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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BurntMyBacon - Friday, March 3, 2017 - link
@Gothmoth: "gamer... as if the world is only full with idiotic people who waste their lives playing shooter or RPG´s."PC Gaming happens to be one of the few growing areas in the PC market. Not everyone games, but for those that do, the 7700K is still worth considering. Dropping $500 on the 1800X may not be the best call for those that don't take advantage of the parallelism. Of course, the 1800X wasn't really meant for people who can't take advantage of the parallelism. AMD will have lower cost narrower processors to address that gap. I'm curious as to how the performance/price equation will stand once AMD releases their upper end 6c/12t and 4c/8t processors.
Beany2013 - Friday, March 3, 2017 - link
Sod the 1800X - I need a new VM server, and if I want all the threads (sixteen), I can either drop £450 on a Xeon E5 2620 at 2.1-3ghz (cheapest Intel 16 thread option I can find), or I can spend £100 less, and get a Ryzen 7 1700 (3.0-3.7ghz) and put that extra money towards more RAM so I can run more VMs and get more work done.For those of us who aren't high end gamers - which is basically almost everyone, and a far more significant market - these chips may well give Intel a bloody nose in the workstation space; AMD have confirmed they'll use ECC RAM quite happily.
Photographers, videographers, CAD-CAM, developers etc are a bigger market in terms of raw units than high end gamers, and these chips look like being a pretty compelling option as it stands.
Steven R
Beany2013 - Friday, March 3, 2017 - link
(VM server for home, I should have noted - for work, I'll see how the Ryzen based opterons and supermicro mobos etc pan out - money is important in these factors, but I'm not a moron, and I'm not going to run production gear on gaming hardware, natch....)BurntMyBacon - Friday, March 3, 2017 - link
@Beany2013: "I need a new VM server, and if I want all the threads (sixteen), I can either drop £450 on a Xeon E5 2620 at 2.1-3ghz (cheapest Intel 16 thread option I can find), or I can spend £100 less, and get a Ryzen 7 1700 (3.0-3.7ghz) and put that extra money towards more RAM so I can run more VMs and get more work done."It is clear by this statement that you fall into the category of people that can take advantage of the parallelism. Therefore, my statement doesn't apply to your presented in the slightest.
I don't disagree that the Ryzen 7 series has a lot to offer to a lot of people (myself included). If I were in the market today, I'd be looking long and hard at an R7 1700X. The minor drop in gaming performance is less significant to me than the increase in performance for many other tasks I use my computer for. I do a little bit of dabbling in a lot of different things (most of which benefit from high thread count). I have noticed that for the set of applications I have open simultaneously and the tasks I have running, my computer is more responsive with more cores or threads, but single threaded performance is still important to the individual tasks.
In my workflow: (i3 < i5/FX-8xxx < i7 <? R7)
My point was that there is in fact a not so insignificant market of people putting computers together for the primary purpose of gaming. This market appears, by all metrics, to be growing. For this market, Intel's i7-7700K or better yet i5-7600K are still viable options that provide better performance/price than AMD's current options. I'll repeat: "AMD will have lower cost narrower processors to address that gap. I'm curious as to how the performance/price equation will stand once AMD releases their upper end 6c/12t and 4c/8t processors."
Cooe - Sunday, February 28, 2021 - link
"or better yet i5-7600K"Arguably the most short-sited statement in this entire comments section lol. The 4c/4t i5's had roughly equal gaming performance to Ryzen at launch but with ZERO headroom left for the future. This is why the i5-7600K gets absolutely freaking ROFLSTOMPED by the R5 1600 in modern titles/game engines.
JMB1897 - Friday, March 3, 2017 - link
Compelling, but I don't think it's totally there yet. I'd be worried about the memory issues. Increased latency as you add more DIMMs and dual vs quad channel. I'd spend that extra 100 on a Xeon personally.Sttm - Friday, March 3, 2017 - link
Thats who buys off the shelf CPUs thats cost $$$, Gamers. Thats who AMD needs to please with their product. GAMERS. Thats why AMD's stock has been tanking since Ryzen reviews went up, because GAMERS are the demographic that matters when it comes to performance CPU sales.deltaFx2 - Saturday, March 4, 2017 - link
@Sttm: You have an inflated opinion of the impact of gamers. No, AMD's stock isn't tanking because of gamers. I suggest you also look at Nvidia's stock, which is well down from its high of ~120, to ~98. Wed-Friday, Nvidia dropped from 105 to 98, and it dipped below that to ~96 at one point. That's roughly 7-8%. The two stocks are often correlated on drops, with AMD amplifying nvidia's drop. Both do GPUs, see? Some people make tonnes of money shorting AMD (and in recent times have lost their shirt doing so).Here's the truth: All Desktop, as per Lisa Su, is a 5 bn TAM market and gaming is part of this (let's say 50%). Nothing to scoff at, sure, but compared to laptop and server, it's a rounding error. There's NOTHING in these tests/reviews to suggest that AMD will suck in those markets; in fact, quite the opposite: power looks good, perf looks good. AMD's stock (long term) won't tank on the whims of gamers. They help get the mindshare, which is the only reason they're worth catering to (they tend to be a vocal, passionate, and sometimes irrational lot. You won't see datacenter gurus doing the stuff that gamers do. They certainly won't shoot each other over whose GPU is the best).
cmdrdredd - Saturday, March 4, 2017 - link
Believe it or not there are millions of people worldwide who pretty much use their PC for two things. The internet (web browsing, email etc) and gaming. You don't need 16 threads to check email and read forums either so gaming performance is going to be critical. It's not just the CPU performance, it's the entire platform that contributes to Gaming related performance.sans - Thursday, March 2, 2017 - link
Yeah, stick with Intel because Intel is the standard and its products are the best for each respective market. AMD is a total failure.