AMD Rome Second Generation EPYC Review: 2x 64-core Benchmarked

Single-Thread SPEC CPU2006 Estimates

While it may have been superceded by SPEC2017, we have built up a lot of experience with SPEC CPU2006. Considering the trouble we experience with our datacenter infrastructure, it was our best first round option for raw performance analysis.   

Single threaded performance continues to be very important, especially in maintainance and setup situations. These examples may include running a massive bash script, trying out a very complex SQL query, or configuring new software - there are lots of times where a user simply does not use all the cores. 

Even though SPEC CPU2006 is more HPC and workstation oriented, it contains a good variety of integer workloads. It is our conviction that we should try to mimic how performance critical software is compiled instead of trying to achieve the highest scores. To that end, we:

• use 64 bit gcc : by far the most used compiler on linux for integer workloads, good all round compiler that does not try to "break" benchmarks (libquantum...) or favor a certain architecture
• use gcc version 7.4 and 8.3: standard compiler with Ubuntu 18.04 LTS and 19.04. 
• use -Ofast -fno-strict-aliasing optimization: a good balance between performance and keeping things simple
• added "-std=gnu89" to the portability settings to resolve the issue that some tests will not compile 

The ultimate objective is to measure performance in non-aggressively optimized"applications where for some reason – as is frequently the case – a multi-thread unfriendly task keeps us waiting. The disadvantage is there are still quite a few situations where gcc generates suboptimal code, which causes quite a stir when compared to ICC or AOCC results that are optimized to look for specific optimizations in SPEC code. 

First the single threaded results. It is important to note that thanks to turbo technology, all CPUs will run at higher clock speeds than their base clock speed. 

• The Xeon E5-2699 v4  ("Broadwell") is capable of boosting up to 3.6 GHz. Note: these are old results compiled w GCC 5.4
• The Xeon 8176 ("Skylake-SP") is capable of boosting up to 3.8 GHz. 
• The EPYC 7601 ("Naples") is capable of boosting up to 3.2 GHz. 
• The EPYC 7742 ("Rome") boosts to 3.4 GHz. Results are compiled with GCC 7.4 and 8.3

Unfortunately we could not test the Intel Xeon 8280 in time for this data. However, the Intel Xeon 8280 will deliver very similar results, the main difference being that it runs a 5% higher clock (4 GHz vs 3.8 GHz). So we basically expect the results to be 3-5% higher than the Xeon 8176. 

As per SPEC licensing rules, as these results have not been officially submitted to the SPEC database, we have to declare them as Estimated Results.

A SPEC CPU analysis is always complicated, being a mix of what kind of code the compiler produces and CPU architecture.

First of all, the most interesting datapoint was the fact that the code generated by gcc 8 seems to have improved vastly for the EPYC processors. We repeated the single threaded test three times, and the rate numbers show the same thing: it is very consistent. 

hmmer is one of the more branch intensive benchmarks, and the other two workloads where the impact of branch prediction is higher (somewhat higher percentage of branch misses) - gobmk, sjeng - perform consistingly better on the second generation EPYC with it's new TAGE predictor. 

Why the low IPC omnetpp ("network sim") does not show any improvement is a mystery to us, we expected that the larger L3 cache would help. However this is a test that loves very large caches, as a result the Intel Xeons have the advantage (38.5 - 55 MB L3). 

The video encoding benchmark "h264ref" also relies somewhat on the L3 cache, but that benchmark relies much more on DRAM bandwidth. The fact that the EPYC 7002 has higher DRAM bandwidth is clearly visible. 

The pointer chasing benchmarks – XML procesing and Path finding – performed less than optimal on the previous EPYC generation (compared to the Xeons), but show very significant improvements on EPYC 7002.