The Snapdragon 865 SoC: Beating Expectations

We’ve covered the Snapdragon 865 extensively over the last few months, and more recently did a performance preview of the chip on the Galaxy S20 Ultra:

It’s safe to say that Qualcomm managed to beat our expectations in terms of power efficiency improvements. Which is something we’ll go over in more detail in this piece as well.

At the heart of the Snapdragon 865 we find Arm’s newest Cortex-A77 CPU cores. The new microarchitecture is said to bring a 20-25% IPC improvement over its predecessors, and that’s where the new SoC derives most of its performance improvements from, as the clock frequencies of the cores are identical to that of last year’s Snapdragon 855.


Snapdragon 865 CPU Topology

One aspect where Qualcomm did improve the design is in doubling the shared L3 cache of the CPU cluster, going from 2MB to 4MB. Not only does this further improve the performance of the CPUs by allowing for more data to be cached on-chip, but Qualcomm has explained that one of the primary reasons for this was to also improve power efficiency of the SoC by reducing how often the SoC has to access the DRAM, which is a relatively power-expensive operation.

The chip still has a 3MB system level cache that serves the various IP blocks on the SoC – it’s again meant to not only improve performance but also improve power efficiency as it avoids external memory accesses. The memory subsystem here is smart and detects when to bypass this cache when there’s latency-sensitive workloads, and in general we’ll see some massive memory subsystem improvements on the part of the Snapdragon 865 in a later dedicated section.

All the CPUs being in the same cluster and cache hierarchy means that the core-to-core latencies are relatively uniform, only differing based on their frequencies and lower level cache access latencies. It’s not too much of an exciting metric here, but it’s important context to have as we’ll consider the Exynos 990’s CPU topology in just a bit.

Again, we’ve covered the Snapdragon 865 quite extensively in the above linked articles so I recommend reading them again for other details on other parts of the new chip, such as the new ISP, DSP, and GPU details. However, one aspect that’s very defining for the flagship Qualcomm chipset this year is that the company is separating the modem from the SoC – essentially making the SoC just an application processor for this generation.

The external nature of the X55 modem has a few implications: first of all, there’s an additional component on the motherboard which vendors will have to make space for, which means additional cost. Secondly, there’s the big question of how power efficiency will be affected by the external modem. We’ve seen Apple devices perform excellently over the years while never having an integrated modem, and I feel like the Snapdragon 865 and X55 also fall into this classification, as I haven’t seen any major differences in efficiency due to the external nature of the modem.

Design, Continued: An Ultra Mega Phone The Exynos 990 SoC: Last of Custom CPUs
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  • s.yu - Friday, April 3, 2020 - link

    Not just economy of scale, 5G has higher material cost even if cost per unit is the same, for example you easily need over a dozen antennas in a handset. Massive parallelism is fundamental for 5G. Reply
  • Peskarik - Friday, April 3, 2020 - link

    Swiss watch industry consisted of a large number of small firms that bought in parts from China but marketed at premium price. These will not survive. Rolex/AP/Patek have queues years long, now they also stopped production, there is no excess supply, demand is still there just a bit dormant, especially Asian demand. They will be fine. Omega / Longines will survive due to lower price and high numbers produced. IMHO Reply
  • FunBunny2 - Friday, April 3, 2020 - link

    "Swiss watch industry consisted of a large number of small firms that bought in parts from China but marketed at premium price."

    actually, most are required, by law, to buy Swiss. at least horological parts. of those brands, most are either owned by Swatch or buy movements (more or less complete) from Swatch. a few years ago the Swiss government, after Swatch had bought up ETA and other movement suppliers, allowed Swatch to cease supplying movements to the trade. rather a big stink ensued. last I checked, Swatch had in fact cease supplying.
    Reply
  • damianrobertjones - Thursday, April 23, 2020 - link

    It baffles me that you used a capital S for, 'Swatch', yet didn't place any at the start of your sentences?! What the hell is happening to the English language? Reply
  • Peskarik - Friday, April 3, 2020 - link

    wait for corona to hit economy properly, maybe there will not be so much sales of 1000+ handsets Reply
  • Mgz - Saturday, April 4, 2020 - link

    $1400 is absurd ofc, In Vietnam since we made them so price is more reasonable - but we do not have 5G yet and we have that inferior version Exynos :(
    S20 is 680$
    S20+ is 780$
    S20 Ultra is 930$
    Reply
  • s.yu - Tuesday, April 7, 2020 - link

    Haha, I just looked on Taobao and the price of the SK version is comparable while it's SD this generation.
    I sometimes wonder if the locals in SK could even get that Taobao price off contract.
    Reply
  • RoC_17 - Saturday, April 4, 2020 - link

    Not only is the price tag obsurd, also it's the performance disparities between Snapdragon and Exynos, and weighting that with the price tag is Idiocracy². Why would I buy the Exynos crap for the same price than the Snapdragon parts? I've been with Samsung for nearly 10 years for phones and tablets along, but that's it. That I'm European doesn't mean I am an idiot willing to throw my money out of the window. Reply
  • PallavM - Tuesday, April 7, 2020 - link

    It is for sure, if this is how much the 5G phones are gonna cost I'm happy with my 4G phone Reply
  • StrangerGuy - Wednesday, April 8, 2020 - link

    $1400? Geez, I thought $1100 for the Ultra here in Singapore was already stupid overpriced especially when all S20 variants here are only available in 128GB, and the Note 10+ 256GB is just $590. Reply

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