The AMD Ryzen Threadripper 1950X and 1920X Review: CPUs on Steroids
by Ian Cutress on August 10, 2017 9:00 AM ESTFeeding the Beast
When frequency was all that mattered for CPUs, the main problem became efficiency, thermal performance, and yields: the higher the frequency was pushed, the more voltage needed, the further outside the peak efficiency window the CPU was, and the more power it consumed per unit work. For the CPU that was to sit at the top of the product stack as the performance halo part, it didn’t particularly matter – until the chip hit 90C+ on a regular basis.
Now with the Core Wars, the challenges are different. When there was only one core, making data available to that core through caches and DRAM was a relatively easy task. With 6, 8, 10, 12 and 16 cores, a major bottleneck suddenly becomes the ability to make sure each core has enough data to work continuously, rather than waiting at idle for data to get through. This is not an easy task: each processor now needs a fast way of communicating to each other core, and to the main memory. This is known within the industry as feeding the beast.
Top Trumps: 60 PCIe Lanes vs 44 PCIe lanes
After playing the underdog for so long, AMD has been pushing the specifications of its new processors as one of the big selling points (among others). Whereas Ryzen 7 only had 16 PCIe lanes, competing in part against CPUs from Intel that had 28/44 PCIe lanes, Threadripper will have access to 60 lanes for PCIe add-in cards. In some places this might be referred to as 64 lanes, however four of those lanes are reserved for the X399 chipset. At $799 and $999, this competes against the 44 PCIe lanes on Intel’s Core i9-7900X at $999.
The goal of having so many PCIe lanes is to support the sort of market these processors are addressing: high-performance prosumers. These are users that run multiple GPUs, multiple PCIe storage devices, need high-end networking, high-end storage, and as many other features as you can fit through PCIe. The end result is that we are likely to see motherboards earmark 32 or 48 of these lanes for PCIe slots (x16/x16, x8/x8/x8/x8, x16/x16/x16, x16/x8/x16/x8), followed by a two or three for PCIe 3.0 x4 storage via U.2 drives or M.2 drives, then faster Ethernet (5 Gbit, 10 Gbit). AMD allows each of the PCIe root complexes on the CPU, which are x16 each, to be bifurcated down to x1 as needed, for a maximum of 7 devices. The 4 PCIe lanes going to the chipset will also support several PCIe 3.0 and PCIe 2.0 lanes for SATA or USB controllers.
Intel’s strategy is different, allowing 44 lanes into x16/x16/x8 (40 lanes) or x16/x8/x16/x8 (40 lanes) or x16/x16 to x8/x8/x8x8 (32 lanes) with 4-12 lanes left over for PCIe storage or faster Ethernet controllers or Thunderbolt 3. The Skylake-X chipset then has an additional 24 PCIe lanes for SATA controllers, gigabit Ethernet controllers, SATA controllers and USB controllers.
Top Trumps: DRAM and ECC
One of Intel’s common product segmentations is that if a customer wants a high core count processor with ECC memory, they have to buy a Xeon. Typically Xeons will support a fixed memory speed depending on the number of channels populated (1 DIMM per channel at DDR4-2666, 2 DIMMs per channel at DDR4-2400), as well as ECC and RDIMM technologies. However, the consumer HEDT platforms for Broadwell-E and Skylake-X will not support these and use UDIMM Non-ECC only.
AMD is supporting ECC on their Threadripper processors, giving customers sixteen cores with ECC. However, these have to be UDIMMs only, but do support DRAM overclocking in order to boost the speed of the internal Infinity Fabric. AMD has officially stated that the Threadripper CPUs can support up to 1 TB of DRAM, although on close inspection it requires 128GB UDIMMs, which max out at 16GB currently. Intel currently lists a 128GB limit for Skylake-X, based on 16GB UDIMMs.
Both processors run quad-channel memory at DDR4-2666 (1DPC) and DDR4-2400 (2DPC).
Top Trumps: Cache
Both AMD and Intel use private L2 caches for each core, then have a victim L3 cache before leading to main memory. A victim cache is a cache that obtains data when it is evicted from the cache underneath it, and cannot pre-fetch data. But the size of those caches and how AMD/Intel has the cores interact with them is different.
AMD uses 512 KB of L2 cache per core, leading to an 8 MB of L3 victim cache per core complex of four cores. In a 16-core Threadripper, there are four core complexes, leading to a total of 32 MB of L3 cache, however each core can only access the data found in its local L3. In order to access the L3 of a different complex, this requires additional time and snooping. As a result there can be different latencies based on where the data is in other L3 caches compared to a local cache.
Intel’s Skylake-X uses 1MB of L2 cache per core, leading to a higher hit-rate in the L2, and uses 1.375MB of L3 victim cache per core. This L3 cache has associated tags and the mesh topology used to communicate between the cores means that like AMD there is still time and latency associated with snooping other caches, however the latency is somewhat homogenized by the design. Nonetheless, this is different to the Broadwell-E cache structure, that had 256 KB of L2 and 2.5 MB of L3 per core, both inclusive caches.
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Ian Cutress - Thursday, August 10, 2017 - link
Anand hasn't worked at the website for a few years now. The author (me) is clearly stated at the top.Just think about what you're saying. If I was in Intel's pocket, we wouldn't be being sampled by AMD, period. If they were having major beef with how we were reporting, I'd either be blacklisted or consistently on a call every time there's been an AMD product launch (and there's been a fair few this year).
