Single-Threaded Integer Performance: SPEC CPU2006

Even though SPEC CPU2006 is more HPC and workstation oriented, it contains a good variety of integer workloads. Running SPEC CPU2006 is a good way to evaluate single threaded (or core) performance. The main problem is that the results submitted are "overengineered" and it is very hard to make any fair comparisons.

So we wanted to keep the settings as "real world" as possible. We welcome constructive criticism to reach that goal. So we used:

  • 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 ultimate objective is to measure performance in applications where for some reason – as is frequently the case – a "multi thread unfriendly" task keeps us waiting.

Nobody expect the ThunderX to be a single threaded performance wonder. Cavium clearly stated that they deliberately went for a high core count with pretty simple cores. As a result, single threaded performance was not a priority.

However, Facebook and other hyperscalers have indicated that they definitely prefer to get the single threaded performance of a Xeon D. So any competitor challenging Intel should try to keep up with the Xeon D in single threaded performance and offer a throughput-per-dollar/watt bonus. So it is very interesting to measure what single threaded performance the current ThunderX can offer.

Subtest
SPEC CPU2006
Integer
Application Type Cavium
ThunderX
2 GHz
Xeon D-1557
1.5-2.1
Xeon D-1587
1.8-2.4
Xeon E5-2640 v4
2.4-2.6
Xeon E5-2690 v3
2.6-3.5
Xeon E5-2699 v4
2.2-3.6
Xeon E5-2699 v4
2.2-3.6
(+HT)
400.perlbench Spam filter 8.3 24.7 29 33.4 39 32.2 36.6
401.bzip2 Compression 6.5 15.1 17.2 19.8 24.2 19.2 25.3
403.gcc Compiling 10.8 23.1 27.2 30 37.2 28.9 33.3
429.mcf Vehicle scheduling 10.2 32.6 38.4 40.4 44.8 39 43.9
445.gobmk Game AI 9.2 17.4 20.2 22.7 28.1 22.4 27.7
456.hmmer Protein seq. analyses 4.8 19 21.7 25.1 28 24.2 28.4
458.sjeng Chess 8.8 19.8 22.8 25.6 31.5 24.8 28.3
462.libquantum Quantum sim 5.8 47.9 58.2 60.3 78 59.2 67.3
464.h264ref Video encoding 11.9 32 36.6 41.9 56 40.7 40.7
471.omnetpp Network sim 7 17.3 23 23.6 30.9 23.5 29.9
473.astar Pathfinding 7.9 14.7 17.2 19.8 24.4 18.9 23.6
483.xalancbmk XML processing 8.4 27.8 33.3 36.2 45.1 35.4 41.8

Although some of you have a mathematical mind and are able to easily decipher these kinds of tables, let the rest of us be lazy and translate this into percentages. We make the Xeon D-1581 the baseline. The Xeon D-1557's performance is more or less the single threaded performance some of the important customers such as Facebook like to have.

Subtest
SPEC CPU2006
Integer
Application Type Cavium
ThunderX
2 GHz
Xeon D-1557
1.5-2.1
Xeon D-1581
1.5-2.1
Xeon E5-2640
2.4-2.6
400.perlbench Spam filter 29% 85% 100% 115%
401.bzip2 Compression 38% 88% 100% 115%
403.gcc Compiling 40% 85% 100% 110%
429.mcf Vehicle scheduling 27% 85% 100% 105%
445.gobmk Game AI 46% 86% 100% 112%
456.hmmer Protein seq. analyses 22% 88% 100% 116%
458.sjeng Chess 39% 87% 100% 112%
462.libquantum Quantum sim 10% 82% 100% 104%
464.h264ref Video encoding 33% 87% 100% 114%
471.omnetpp Network sim 30% 75% 100% 103%
473.astar Pathfinding 46% 85% 100% 115%
483.xalancbmk XML processing 25% 83% 100% 109%

First of all, single threaded is somewhat better than we expected when we received the first architectural details (a very simple dual issue core with high latency shared L2). However, this is still a fraction of the Xeon D's single threaded performance, which means that ThunderX doesn't look very impressive to companies which feel that single threaded performance should not be lower than a low end Xeon D. The latter is 2 to 4 times faster. On average, the Xeon D-1581 delivers 3 times faster single threaded performance than the ThunderX, but not 5!

