SPEC - Single Threaded Performance & Power

Moving onto performance of the new CPU cores, something I’ve actually been quite excited about this generation, particularly because this year we hadn’t been able to do a proper in-depth performance preview of the Snapdragon 888 like we usually do on previous years.

Before we go into the results, I wanted to point out some discrepancies between the Exynos 2100 and Snapdragon 888 Galaxy S21 Ultra devices, particularly regarding clock frequencies under load: I’ve noted that the Exynos 2100 CPUs are extremely prone to throttling, in a quite drastic fashion compared my Snapdragon 888 unit. When tracking the average frequencies under SPEC, benchmarking the Exynos 2100 S21 Ultra under my typical peak performance conditions where I place the phone over a 140mm fan to keep it cool, the X1 cores were still throttling quite significantly even though the phone was only luke-warm.

The following are precise mean frequencies for the SPEC workloads, both under my usual fan-cooled conditions, as well as putting the S21 Ultra in my freezer:

Cortex-X1 Average Workload Frequency
  S21 Ultra
(Exynos 2100)
Fan
S21 Ultra
(Exynos 2100)
Freezer
S21 Ultra
(Snapdragon 888)
Fan
400.perlbench 2613 2845 2826
401.bzip2 2690 2904 2841
403.gcc 2688 2905 2839
429.mcf 2744 2912 2841
445.gobmk 2701 2908 2841
456.hmmer 2534 2752 2841
458.sjeng 2684 2912 2841
462.libquantum 2469 2857 2841
464.h264ref 2602 2901 2841
471.omnetpp 2756 2912 2842
473.astar 2667 2909 2841
483.xalancbmk 2668 2909 2841
       
433.milc 2369 2759 2842
444.namd 2603 2912 2841
447.dealII 2721 2889 2841
450.soplex 2573 2883 2841
453.povray 2544 2769 2841
470.lbm 2273 2628 2812
482.sphinx3 2437 2709 2747

The fan-cooled results are quite horrible, with the chip not sustaining the full 2.91GHz for any of the workloads. In this situation, in fact most of the tests barely run at 2912MHz, with most of the time the X1 cores being resident at 2600 or 2496MHz, with many tests going down to 2184MHz for periods of time.

Putting the device in the freezer (with a sock around the bottom part of the phone as to not damage the battery from it getting too cold), resulted in skin temperature hot-spots of around 6 to 10°C. Even under such unrealistic test conditions, the phone wasn’t able to sustain its peak frequency for many workloads, which is quite puzzling and worrying.

This Exynos S21 Ultra unit was quite unlucky in terms of its chip bin as the CPUs received ASV bins of 2, 2, 2 across the little, middle, and big cores. I’ve got another regular Galaxy S21 with another Exynos chip, which had slightly better bins of 4, 4, 3. While this device performed better and was slightly more efficient than the S21 Ultra, it was still significantly worse than the Snapdragon 888 Galaxy S21 Ultra, which had no issues to sustain near its 2841MHz peak frequency for the vast majority of workloads.

The following results are from the freezer-run Exynos S21 Ultra, as we’re attempting to analyse peak performance and the X1 cores themselves as well.

We use SPEC2006 for mobile devices still as it’s still relevant and we have a good understanding of the workloads. The benchmark is deprecated in favour of SPEC2017, which we hope to move to in the coming months. For the Android devices, this data-set is on a new NDK 22 compile as it resolves some performance discrepancies in our past data. We run simple and straightforward -Ofast flags. 

In SPECint2006, we can see the new Cortex-X1 cores in both the Snapdragon 888 and Exynos 2100 perform a notch above the previous generation A77-cores, with particularly some larger jumps in tests such as 403.gcc and 464.h264ref.

The Snapdragon 888 in the majority of tests is able to take the lead, even though for the integer benchmarks the Exynos 2100 was mostly able to retain frequencies near 2.9GHz.

Qualcomm’s lower latency memory subsystem, as well as the advantage of the 1MB L2 cache are quite obvious here as it’s able to overcome, and outpace the clock frequency differences.

It’s to be noted that HiSilicon’s Kirin 9000 is still able to keep up with the new chips in quite a few of the workloads – the Kirin’s 3.13GHz clock frequency as well as an outstanding memory subsystem fall in its favour.

