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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  • MAGAover9000 - Tuesday, April 7, 2020 - link

    I have the s10+. Fantastic device. Very happy Reply
  • id4andrei - Friday, April 3, 2020 - link

    No need for me to praise this review any longer. Still, I must nitpick. The 3dmark GPU test always has caveats in your reviews. Drop it if you feel it is detected by OEMs or it's a false GPU test like the physics one.

    On web tests. I read on wiki that JetStream is an Apple made test, literally. Wouldn't you say that's a big caveat when testing against ios? Similarly Speedometer is developed by the webkit team at Apple. With Android webview based on Blink, not webkit, wouldn't Android smartphones be at a disadvantage against iphones? I don't see Kraken(Firefox) or Octane(Google) being used.

    Kraken would actually be neutral to both. Other 3rd party tests might be Testdrive(Microsoft) or Basemark.
    Reply
  • Andrei Frumusanu - Friday, April 3, 2020 - link

    I don't think that the fact that the WebKit team made those tests is a valid argument against using them. You can go and read the source JS yourself if you wish, and they're industry accepted benchmarks. Both Kraken and Octane are ancient and outdated and we dropped them just like we dropped SunSpider of the early days. Reply
  • id4andrei - Friday, April 3, 2020 - link

    Thank you for the prompt answer. Reply
  • s.yu - Friday, April 3, 2020 - link

    Thank you Andrei, again the most comprehensive and reliable set of samples anywhere!
    There seems to be considerable sample variation again (last time with Samsung was the main module since S9 with the variable aperture) in the UWA, S20+E and S20UE should have absolutely identical UWA performance but the S20UE seems to have far worse sagittal resolution than the S20+E, and Samsung's processing isn't that good in the first place, considering the 12MP 1.4μm could produce incredibly sharp pictures as that been the specs of the Pixels' main module for generations.
    I don't regret their switch to f/1.8 because the old module that went up to f/1.5 wasn't sharp wide open, especially in the corners, but a further two stops' variation to f/3.3 could be useful for more DoF in closeups provided inserting that physical aperture into the tiny module doesn't compromise the optical design otherwise.
    This time around the E seems to generally outperform the S, except in color as E doesn't seem to have proper color fidelity...almost as if chroma NR is set too high even in broad daylight, and the "hybridization" of the digital zoom, in which the E clearly uses a smaller portion from the periscope's readout than the S in the resulting merge. Speaking of the zoom, S20+ still performs slightly worse at 2x(16MP readout) than S10's native 12MP, though the difference is small and could be down to lens variation. Considering S10U's Z height, they could've easily fixed the S20U like Xiaomi, going 1/2.3" f/2 12MP with the 2x. Xiaomi used it despite a 4-1 bin, all the more reason to use it with a 9-1 bin. S20U's corner performance at 3x would also be much improved.
    Regarding the comparison with the Fuji though, I suspect your unit has trouble focusing to infinity correctly, because the train and forest samples show clear superiority of the Fuji's zoom. I especially recognize that kind of slight haziness as being very responsive to dehaze and low radius sharpening in LR and would result in far more detail with extraction in post. Also, with an ILC, there's always stopping down a little for more sharpness and more DoF.
    Regarding the full res modes, it's not worth storing 108MP of data with the CFA asking for a 9-1 bin, of course the 64MP would be better, without the RAW it's hard to say for sure, but the 64MP seems to be quad bayer.
    Reply
  • s.yu - Friday, April 3, 2020 - link

    I don't agree with your remark about the night comparison with Mate30P though, the UWA is not "UW" so it has better image quality, that's true, and the night mode of the Mate30P is far superior, that's also true, but not auto mode, nor any aspect of the telephoto as it's clearly using a crop of the main for 3x. Samsung does attempt to use the 4x for telephoto and although there's a significant issue of chroma noise, it's far sharper than Mate30P's crop, with at least twice 3 times the effective resolution in night mode. With S20U you could also crop out a single shot 3-4x of similar brightness to the Mate30P crop, but it's just a crop.
    As for the potential of P40P surpassing S20U, that model operates on a 9.4MP crop by default, interpolated to 12.5MP which clearly has consequences. In daylight it's often a regression compared to P30P (much less match Mate30P), and in night shots using the current firmware it has severe color issues of rendering large portions of the scene as a crimson red, so it's hard to say at this point too.
    Reply
  • s.yu - Friday, April 3, 2020 - link

    Oh, there's exception of the Mate30P auto mode in the last sample, but the night mode isn't constantly superior either. Reply
  • RealBeast - Friday, April 3, 2020 - link

    I've been looking forward to getting one of these, not sure which yet. The fly in the ointment now is that I won't see my Mom (who gets my old S9+) until the Fall due to the whole COVID problem, not to mention less income. That will weigh heavily on sales of what is otherwise an amazing looking phone for me. Reply
  • 29a - Friday, April 3, 2020 - link

    How large are the picture file sizes created by this thing? Reply
  • BedfordTim - Sunday, April 5, 2020 - link

    The same size as any other 12MP camera. They will depend on content, hdr, motion and compression options but I would expect about 36MB for a raw image and 8MB for a high quality jpeg. Reply

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