SPEC CPU2006 allows us to characterize the ThunderX core a bit better. We ignore libquantum because it has a very special profile: you can triple the score with specific compiler settings, but those settings reduce performance by 2-30%(!) in some other subtests. Those compiler settings optimize cache utilization by splitting records of an array in separate arrays. Combine this with software loop prefetching and libquantum numbers can indeed double or triple. Since libquantum is hardly relevant for the server world and is known for being a target for all kind of benchmark trickery, we ignore it in our comparison.

Mcf exhibits a large amount of data cache misses and memory controller usage. Mcf is also "horribly low IPC" software, so beefy execution backends do not help. Despite those facts, the ThunderX does not do well in mcf. Mcf does a lot of pointer chasing, so the high latency L2-cache and the high latency DRAM access are slowing things down. That is probably also true for XML processing and the network simulator: those subtests have the highest data cache misses.

The shallow pipeline and relatively powerful gshare branch predictor make the ThunderX a better than expected performer in the chess (sjeng), pathfinding (astar), compiling (gcc) and AI (gobmk). Although the gobmk has a relatively high branch misprediction rate on a gshare branch predictor (the highest of all subtests), the ThunderX core can recover very quickly thanks to its 9 stage pipeline. Notice also that gobmk and gcc have relatively large instruction footprints, which gives the ThunderX and its 78 KB I-cache an advantage.

That is also true for the perl, but that benchmark has a relatively high IPC and needs a beefier execution backend. Indeed, the more compute intensive (and thus high IPC sub tests) perlbench and hmmer perform badly relative to the Intel core. In these benchmarks, the wide architecture of the Intel cores pays off.

Benchmarks Versus Reality Multi-Threaded Integer Performance: SPEC CPU2006
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  • JohanAnandtech - Wednesday, June 15, 2016 - link

    Good suggestion. I have been using an ipmi client to manage several other servers, like the IBM servers. However, such a GUI client is still a bit more userfriendly, ipmi commands can get complicated if you don't use them regularly. The thing is that HP and Intel's BMC GUI are a lot easier to use and more reliable. Reply
  • fanofanand - Wednesday, June 15, 2016 - link

    I think you may have an inaccurate figure of 141 at idle (in the graph) for the Thunder. "makes us suspect that the chip is consuming between 40 and 50W at idle, as measured at the wall" Reply
  • JohanAnandtech - Wednesday, June 15, 2016 - link

    If you look at the Column "peak vs idle", you see 82W. At peak, we assume that a 120W TDP chip will probably need about 130W. 130W - 82W (both measured at the wall) = 50W for the SoC alone at idle measured at the wall, so anywhere between 40-50W in reality. My Calculation is a "guestimate", but it is clear that the Cavium chip needs much more in idle than the Intel chips.(10-15W) . Reply
  • djayjp - Wednesday, June 15, 2016 - link

    Many spelling/grammar issues here. It impacts readability. Please read before posting. Reply
  • djayjp - Wednesday, June 15, 2016 - link

    That is to say in the article. Reply
  • mariush - Wednesday, June 15, 2016 - link

    These guys are already working on ThunderX2 (54 cores, 3 Ghz , 14nm , ARMv8) and they already have functional chips : https://www.youtube.com/watch?v=ei9uVskwPNE Reply
  • Meteor2 - Thursday, June 16, 2016 - link

    It's always jam tomorrow, isn't it? Intel is working on new chips too, you know. Reply
  • beginner99 - Wednesday, June 15, 2016 - link

    It loses very clearly in performance/watt to Xeon-D. In this segment the lower price doesn't matter in that case and the fact that it has a process disadvantage doesn't matter either. What counts is the end result. And I doubt it would cost $800 if made on 14/16nm. I mean why would anyone buying this take the risk? Safer bet to go with Intel also due to more flexible use (single and multi threaded). The latency issue is mentioned but downplayed. Reply
  • blaktron - Wednesday, June 15, 2016 - link

    So downplayed. Anandtech desperately wants ARM servers, but its a solution looking for a problem. Big web front ends running on bare metal are such a small percentage of the server market that developing for it seems stupid. Xeon-D was already in development for SANs, they just repurposed it for docker and nginx. Reply
  • Senti - Wednesday, June 15, 2016 - link

    Very nice article. I especially liked the emphasis on relations of test numbers and real world workloads and what was problematic during the testing.

    It would be great to see the same style desktop CPU review (Zen?) form you instead of mix of reprinted marketing hype with silly benchmark numbers dump that plagues this site for quite some time now.

    Some annoying typos here and there, like "It is clear that the ThunderX is a match for high frequency trading", but nothing really bad.
    Reply

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