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
SPEC CPU2006 Cont: Per-Core Performance w/SMT
Moving beyond single-threaded performance, multi-threaded performance within the confines of a single core is of course also important. The Vulcan CPU architecture was designed from the start to leverage SMT4 to keep its cores occupied and boost their overall throughput, so this is where we'll look next.
| SPEC CPU2006: Single Core w/SMT | ||||||
| Subtest SPEC CPU2006 Integer |
Application Type | Cavium ThunderX 2 GHz gcc 5.2 1 thread |
Cavium ThunderX2 @2.5 GHz gcc 7.2 4 threads |
Xeon 8176 @3.8 GHz gcc 7.2 2 threads |
Thunder X2 vs Xeon 8176 |
Thunder X2 vs ThunderX |
| 400.perlbench | Spam filter | 8.3 | 24.1 | 50.6 | 48% | 290% |
| 401.bzip2 | Compression | 6.5 | 22.9 | 31.9 | 72% | 350% |
| 403.gcc | Compiling | 10.8 | 35 | 38.1 | 92% | 330% |
| 429.mcf | Vehicle scheduling | 10.2 | 52.4 | 50.6 | 104% | 510% |
| 445.gobmk | Game AI | 9.2 | 25.1 | 35.6 | 71% | 270% |
| 456.hmmer | Protein seq. analyses | 4.8 | 26.7 | 41 | 65% | 560% |
| 458.sjeng | Chess | 8.8 | 22.4 | 37.1 | 60% | 250% |
| 462.libquantum | Quantum sim | 5.8 | 83.6 | 83.2 | 100% | 1440% |
| 464.h264ref | Video encoding | 11.9 | 34 | 66.8 | 51% | 290% |
| 471.omnetpp | Network sim | 7.3 | 31.1 | 41.1 | 76% | 440% |
| 473.astar | Pathfinding | 7.9 | 27.2 | 33.8 | 80% | 340% |
| 483.xalancbmk | XML processing | 8.4 | 33.8 | 75.3 | 45% | 400% |
First of all, the ThunderX2 core is a massive improvement over the simple ThunderX core. Even excluding libquantum – that benchmark could easily run 3 times faster on the older ThunderX core after some optimization and compiler improvements – the new ThunderX2 is no less than 3.7 times faster than its older brother. This kind of an IPC advantage makes the original ThunderX's 50% core advantage all but irrelevant.
Looking at the impact of SMT, on average, we see that 4-way SMT improves the ThunderX2's performance by 32%. This ranges from 8% for video encoding to 74% for pathfinding. Intel meanwhile gets a 18% boost from their 2-way SMT, ranging from 4% to 37% in the same respective scenarios.
Overall, a boost of 32% for the ThunderX2 is decent. But it does invite an obvious comparison: how does it fare relative to another SMT4 architecture? Looking at IBM's POWER8, which also supports SMT4, at first glance there seems to be some room for improvement, as the POWER8 sees a 76% boost in the same scenario.
However this isn't entirely an apples-to-apples comparison, as the IBM chip had a much wider back-end: it could issue 10 instructions while the ThunderX2 core is limited to 6 instructions per cycle. The POWER8 core was also much more power hungry: it could fit only 10 of those ultra-wide cores inside a 190W power budget on a 22 nm process. In other words, further increasing the performance gains from using SMT4 would likely require even wider cores, and in turn seriously impact the total number of cores available inside the ThunderX2. Still, it is interesting to put that 32% number into perspective.
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Davenreturns - Wednesday, May 23, 2018 - link
In the spec table for the AMD EPYC 7601 you have max sockets 4 and PCIe 3.0 lanes as 64. I thought the max sockets was 2 and that the total number of PCIe 3.0 lanes was 128 (64 in a dual socket machine).davegraham - Wednesday, May 23, 2018 - link
max sockets is 2 and PCIe lanes is 128 (64 from each 7601 for a combined total of 128; remember, each 7601 has 128 PCIe lanes by themselves. 64 from each are ganged together for IF in a 2P system).davegraham - Wednesday, May 23, 2018 - link
*are not *isDavenreturns - Wednesday, May 23, 2018 - link
But in a single socket motherboard system, the total PCIe lanes available from one EPYC processor is 128 which I think we are both saying is correct.Davenreturns - Wednesday, May 23, 2018 - link
The reason I think these two corrections are important and should be addressed by the author is the way the players in the market are competing. The table should read 128 PCIe lanes and 2 sockets max for EPYC. One only needs to look at AMD's EPYC One socket page to understand why it is important.https://www.amd.com/en/products/epyc-7000-series-1...
The page is filled with marketing trying to convince customers that you are actually getting a two socket server in just one socket. And yes 128 PCIe lanes are available to the customer in these one socket products as part of the reasoning.
The max number of sockets is also important. AMD and probably Cavium are both arguing that 90% of the market only needs 1 or 2 sockets. Intel doesn't agree and provides 4 or more socket configurations.
The one socket argument centers around the I/O and memory channels available in the AMD processor. Even though the table just might have typos, reviewers around the web had a hard time believing that a single chip offered 128 lanes of PCIe connectivity and I found a lot of misinformation. It continues today.
DanNeely - Wednesday, May 23, 2018 - link
AFAIK even for intel 1/2 socket machines are around 90% of their sales. They're just selling enough total server chips in total that catering to the sliver of the market that does want 4/8way configurations is still worth their time.Arnulf - Sunday, May 27, 2018 - link
Profit margins in that market segment are likely to be way higher so it's worth it for Intel as long as there is no competition, forcing prices downwards.Ryan Smith - Wednesday, May 23, 2018 - link
You are correct. Thanks for pointing that out.Davenreturns - Wednesday, May 23, 2018 - link
Thanks so much, Ryan.vanilla_gorilla - Wednesday, May 23, 2018 - link
"This is because the customers who have invested in expensive enterprise software (Oracle, SAP) are less sensitive to cost on the hardware side, so they are much less likely to change to a new hardware platform."I don't really follow the logic here. Just because you spend a lot more money on software doesn't mean you wouldn't try to save money on hardware. You don't only focus on one related expense because it's larger.