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 Astute readers will point out that SPEC CPU2006 is now outdated as SPEC CPU2017 has arrived.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 - Sunday, May 27, 2018 - link
Yah i tried that for a bit, it worked ok. But was not foolproof, it missed some stuff.repoman27 - Wednesday, May 23, 2018 - link
Just to provide a counter point, this article made my day. And that’s coming entirely from intellectual curiosity—I don’t plan on deploying any servers with these chips in the near future. I always enjoy Johan’s writing, and was really looking forward to seeing how ThunderX2 would stack up. Many people are convinced that ARM is really only suitable in low power / mobile scenarios, but this is the chip that may finally prove otherwise. That has significant ramifications for the entire industry (including the consumer space), especially when you consider that Cavium could put out a TSMC 10nm or even 7nm shrink of ThunderX2 before Intel can get off of 14nm.HStewart - Wednesday, May 23, 2018 - link
This does not proved that ARM is suitable in higher end space - look at the core specific speed - it extremely low compare to Intel and AMD server chips. Keep in mind it takes 128 total cores - running at 4SMT system. And what about other operations - what about Virtual Machine situation - where you have many virtual x86 machines on VMWare server,How about high end mathematical and vector logic?
It does seem like ARM can run more threads - but maybe Intel or AMD has never had the need to
I think this latest Core battle is silly - I think it really not the number of cores you have but combination of type and speed of cores along with number of cores.
Wilco1 - Wednesday, May 23, 2018 - link
It certainly does prove that Arm can do high end servers - the results clearly show IPC/GHz is very close on SPECINT. Base clock speeds are the same as the Intel cores, and that's the speed the server runs at when not idle. But there are more cores as you say, so who will win is obvious.Now imagine a next-gen 7nm version before Intel manages 10nm. Not a pretty picture, right?
HStewart - Wednesday, May 23, 2018 - link
Ok I have learn to agree to disagree with some peopleCan this server run the VMWare server
https://kb.vmware.com/s/article/1003882
The answer is no - just one example - many more,
On 10nm - it not number that matters - it technology behind it - Intel supposely has a i3 and Y based for CannonLake coming this year - probably more.
Wilco1 - Wednesday, May 23, 2018 - link
There are plenty of VMs for Arm, so virtualization is not an issue.10nm will be behind 7nm even if it ends up as originally promised and not using relaxed rules to become viable for volume production.
ZolaIII - Thursday, May 24, 2018 - link
When optimized for SIMD NEON extension things changed dramatically. All tho NEON isn't exactly the best SIMD never the less number's speak for them self.https://blog.cloudflare.com/neon-is-the-new-black/
Tho Centriq is a bit pricier, bit overly slower than this but main point is it whose built on comparable lithography to current Intel's 14nm. So you get cheaper hardware, which can be packaged tighter & will consume much less power while being compatible regarding the performance. Triple win situation (initial cost, cost of ownership and scaling) but it still isn't turn key one whit isn't crucial for big vendor server farms anyway.
name99 - Thursday, May 24, 2018 - link
ARM (and this particular chip) aren't trying to solve every problem in the world. They're trying to offer a better (cheaper) solution for a PARTICULAR subset of customers.If you think such customers don't exist, then why do you think Intel has such a wide range of Xeons, including eg all those Xeon Silvers that only turbo up to 3GHz? Or Xeon Gold's that max out at 2.8GHz?
lmcd - Thursday, May 24, 2018 - link
Second page: supports SR-IOV, which is important for KVM and Xen. If you're not aware, Xen and KVM are powerful virtualization solutions that cover the feature set of VMWare quite nicely.HStewart - 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."I different in this - I don't think AnandTech should concentrate on just gaming in focus - this is rather old school - I am not sure about mobile phones in the mess of all this
But comparing ARM cpu's to Intel/AMD is interesting subject. It basically RISC vs CISC discussion - yes RISC can do operations quicker in some cases - but by definition of the architecture they are Reduce in what they do. Fox example it would take RISC a ton of instructions to executed a single AVX style operation.
This article is closest I have seen in comparing ARM vs x86 base machines - but even though I see some holes - it comes close - but having just be Linux based leaves out why people purchase such machine - I think Virtual Machine server is huge - but like everything else on the internet that is just an opinion