CPU Performance & Efficiency: SPEC2006

We’re moving on to SPEC2006, analysing the new single-threaded performance of the new Cortex-A77 cores. As the new CPU is running at the same clock as the A76-derived design of the Snapdragon 855, any improvements we’ll be seeing today are likely due to the IPC improvements of the core, the doubled L3 cache, as well as the enhancements to the memory controllers and memory subsystem of the chip.

Disclaimer About Power Figures Today:

The power figures presented today were captured using the same methodology we generally use on commercial devices, however this year we’ve noted a large discrepancy between figures reported by the QRD865’s fuel-gauge and the actual power consumption of the device. Generally, we’ve noted that there’s a discrepancy factor of roughly 3x. We’ve reached out to Qualcomm and they confirmed in a very quick testing that there’s a discrepancy of >2.5x. Furthermore, the QRD865 phones this year again suffered from excessive idle power figures of >1.3W.

I’ve attempted to compensate the data as best I could, however the figures published today are merely preliminary and of lower confidence than usual. For what it’s worth, last year, the QRD855 data was within 5% of the commercial phones’ measurements. We’ll be naturally re-testing everything once we get our hands on final commercial devices.

In the SPECint2006 suite, we’re seeing some noticeable performance improvements across the board, with some benchmarks posting some larger than expected increases. The biggest improvements are seen in the memory intensive workloads. 429.mcf is DRAM latency bound and sees a massive improvement of up to 46% compared to the Snapdragon 855.

What’s interesting to see is that some execution bound benchmarks such as 456.hmmer seeing a 28% upgrade. The A77 has an added 4th ALU which represents a 33% throughput increase in simple integer operations, which I don’t doubt is a major reason for the improvements seen here.

The improvements aren’t across the board, with 400.perlbench in particular seeing even a slight degradation for some reason. 403.gcc also saw a smaller 12% increase – it’s likely these benchmarks are bound by other aspects of the microarchitecture.

The power consumption and energy efficiency, if the numbers are correct, roughly match our expectations of the microarchitecture. Power has gone up with performance, but because of the higher performance and smaller runtime of the workloads, energy usage has remained roughly flat. Actually in several tests it’s actually improved in terms of efficiency when compared to the Snapdragon 855, but we’ll have to wait on commercial devices in order to make some definitive conclusions here.

In the SPECfp2006 suite, we’re seeing also seeing some very varied improvements. The biggest change happened to 470.lbm which has a very big hot loop and is memory bandwidth hungry. I think the A77’s new MOP-cache here would help a lot in regards to the instruction throughput, and the improved memory subsystem makes the massive 65% performance jump possible.

Arm actually had advertised IPC improvements of ~25% and ~35% for the int and FP suite of SPEC2006. On the int side, we’re indeed hitting 25% on the Snapdragon 865, compared to the S855, however on the FP side we’re a bit short as the increase falls in at around 29%. The performance increases here strongly depend on the SoC and particular on the memory subsystem, compared to the Kirin 990’s A76 implementation the increases here are only 20% and 24%, but HiSilicon’s chip also has a stronger memory subsystem which allows it to gain quite more performance over the A76’s in the S855.

The overall results for SPEC2006 are very good for the Snapdragon 865. Performance is exactly where Qualcomm advertised it would land at, and we’re seeing a 25% increase in SPECint2006 and a 29% in SPECfp2006. On the integer side, the A77 still trails Apple’s Monsoon cores in the A11, but the new Arm design now has been able to trounce it in the FP suite. We’re still a bit far away from the microarchitectures catching up to Apple’s latest designs, but if Arm keeps up this 25-30% yearly improvement rate, we should be getting there in a few more iterations.

The power and energy efficiency figures, again, taken with a grain of salt, are also very much in line with expectations. Power has slightly increased with performance this generation, however due to the performance increase, energy efficiency has remained relatively flat, or has even seen a slight improvement.

Introduction & Specifications System Performance
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  • rpg1966 - Monday, December 16, 2019 - link

    How is Apple so far ahead in some/many respects, given that Arm is dedicated to designing these microarchitectures? Reply
  • eastcoast_pete - Monday, December 16, 2019 - link

    In addition to spending $$$ on R&D, Apple can optimize (tailor, really) its SoCs 100% to its OS and vice versa. Also, not sure if anybody has figures just how much the (internal) costs of Apple's SoCs are compared to what Samsung, Xiaomi etc. pay QC for their flagship SoCs. Would be interesting to know how much this boils down to costs. Reply
  • jospoortvliet - Monday, December 16, 2019 - link

    I think cody I'd the big factor. Qualcomm and arm keep chips small for cost reasons. Apple throws transistors at the problem and cares little... Reply
  • s.yu - Monday, December 16, 2019 - link

    I like the approach of throwing transistors :) Reply
  • generalako - Monday, December 16, 2019 - link

    Can we stop with these excuses? What cost reasons? Whose stopping them from making two architectures then, letting OEMs decide which to use -- if Apple does it, why not them? Samsung aiming at large cores with their failed M4 clearly points towards a desire/intention to have larger cores that are more performant. Let's not make the assumption that there's no need here--there clearly is.

