Assessing Cavium's ThunderX2: The Arm Server Dream Realized At Last
by Johan De Gelas on May 23, 2018 9:00 AM EST- Posted in
- CPUs
- Arm
- Enterprise
- SoCs
- Enterprise CPUs
- ARMv8
- Cavium
- ThunderX
- ThunderX2
Single-Threaded Integer Performance: SPEC CPU2006
Getting down to measuring actual compute performance, we'll start with the SPEC CPU2006 suite. Astute readers will point out that SPEC CPU2006 is now outdated as SPEC CPU2017 has arrived. But due to the limited testing time and the fact that we could not retest the ThunderX, we decided to stick with CPU2006.
Given that SPEC is almost as much of a compiler benchmark as it is a hardware benchmark, we believe it's important to lay out our testing philosophy here. In this case, that using specific flags and other compiler settings just to inflate a benchmark's score does not lead to meaningful comparisons. So we want to keep the settings as "real world" as possible with the following settings (and we welcome constructive criticism on the matter):
- 64 bit gcc: most used compiler on Linux, good all round compiler that does not try to "break" benchmarks (libquantum...)
- -Ofast: compiler optimization that many developers may use
- -fno-strict-aliasing: necessary to compile some of the subtests
- base run: every subtest is compiled in the same way.
The first objective is to measure performance in applications where for some reason – as is frequently the case – a "multi-threading unfriendly" task keeps us waiting. Our second objective is to understand how well the ThunderX OOO architecture deals with a single thread compared to Intel's Skylake architecture. Keep in mind that this specific model Skylake chip can boost to 3.8 GHz. The chip will run at 2.8 GHz in almost all situations (28 threads active), and will sustain 3.4 GHz with 14 active threads.
Overall, Cavium positions the ThunderX2 CN9980 ($1795) as being "better than the 6148" ($3072), a CPU that runs at 2.6 GHz (20 threads) and reaches 3.3 GHz without much trouble (up to 16 threads active). As a result, the Intel SKUs will have a sizable 30% clock advantage in many situations (3.3GHz vs 2.5GHz).
Cavium makes up for this clockspeed deficit by offering up to 60% more cores (32 cores) than the Xeon 6148 (20 cores). But we must note that higher core counts will result in diminishing returns in many applications (e.g. Amdahl). So if Cavium wants to threaten Intel's dominant position with the ThunderX2, each core needs to at least offer competitive performance on a clock-for-clock. Or in this case, the ThunderX2 should deliver at least 66% (2.5 vs 3.8) of the single threaded performance of the Skylake. If that is not the case, Cavium must hope that the 4-way SMT bridges the gap.
| SPEC CPU2006: Single-Threaded | |||||
| Subtest SPEC CPU2006 Integer |
Application Type | Cavium ThunderX 2 GHz gcc 5.2 |
Cavium ThunderX2 @2.5 GHz gcc 7.2 |
Xeon 8176 @3.8 GHz gcc 7.2 |
ThunderX2 vs Xeon 8176 |
| 400.perlbench | Spam filter | 8.3 | 20.1 | 46.4 | 43% |
| 401.bzip2 | Compression | 6.5 | 14 | 25 | 56% |
| 403.gcc | Compiling | 10.8 | 26.7 | 31 | 86% |
| 429.mcf | Vehicle scheduling | 10.2 | 44.5 | 40.6 | 110% |
| 445.gobmk | Game AI | 9.2 | 15.7 | 27.6 | 57% |
| 456.hmmer | Protein seq. analyses | 4.8 | 22.2 | 35.6 | 62% |
| 458.sjeng | Chess | 8.8 | 15.8 | 30.8 | 51% |
| 462.libquantum | Quantum sim | 5.8 | 76.4 | 86.2 | 89% |
| 464.h264ref | Video encoding | 11.9 | 26.7 | 64.5 | 49% |
| 471.omnetpp | Network sim | 7.3 | 26.4 | 37.9 | 70% |
| 473.astar | Pathfinding | 7.9 | 15.6 | 24.7 | 63% |
| 483.xalancbmk | XML processing | 8.4 | 27.7 | 63.7 | 43% |
Without having the opportunity to do any profiling on the ThunderX2, we must humbly admit that we have to speculate a bit based on what we have read so far about these benchmarks. Furthermore, since the ThunderX2 is running ARMv8 (AArch64) code and the Xeon runs x86-64 code, the picture gets even blurrier.
The pointer chasing benchmarks – XML processing (also large OoO buffers necessary) and Path finding – which typically depend on a large L3-cache to lower the impact of access latency, are the worst performing on the ThunderX2. We can assume that the higher latency of DRAM system is hurting performance.
