The following chart shows the Phoronix test suite coremark value when running from 1 to 16 cores.

Cores	Coremark	Scaling	Retiring	Frontend	Backend	Speculation	SMT-contention
1	43881	100%	43.9%	12.4%	43.0%	0.7%	0.0%
2	85758	98%	43.9%	12.4%	43.1%	0.7%	0.0%
3	128841	98%	43.6%	13.0%	42.7%	0.7%	0.0%
4	171061	97%	43.9%	12.3%	43.1%	0.7%	0.0%
5	210368	96%	43.9%	12.3%	43.1%	0.7%	0.0%
6	251705	96%	43.2%	12.9%	43.2%	0.7%	0.0%
7	281369	92%	43.3%	12.2%	43.7%	0.7%	0.0%
8	319098	91%	42.7%	12.8%	43.8%	0.7%	0.0%
9	334602	85%	40.2%	15.9%	36.3%	0.6%	7.1%
10	347246	79%	38.4%	17.8%	30.2%	0.5%	13.1%
11	359402	74%	36.9%	19.6%	25.3%	0.5%	17.8%
12	363288	69%	35.5%	21.1%	21.6%	0.4%	21.3%
13	362144	63%	34.4%	22.4%	18.5%	0.4%	24.3%
14	377767	61%	33.1%	24.4%	15.2%	0.4%	26.9%
15	397145	60%	32.2%	25.3%	12.0%	0.3%	30.2%
16	418462	60%	31.1%	26.0%	9.5%	0.3%	33.1%

Graphically it looks as follows

The question is what causes the inflection points on the graph? The scaling from 1-8 cores decreases only slightly and my guess is the inflection point after this happens because of SMT contention. What is interesting is the second inflection point where for the first few additional SMT cores we decline but then settle in after that to become asymptotic to ~60% scaling.

Looking at the topdown performance counter profiles gives two general trends

• As hyper-threaded cores are used, the amount of SMT contention goes up. This is somewhat expected for this workload with moderately high retirement rate. One limiter is is that the core is busy with the other thread.
• The workload shifts from being more backend bound (43% down to 9.5%) to being more frontend bound (12.4% up to 26.0%). Assume a few effects here. Waiting on memory goes down from 34.4% to 6.9%, presumably because these multiple threads are making better use of caches. CPU also goes down but not as much. On the frontend side both latency stalls and bandwidth stalls become more important.

This test is useful to compare with other workloads and also other processors.