gaming efficiency, but perf/watt.I'll quote the author: "850 points in Cinebench 15 at 30W is quite telling. Or not telling, but absolutely massive. Zeppelin can reach absolutely monstrous and unseen levels of efficiency, as long as it operates within its ideal frequency range."