Comparing Skylake-S and Skylake-X/SP Performance Clock-for-Clock

If you’ve read through the full review up to this point (and kudos), there should be three things that stick in the back of your mind about the new Skylake-SP cores: Cache, Mesh and AVX512. These are the three main features that separate the consumer grade Skylake-S core from this new core, and all three can have an impact in clock-for-clock performance. Even though the Skylake-S and the Skylake-SP are not competing in the same markets, it is still poignant to gather how much the changes affect the regular benchmark suite.

For this test, we took the Skylake-S based Core i5-6600 and the Skylake-SP based Core i9-7900X and ran them both with only 4 cores, no hyperthreading, and 3 GHz on all cores with no Turbo active. Both CPUs were run in high performance modes in the OS to restrict any time-to-idle, so it is worth noting here that we are not measuring power. This is just raw throughput.

Both of these cores support different DRAM frequencies, however: the i5-6600 lists DDR4-2133 as its maximum supported frequency, whereas the i9-7900X will run at DDR4-2400 at 2DPC. I queried a few colleagues as to what I should do here – technically the memory support is an extended element of the microarchitecture, and the caches/uncore/untile will be running at different frequencies, so how much of the system support should be chipped away for parity. The general consensus was to test with the supported frequencies, given this is how the parts ship.

For this analysis, each test was broken down in two ways: what sort of benchmark (single thread, multi-thread, mixed) and what category of benchmark (web, office, encode).

 

For the single threaded tests, results were generally positive. Kraken enjoyed the L2, and Dolphin emulation had a good gain as well. The legacy tests did not fair that great: 3DPM v1 has false sharing, which is likely taking a hit due to the increased L2 latency.

On the multithreaded tests, the big winner here was Corona. Corona is a high-performance renderer for Autodesk 3ds Max, showing that the larger L2 does a good job with its code base. The step back was in Handbrake – our testing does not implement any AVX512 code, but the L3 victim cache might be at play here over the L3 inclusive cache in SKL-S.

The mixed results are surprising: these tests vary with ST and MT parts to their computation, some being cache sensitive as well. The big outlier here is the compile test, indicating that the Skylake-SP might not be (clock for clock) a great compilation core. This is a result we can trace back to the L3 again, being a smaller non-inclusive cache. In our results database, we can see similar results when comparing a Ryzen 7 1700X, an 8-core 95W CPU with 16MB of L3 victim cache, is easily beaten by a Core i7-7700T, with 4 cores at 35W but has 8MB of inclusive L3 cache.

If we treat each of these tests with equal weighting, the overall result will offer a +0.5% gain to the new Skylake-SP core, which is with the margin of error. Nothing too much to be concerned about for most users (except perhaps people who compile all day), although again, these two cores are not in chips that directly compete. The 10-core SKL-SP chip still does the business on compiling:

Office: Chromium Compile (v56)

If all these changes (minus AVX512) offer a +0.5% gain over the standard Skylake-S core, then one question worth asking is what was the point? The answer is usually simple, and I suspect involves scaling (moving to chips with more cores), but also customer related. Intel’s big money comes from the enterprise, and no doubt some of Intel’s internal metrics (as well as customer requests) point to a sizeable chunk of enterprise compute being L2 size limited. I’ll be looking forward to Johan’s review on the enterprise side when the time comes.

Benchmarking Performance: CPU Legacy Tests Intel Skylake-X Core i9-7900X, i7-7820X and i7-7800X Conclusion
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  • slickr - Tuesday, July 4, 2017 - link

    I've been a long time user here and I can SAFELY say you got paid by Intel. How much did they pay you for this ridiculous review? Reply
  • nevcairiel - Monday, June 19, 2017 - link

    The Ryzen 7 launch review didn't have gaming benchmarks either. Reply
  • ddriver - Monday, June 19, 2017 - link

    That's true, my bad, I didn't remember AT's review in particular, but I remember in most reviews gaming was like 3/4 of the review... Reply
  • Spunjji - Tuesday, June 20, 2017 - link

    My thoughts exactly. Not bagging on AT specifically here, just review sites in general. A lot of them are giving out TBD on gaming performance with mentions of it being OK at 4K, whereas with Ryzen it was all "but it games badly at 1080p which people spending $500 on a processor will totally be aiming at". Reply
  • bongey - Wednesday, August 2, 2017 - link

    They said it in their conclusion "Gaming Performance, particularly towards 240 Hz gaming, is being questioned,"
    "workstation cpu"
    Reply
  • ash9 - Monday, June 19, 2017 - link

    Totally agree,
    I find it disingenuous by this site and many others that there's an INTENTIONAL over look to the fact that the 7900X runs 70W higher (PC Perspective) than the 6950X at load- any blind man could see Intel boosted the clocks on the 7900X for cosmetic benchmark wins and to make this lineup today look relevant. Take the 7900X out of the benches and the lineup today looks anemic. This is the BS that should not go unnoticed
    Reply
  • Alexvrb - Monday, June 19, 2017 - link

    Reminds me a bit of the pre-Conroe era. Maybe they should have revived the Extreme Edition name... Reply
  • sweetca - Tuesday, June 20, 2017 - link

    Some people actually read the reviews here because they are gathering information for an imminent decision.

    Not everyone wants to wait 3 weeks (maybe delays?), and then to play it safe wait another 3 weeks for the next thing, etc.

    I don't post often, but I was surprised how quickly the writer's integrity and honesty were attacked, considering they were making a subjective evaluation; "safe." I guess this is common now.
    Reply
  • Timoo - Saturday, July 1, 2017 - link

    To be honest: calling the i9 7900X a "safe bet" is not a scientific decision. The platform is far from perfect and the CPU runs hot when OC'd. It has been introduced 2 months in advance of the official release date, to beat TR. To me these 3 facts don't make it a "safe bet", more like a "daring endeavor to save Intel's face".

    So yes, I do understand the attacks, apart from the FanBoy's FlameBaits...
    Reply
  • someonesomewherelse - Saturday, October 14, 2017 - link

    It's pretty safe if you can't actually buy it. Just don't buy it and later get a TR :) Reply

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