In terms of power and efficiency, it’s very obvious that the Exynos 2100 falls behind the Snapdragon 888. The chip uses more power, and it being slower, means it’s also taking up more energy to complete the tasks.

In SPECfp2006, the Exynos 2100 actually manages to score a few wins against the Snapdragon 888, but again falls behind in others as it has to throttle.

In 433.milc, the new X1 chips are posting gargantuan generational performance bumps, but which comes at a cost of power consumption in excess of 5W – whatever Arm did here this generation, it caught up and surpassed Apple in this one test.

For more extensive performance comparisons to past SoCs, such as the Exynos 990 I’ve updated our historical SPEC mobile data-set in the above large graph.

In the aggregate results scores, there’s a multitude of points we need to analyse.

Starting off with the Exynos 2100 – generationally, the new X1 cores and the Exynos 2100 are able to beat the Exynos 990 and the M5 cores by 27% and 25% in the integer and floating-point results. Samsung had officially stated the new SoC would be 19% faster in single-threaded scenarios – which I immediately throught of as suspect, as the improvements should be larger than that. I’m glad that the marketing was overly conservative and that my initial instinct was correct here. Although the X1 cores don’t use much different power consumption compared to the M5 cores, because of their increased performance, they are more energy efficient, using 23% and 18% less energy than the M5.

Looking at those figures though, they seem quite a bit odd, as they’re not that great as we had expected from the X1 cores, especially since this is also on a process node upgrade. Wouldn’t the cancelled M6 cores still have been competitive here?

The Snapdragon 888 results put things into context – it’s 5.1% and 1.6% faster than the Exynos 2100, however it’s also less power hungry, using 10% less power, resulting in being 14% more energy efficient. That’s not a large difference, but still sizeable given it’s the same CPU IP on the same process node.

Against the Snapdragon 865, the Snapdragon 888’s X1 cores are 23.8% and 29.2% faster. Because the cores are clocked at the same frequency, that’s also the generational IPC improvement that we’ve seen out of the new X1 cores. On the floating-point side, that essentially matches Arm’s 30% projection, however on the integer side it’s a few percentage points short – which is reasonable given that Arm’s figures had been projected with an 8MB L3 cache implementations which we didn’t see this generation.

Energy efficiency of the Snapdragon 888 is only slightly worse than that of the Snapdragon 865+, which means that battery life should still be good this generation.

The Cortex-A78 cores of the Snapdragon 888 are 4.9% and 8.9% faster than the Cortex-A77 middle cores of the Snapdragon 865. The power consumption comparison here isn’t apples-to-apples due to the new cores doubling up on the L2 cache. Arm states the A78 has an +7% IPC improvement and a -4% power reduction versus the A77. The Snapdragon 888’s middle cores however use +24% more power. Excluding the theory that that doubled L2 cache significantly raises power, we’re probably still seeing a notable process node power efficiency difference between Samsung’s 5LPE node and TSMC’s N7P node, with the Samsung node still falling behind.

This power efficiency difference can also be seen in the Cortex-A78 cores of the Exynos 2100. At 2.81GHz, they’re near the 2.84GHz A77 cores of the Snapdragon 865 – both having 512KB L2 caches. The Exynos’ middle cores here actually outperform the previous Snapdragon’s performance cores by 8 and 13%, they however use 35% more power to do so, which is a whole damn lot. In fact, the throttling behaviour on the Exynos wasn’t just limited to the X1 cores, as under normal conditions even these middle A78 cores had to ramp down from their peak frequencies.

This behaviour of these new designs using quite large amounts of power at these higher frequencies, however being seemingly similar power to TSMC’s process nodes at lower frequencies, points out to me that the 5LPE node has lower performance than TSMC’s N7P node. The fact that the Kirin 9000 here is still competitive in terms of performance, but at significant lower power and better energy efficiency, also points out that the N5 node is well superior to Samsung’s offering.

