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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mapesdhs - Thursday, March 2, 2017 - link
It would be bizarre if they weren't clocked a lot higher, since there'll be a greater thermal limit per core, which is why the 4820K is such a fun CPU (high-TDP socket, 40 PCIe lanes, but only 4 cores so oc'ing isn't really limited by thermals compared to 6-core SB-E/IB-E) that can beat the 5820K in some cases (multi-GPU/compute).Meteor2 - Friday, March 3, 2017 - link
...Silverblue, look at the PDF opening test. What comes top? It's not an AMD chip.Cooe - Sunday, February 28, 2021 - link
Lol, because opening PDF's is where people need/will notice more performance? -_-CPU's have been able to open up PDF's fast enough to be irrelevant since around the turn of the century...
rarson - Thursday, March 2, 2017 - link
"AMD really isn't offering anything much for the mid range or regular desktop user either."So I'd HIGHLY recommend you wait 3 months, or overpay for Intel stuff. Because the lower-core Zen chips will no doubt provide the same performance-per-dollar that the high-end Ryzen chips are offering right now.
rarson - Thursday, March 2, 2017 - link
"their $499 CPU is often beaten by an i3."It's clear that you're looking at raw benchmark numbers and not real-world performance for what the chip is designed. If all you need is i3 performance, then why the hell are you looking at an 8-core processor that runs $329 or more?
Ratman6161 - Friday, March 3, 2017 - link
Its all academic to me. As I posted elsewhere, my i7-2600K is still offering me all the performance I need. So I'm just reading this out of curiosity. I also really, really want to like AMD CPU's because I still have a lot of nostalgia for the good old days of the Athlon 64 - when AMD was actually beating Intel in both performance and price. And sometimes I like to tinker around with the latest toys even if I don't particularly need it. I have a home lab with two VMWare ESXi systems built on FX-8320's because at the time they were the cheapest way to get to 8 threads - running a lot of VM's but with each VM doing light work.I also run an IT department so I'm always keeping tabs on what might be coming down the pike when I get ready to update desktops. But there is a sharp divide between what I buy for myself at home and what I buy for users at work. At work, most of our users actually would do fine with an i3. But I'm also keeping an eye out for what AMD has on offer in this range.
Notmyusualid - Tuesday, March 7, 2017 - link
@ Jimster480Sorry pal, but that is false, or inaccurate information.
ALL BUT the lowest model of CPUs in the 2011v3 platform are 40 PCIE lanes. Again, only the entry-level chip (6800K),has 28 lanes:
http://www.anandtech.com/show/10337/the-intel-broa...
But I do agree with you, that this is competing against the HEDT line.
Peace.
slickr - Thursday, March 2, 2017 - link
I'm sorry, but that sound just like Intel PR. I don't usually call people shills, but your reply seems to be straight out of Intel's PR book! First of all more and more games are taking advantage of more cores, you can easily see this especially with DX12 titles where if you have even 16 cores it will take advantage of.So having 8 cores for $330 to $500 is incredible value! We also see that the Ryzen chips are all competitive compared to the $1100 6900k which is where the comparison should be. Performance on 8 cores.
And as I've found out real world performance on 8 cores compared to 4 cores is like night and day. Have you tried running a demanding game, streaming in through OBS to Twitch, with the browser open to read Twitch chat and check other stuff in the process, while also having musicbee open and playing your songs and a separate program to read Twitch donations and text, etc...
This is where 4 core struggles a lot, while 8 core responsiveness is perfect. I can't use my PC if I decide to reduce a video size to a smaller one with a 4 core. Even 8 cores are fully taken advantage off, but through one core you can always do other stuff like watch movie or surf the internet without it struggling to process.
But even if games are your holy grail and what you base your opinion on, then Ryzen does really well. Its equal or slightly slower than the much much more optimized Intel processors. But you have to keep in mind a lot of the game code is optimized solely for Intel. That is what most gamers use, in fact over 80% is Intel based gamers, but developers will optimize for AMD now that they have a competitor on their hands.
We see this all the time, with game developers optimizing for RX 400 series a lot, even though Nvidia has the large majority of share in the market. So I expect to see anywhere from 10% to 25% more performance in games and programs that are also optimized for AMD hardware.
lmcd - Thursday, March 2, 2017 - link
How can you call someone a shill and post this without any self-awareness? Your real-world task is GPU-constrained anyway, since you should be using a GPU capable of both video encode and rendering simultaneously. If not, you can consider excellent features like Intel's Quick Sync, which works even with a primary GPU in use these days.Meteor2 - Friday, March 3, 2017 - link
Game code is optimised for x86.