    Furthermore, where is the excuse in ARM still being on the A55 for the third straight year? Or Qualcomm being on their GPU architecture for 3 straight years, with so incremental GPU improvements the past two years that they not only let Apple both match and vastly surpass them, but are even getting matched by Mali?

    There's simply no excuse for the laziness going on. ARM's architecture is actually impressive, with still big year-on-year IPC gains (whereas Apple has actually stagnated here the past two years). But abandoning any work on efficiency cores is inexcusable. As is the fact that none of the OEMs has done anything to deal with this problem.
    Reply
  • Retycint - Monday, December 16, 2019 - link

    Probably because ARM designs for general use - mobiles, tablets, TVs, cars etc, whereas Apple designs specifically for their devices. So naturally Apple is able to devote more resources and time to optimize for their platform, and also design cores/chips specific to their use (phone or tablet).

    But then again I'm an outsider, so the reality could be entirely different
    Reply
  • generalako - Monday, December 16, 2019 - link

    TIL using the same A55 architecture is "for general use" /s

    If ARM had actually done their job and released efficiency cores more often, like Apple does every year, we'd have far more performant and efficient smartphones today across the spectrum. Flagship phones would benefit in idle use (including standby), and also in assigning far more resource-mild works to these cores than they do today.

    But mid-range and low-end phones would benefit a huge amount here, with efficiency cores performing close to performance cores (often 1-2 older gen clocked substantially lower). That would also be cheaper, as it would make cluster of 2 performance cores not as necessary--fitting right in with your logic of making cheap designs for general use.
    Reply
  • quadrivial - Monday, December 16, 2019 - link

    There's a few reasons.

    Apple seems to have started before arm did. They launched their design just 2 years or so after the announcement of a64 while arm needed the usual 4-5 years for a new design. I don't believe apples designers are that much better than normal (I think they handed them the ISA and threatened to buy out MIPS if they didn't). Arm has never recovered that lead time.

    That said, PA Semi had a bunch of great designers who has already done a lot of work with low power designs (mostly POWER designs if I recall correctly).

    Another factor is a32 support. It's a much more complex design and doesn't do performance, power consumption, or die area any favors. Apple has ecosystem control, so they just dropped the complex parts and just did a64. This also drastically reduces time to design any particular part of the core and less time to verify everything meaning more time optimizing vs teams trying to do both at once.

    Finally, Apple has a vested interest in getting faster as fast as possible. Arm and the mobile market want gradual performance updates to encourage upgrades. Even if they could design an iPhone killer today, I don't think they would. There's already enough trouble with people believing their phones are fast enough as is.

    Apple isn't designing these chips for phones though. They make them for their pro tablets. The performance push is even more important for laptops though. The current chip is close to x86 in mobile performance. Their upcoming 5nm designs should be right at x86 performance for consumer applications while using a fraction of the power. They're already including a harvested mobile chip in every laptop for their T2. Getting rid of Intel on their MacBook air would do two things. It would improve profits per unit by a hundred dollars or so (that's almost 10% of low end models). It also threatens Intel to get them better deals on higher end models.

    We may see arm move in a similar direction, but they can't get away with mandating their users and developers change architectures. Their early attempts with things like the surface or server chips (a57 was mostly for servers with a72 being the more mobile-focused design) fell flat. As a result, they seem to be taking a conservative approach that eliminates risk to their core market.

    The success or failure of the 8cx will probably be extremely impactful on future arm designs. If it achieves success, then focusing on shipping powerful, 64-bit only chip designs seems much more likely. I like my Pixelbook, but I'd be willing to try an 8cx if the price and features were right (that includes support for Linux containers).
    Reply
  • Raqia - Monday, December 16, 2019 - link

    Nice post! You're right, it really does seem like Apple's own implementations defined the ARM v8.x spec given how soon after ARM's release their chips dropped. ARM is also crimped by the need to address server markets so their chips have a more complex cache and uncore hierarchies than Apple's and generally smaller caches with lower single threaded performance. Their customers' area budgets are also more limited compared to Apple who doesn't generally integrate a modem into their SoC designs. Reply
  • aliasfox - Monday, December 16, 2019 - link

    I would also add that Qualcomm only makes a dozen or so dollars per chip, whereas Apple makes hundreds of dollars per newest generation iPhone and iPad Pro. Qualcomm's business model just puts them at a disadvantage in this case - they have to make a chip that's not only competitive in performance, but at a low enough cost that a) they can make money selling it, and b) handset vendors can make money using it. Apple doesn't really have to worry about that because for all intents and purposes, their chip division is a part of their mobile division.

    I wonder if it's in the cards for Apple to ever include both an Intel processor as well as a full fledged mobile chip in the future, working in the same way as integrated/discrete graphics - the system would primarily run on the A13x, with the Intel chip firing up for Intel-binary apps as needed.
    Reply

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