The workloads where the impact of branch prediction is higher (at least on x86-64: a higher percentage of branch misses) – gobmk, sjeng, hmmer – are not top performers either on the ThunderX2.
It's also worth noting that perlbench, gobmk, hmmer, and the instruction part of h264ref are all known to benefit from the larger L2-cache (512 KB) of Skylake. We are only giving you a few puzzle pieces, but together they might help to make some educated guesses.
On the positive side, the ThunderX2 performs well on gcc, which runs mostly inside the L1 and L2-cache (thus relying on a low latency L2) and where the performance impact of the branch predictor is minimal. Overall the best subtest for the TunderX2 is mcf (vehicle scheduling in public mass transportation), which is known to miss the L1 data cache almost completely, relying a lot on the L2-cache, which is pretty fast on the ThunderX2. Mcf also demands quite a bit of memory bandwidth. Libquantum is the one with the highest memory bandwidth demand. The fact that Skylake offers rather mediocre single threaded bandwidth is probably also a reason why the ThunderX2 is so competitive on libquantum and mcf.
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imaheadcase - Wednesday, May 23, 2018 - link
I really think Anandtech needs to branch into different websites. Its very strange and unappealing to certain users to have business/consumer/random reviews/phone info all bunched together.Ever since anand actually left it really did venture into more a business/insider based website with random stuff thrown in. It is in no way a bad thing, its just like this review for instance would not appeal to %95 of readers normally. Everyone likes technology naturally that comes to this website, but its a fine line between talking about high end server components that are out of reach to people who just read the article on the mini-itx gaming motherboard. lol
Andrei Frumusanu - Wednesday, May 23, 2018 - link
You're always free to skip articles, nobody's forcing you to read it.boeush - Wednesday, May 23, 2018 - link
I guess he'd prefer the site content to be grouped in some manner roughly mirroring market segmentation. For instance: consumer, professional, enterprise, exotic/HPC. As opposed to jumbling everything together. Personally, I don't mind - but then, I'm not known for obsessive-compulsive organizing, either :)BurntMyBacon - Thursday, May 24, 2018 - link
Given the large differences in tech, focus, needs, and trends, I wouldn't mind breaking out Phones and perhaps servers into their own sections. I think there is more than enough overlap to keep consumer and professional desktop/laptop/workstation together, but that is entirely up to how deeply you want to divide things up. On the other hand, you'll want all of it to show up on the front page in some form, or it'll look like the site doesn't have much activity. Perhaps separate pipelines for each category could work. That all said, I don't really mind just skipping over articles that don't interest me. :)imaheadcase - Thursday, May 24, 2018 - link
Please, that is just lazy excuse. Even news websites have catagory based on the news you interested in. Anandtech literally had a review of a gaming motherboard then a high end server thing, and newz feed gets filled with phone and other news.name99 - Thursday, May 24, 2018 - link
God, you must REALLY hate Twitter then...I argue with Andrei a lot, but every so often he writes a sentence like "You're always free to skip articles, nobody's forcing you to read it" that makes me want to clap him on the back and say "yes, YOU get it" :-)
Threska - Sunday, May 27, 2018 - link
Taken to it's logical extreme the front page could be a dumping ground cesspool and the retort would be "you don't have to wade through any of it" which sounds witty but doesn't solve anything, but over time would lead to the predictable outcome of people leaving.imaheadcase - Sunday, May 27, 2018 - link
I do hate twitter, but because it has no valid purpose other than to get customer service done faster with companies because it reflects more on them because public venue. Its mostly just a rant inducing place, or a place that is basically just texting anyways since everyone just wants you to send a DM.The whole idea of saying "you are free to skip it" is kinda silly thing to say on the internet now. Especially since more and more you can filter things according to what you want. Not only that, but with the tight competition with views from tech websites its in best interest to have more options.
Even the layout of website never changed. I mean have you ever been to website without a adblocker on? They don't even advertise tech related stuff on it. Its just stupid clickbait stuff.
Keep in mind, this is not a complaint about articles itself, its just how they are posted. I love this site, been coming to it ever since i built first pc when i was a kid. But its focus is all over the place now vs years ago out what its posting. I'm half thinking one day i will see a review of electronic toothbrush then next day new CPU.
GreenReaper - Monday, June 4, 2018 - link
I'd be fine with that, as long as it was the best darn toothbrush in town!Threska - Sunday, May 27, 2018 - link
Accessing through RSS might be a better solution especially with a good reader. Just needs accurate tags to match.