I've always let the results do the talking, and steered clear from hype generated by others online. We've gone in-depth into the how things are done the way they are, and the positives and negatives as to the methods of each action (rather than just ignoring the why). We've run the tests, and been honest about our results, and considered the market for the product being reviewed. My background is scientific, and the scientific method is applied rigorously and thoroughly on the product and the target market. If I see bullshit, I point it out and have done many times in the past.
I'm not exactly sure what you're problem is - you state that the review is 'slanted journalism', but fail to give examples. We've posted ALL of our review data that we have, and we have a benchmark database for anyone that ones to go through all the data at any time. That benchmark database is continually being updated with new CPUs and new tests. Feel free to draw your own conclusions if you don't agree with what is written.
Just note that a couple of weeks ago I was being called a shill for AMD. A couple of weeks before that, a shill for Intel. A couple before that... Nonetheless both companies still keep us on their sampling lists, on their PR lists, they ask us questions, they answer our questions. Editorial is a mile away from anything ad related and the people I deal with at both companies are not the ones dealing with our ad teams anyway. I wouldn't have it any other way.
MajGenRelativity - Thursday, August 10, 2017 - link
I personally always enjoy reading your reviews Ian. Even though they don't always reach the conclusions I hoped they would reach before reading, you have the evidence and benchmarks to back it up. Keep up the good work!Diji1 - Thursday, August 10, 2017 - link
Agreed!Zstream - Thursday, August 10, 2017 - link
For me, it isn't about "scientific benchmarking", it's about what benchmarks are used and what story is being told. I think, along with many others, would never buy a threadripper to open a single .pdf. I could be wrong, but I don't think that's the target audience Intel or AMD is aiming for.I mean, why not forgo the .pdf and other benchmarks that are really useless for this product and add multi-threaded use cases. For instance, why not test how many VM's and I/O is received, or launching a couple VM's, running a SQL DB benchmark, and gaming at the same time?
It could just be me, but I'm not going to buy a 7900x or 1950x for opening up .pdf files, or test SunSpider/Kraken lol. Hopefully we didn't include those benchmarks to tell a story, as mentioned above.
We're goingto be compiling, 3d rendering with multi-gpu's, running multiple VM's, all while multi-tasking with other apps.
My 2 cents.
DanNeely - Thursday, August 10, 2017 - link
Single threaded use cases aren't why people buy really wide CPUs. But performing badly in them, since they represent a lot of ordinary basic usage, can be a reason not to buy one. Also running the same benches on all products allows for them all to be compared readily vs having to hunt for benches covering the specific pair you're interested in.VM type benchmarks are more Johan's area since that's a traditional server workload. OTOH there's a decent amount of overlap with developer workloads there too so adding it now that we've got a compile test might not be a bad idea. On the gripping hand, any new benchmarks need to be fully automated so Ian can push an easy button to collect data while he works on analysis of results. Also the value of any new benchmark needs to be weighed against how much it slows the entire benching run down, and how much time rerunning it on a large number of existing platforms will take to generate a comparison set.
iwod - Thursday, August 10, 2017 - link
It really depends on use case. 20% slower on PDF opening? I dont care, because the time has reached diminishing returns and Intel needs to be MUCH faster for this to be a UX problem.But I think at $999 Intel has a strong case for its i9. But factoring in the MB AMD is still cheaper. Not sure if that is mentioned in the article.
Also note Intel is on their third iteration of 14nm, against a new 14nm from AMD GloFlo.
I am very excited for 7nm Zen 2 coming next year. I hope all the software and compiler as well as optimisation has time to catch up for Zen.
Zstream - Thursday, August 10, 2017 - link
I won't get into an argument, but I and many of my friends, who are on the developer side of the house have been waiting for this review, and it doesn't provide me with any useful information. I understand it might be Johan's wheelhouse, but come on... opening a damn .pdf file, and testing SunSpider/Kraken/gaming benchmarks? That won't provide anyone interested in either CPU any validation of purchase. I'm not trying to be salty, I just want some more damn details vs. trying to put both vendors in a good light.Ian Cutress - Thursday, August 10, 2017 - link
Rather than have 20 different tests for each set of different CPUs and very minimal overlap, we have a giant glove that has all the tests for every CPU in a single script. So 80 test points, rather than 4x20. The idea is that there are benchmarks for everyone, so you can ignore the ones that don't matter, rather than expect 100% of the benchmarks to matter (e.g. if you care about five tests, does it matter to you if the tests are published alongside 75 other tests, or do they have to be the only five tests in the review?). It's not a case of trying to put both vendors in a good light, it's a case of this is a universal test suite.Zstream - Thursday, August 10, 2017 - link
Well, show me a database benchmark, virtual machine benchmark, 3dmax benchmark, blender benchmark and I'll shutty ;)It's hard for me to look at this review outside of a gamers perspective, which I'm not. Sorry, just the way I see it. I'll wait for more pro-consumer benchmarks?
Johan Steyn - Thursday, August 10, 2017 - link
This is exactly my point as well. Why on earth so much focus on single threaded tests and games, since we all knew from way back TR was not going to be a winner here. Where are all the other benches as you mention. Oh, no, this will have Intel look bad!!!!!