Generally, we can’t do much about the process – especially if TSMC isn’t able to produce enough volume to satisfy both Apple as well as Qualcomm at the same time. Today’s performance and efficiency figures also fell below our projected targets of the X1 cores. Lower frequencies and smaller caches are primary reasons as to why. I find it weird from both Qualcomm as well as SLSI to have employed 4MB L3 caches. SLSI has in the last few years wasted a ton of silicon on their custom cores, so them skimping out even on the L2 cache here on the X1 is a really weird change of philosophy. Qualcomm did a better job, but also not as aggressive as you’d expect from a company which wants to acquire Nuvia in order to strengthen their CPU portfolio.

Memory Subsystem & Latency: Quite Different Mixed-Usage Power & Preliminary Battery Life
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  • watzupken - Monday, February 8, 2021 - link

    Feels like a 20nm all over again. The move to Samsung's fab certainly did not help with the new SD 888 and Samsung's Exynos is able to close the performance gap since they are on the same node. In fact, this review also somewhat confirmed that Nvidia's jump to Samsung's 8nm certainly contributed to the high power consumption and lower clockspeed. Reply
  • s.yu - Monday, February 8, 2021 - link

    That would be saying Samsung's 8nm is worse than TSMC 12nm, it's not that bad, it should be a bit better than TSMC 10nm. Reply
  • Spunjji - Monday, February 8, 2021 - link

    I assumed they meant higher power relative to TSMC 7nm - of course overall power is still a little higher than Turing on TSMC 12nm because of the higher logic density. Reply
  • Otritus - Monday, February 8, 2021 - link

    Samsung's 8nm is based on their 10nm, and can be considered a more refined variant with about a 10% improvement in efficiency. TSMC's 12nm is based on their 16 nm, with about the same efficiency improvements. 10lpp vs 14lpp is about 40% less power. 14lpp was computed to be about 25% less efficient than 16ff+. Which would mean 8lpp has around 20% lower power consumption than 16ff+. Tsmc 10nm should be around 40% less power than 16ff+, so Samsung 8nm is in fact worse than Tsmc 10nm. Reply
  • Silver5urfer - Monday, February 8, 2021 - link

    Samsung 8nm for Nvidia doesn't have much impact in the Desktop PEG scene. Because the GPUs are already heavy on power consumption. Having a TSMC will make it efficient but it won't help with temps / clocks or the performance, always a new node helps with either get perf boost or efficiency.

    Nvidia wanted cheap manufacturing for it's GPUs and more volume. But the latter is busted due to artificially pumping up this BS by Mining craze & corona problem. That's why A100 is on TSMC 7N instead of Samsung, because HPC and other hyperscalers need efficiency.

    In mobile it matters a lot due to the stupid Li Ion garbage tech.
    Reply
  • Otritus - Monday, February 8, 2021 - link

    Efficiency for desktop gpus matters a lot. At best you are limited by temperature and noise, at worst you are also limited by power consumption (primarily oem pcs). If a cooler can dissipate 375 watts at an acceptable noise and temperature threshold, then that's the max power the gpu can ship at(the ceiling is lower if overclocking headroom is considered).

    Switching to tsmc will help temperatures, performance, and clock. Lower power consumption means lower temperatures. The tsmc node can also clock higher which drives performance up. If using tsmc allows the chip to clock n% higher at the same power, ship it with n/2% more frequency, and now performance and oc headroom is higher, and temps and power draw are lower.
    Reply
  • Spunjji - Thursday, February 11, 2021 - link

    Both of the major manufacturer's top-end GPUs are limited by power input and heat dissipation - that's why they rarely perform much better than the next tier down, despite having significantly more execution resources. They do better on a performance-per-watt basis, though, because they're operating at a more sane part of the efficiency curve. Reply
  • geoxile - Monday, February 8, 2021 - link

    Tsmc 12/16nm was roughly on par with Samsung 14nm. Reply
  • melgross - Monday, February 8, 2021 - link

    Yes, when Apple split its SoC production between Samsung and TSMC that one year when they were looking to replace Samsung with TSMC, it was found here, and in other places, that TSMC’ s larger process was 20% more power efficient than Samsung’s smaller process. I think it was the 14 node for Samsung and the 16 for TSMC.

    So nothing seems to have changed. Samsung’s process technology remains inferior to that of TSMC.
    Reply
  • geoxile - Monday, February 8, 2021 - link

    What are you smoking? https://www.tomshardware.com/news/iphone-6s-a9-sam... the Samsung 14nm made A9s had a 10% advantage. Reply

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