Favored Core

For Broadwell-E, the last generation of Intel’s HEDT platform, we were introduced to the term ‘Favored Core’, which was given the title of Turbo Boost Max 3.0. The idea here is that each piece of silicon that comes off of the production line is different (which is then binned to match to a SKU), but within a piece of silicon the cores themselves will have different frequency and voltage characteristics. The one core that is determined to be the best is called the ‘Favored Core’, and when Intel’s Windows 10 driver and software were in place, single threaded workloads were moved to this favored core to run faster.

In theory, it was good – a step above the generic Turbo Boost 2.0 and offered an extra 100-200 MHz for single threaded applications. In practice, it was flawed: motherboard manufacturers didn’t support it, or they had it disabled in the BIOS by default. Users had to install the drivers and software as well – without the combination of all of these at work, the favored core feature didn’t work at all.

Intel is changing the feature for Skylake-X, with an upgrade and for ease-of-use. The driver and software are now part of Windows updates, so users will get them automatically (if you don’t want it, you have to disable it manually). With Skylake-X, instead of one core being the favored core, there are two cores in this family. As a result, two apps can be run at the higher frequency, or one app that needs two cores can participate. 

Speed Shift

In Skylake-S, the processor has been designed in a way that with the right commands, the OS can hand control of the frequency and voltage back to the processor. Intel called this technology 'Speed Shift'. We’ve discussed Speed Shift before in the Skylake architecture analysis, and it now comes to Skylake-X. One of the requirements for Speed Shift is that it requires operating system support to be able to hand over control of the processor performance to the CPU, and Intel has had to work with Microsoft in order to get this functionality enabled in Windows 10.

Compared to Speed Step / P-state transitions, Intel's new Speed Shift terminology changes the game by having the operating system relinquish some or all control of the P-States, and handing that control off to the processor. This has a couple of noticeable benefits. First, it is much faster for the processor to control the ramp up and down in frequency, compared to OS control. Second, the processor has much finer control over its states, allowing it to choose the most optimum performance level for a given task, and therefore using less energy as a result. Specific jumps in frequency are reduced to around 1ms with Speed Shift's CPU control from 20-30 ms on OS control, and going from an efficient power state to maximum performance can be done in around 35 ms, compared to around 100 ms with the legacy implementation. As seen in the images below, neither technology can jump from low to high instantly, because to maintain data coherency through frequency/voltage changes there is an element of gradient as data is realigned.

The ability to quickly ramp up performance is done to increase overall responsiveness of the system, rather than linger at lower frequencies waiting for OS to pass commands through a translation layer. Speed Shift cannot increase absolute maximum performance, but on short workloads that require a brief burst of performance, it can make a big difference in how quickly that task gets done. Ultimately, much of what we do falls more into this category, such as web browsing or office work. As an example, web browsing is all about getting the page loaded quickly, and then getting the processor back down to idle.

Again, Speed Shift is something that needs to be enabled on all levels - CPU, OS, driver, and motherboard BIOS. It has come to light that some motherboard manufacturers are disabling Speed Shift on desktops by default, negating the feature. In the BIOS is it labeled either as Speed Shift or Hardware P-States, and sometimes even has non-descript options. Unfortunately, a combination of this and other issues has led to a small problem on X299 motherboards.

X299 Motherboards

When we started testing for this review, the main instructions we were given was that when changing between Skylake-X and Kaby Lake-X processors, be sure to remove AC power and hold the reset BIOS button for 30 seconds. This comes down to an issue with supporting both sets of CPUs at once: Skylake-X features some form of integrated voltage regulator (somewhat like the FIVR on Broadwell), whereas Kaby Lake-X is more motherboard controlled. As a result, some of the voltages going in to the CPU, if configured incorrectly, can cause damage. This is where I say I broke a CPU: our Kaby Lake-X Core i7 died on the test bed. We are told that in the future there should be a way to switch between the two without having this issue, but there are some other issues as well.

After speaking with a number of journalists in my close circle, it was clear that some of the GPU testing was not reflective of where the processors sat in the product stack. Some results were 25-50% worse than we expected for Skylake-X (Kaby Lake-X seemingly unaffected), scoring disastrously low frame rates. This was worrying.

Speaking with the motherboard manufacturers, it's coming down to a few issues: managing the mesh frequency (and if the mesh frequency has a turbo), controlling turbo modes, and controlling features like Speed Shift. 'Controlling' in this case can mean boosting voltages to support it better, overriding the default behavior for 'performance' which works on some tests but not others, or disabling the feature completely.

We were still getting new BIOSes two days before launch, right when I need to fly half-way across the world to cover other events. Even retesting the latest BIOS we had for the boards we had, there still seems to be an underlying issue with either the games or the power management involved. This isn't necessarily a code optimization issue for the games themselves: the base microarchitecture on the CPU is still the same with a slight cache adjustment, so if a Skylake-X starts performing below an old Sandy Bridge Core i3, it's not on the game.

We're still waiting to hear for BIOS updates, or reasons why this is the case. Some games are affected a lot, others not at all. Any game we are testing which ends up being GPU limited is unaffected, showing that this is a CPU issue.

Analyzing The Silicon: Die Size Estimates and Arrangements Power Consumption, Test Bed and Setup
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  • jjj - Monday, June 19, 2017 - link

    The 10 cores die is clearly 320+mm2 not 308mm2. The 308mm figure rounds down the mm based on those GamerNexus pics. From there, you slightly underestimate the size of other 2 die. Reply
  • Sarah Terra - Monday, June 19, 2017 - link

    Fair point but what I take from this review is that you are going to be spending pretty much double the cost or higher of ryzen for a proc that will have a 30% larger power envelope if you want higher performance. Intel is scrambling here, well done AMD. Reply
  • jjj - Monday, June 19, 2017 - link

    With 8 cores and up, thermal is a big issue when you OC Skylake X.. Power also to some extent.
    The 6 cores looks interesting vs the 7700k but not so much vs anything else. CPU+mobo gets you north of 600$ and that's a lot. If it had all the PCIe lanes enabled, there would be that but ,while plenty will buy it, it makes no sense to. And ofc there should be a Coffee Lake 6 cores soon , we'll see how it is priced- in consumer 6 cores with 2 mem chans is fine.
    More than 6 cores are priced way too high and , if you need many cores, you buy for MT not ST so ST clocks are less relevant.

    Intel moving in the same direction as AMD on the cache size front is interesting- larger L2 and smaller L3. Now they have "huge cache and memory latency issues"" just like Ryzen lol.
    W/e, Intel's pricing is still far too high and this platform remains of minimal relevance.
    Reply
  • ddriver - Monday, June 19, 2017 - link

    Funny thou, when Ryzen under-performed in games that was no reason to not publish gaming benches, in fact being the platform's main weakness there was actually emphasis put on that... but when it comes to intel we gotta have special treatment... Let's hear it for objectivity!

    Granted the 7800X finally brings something of relatively decent value, but still no good reason to justify the purchase unless one insists on an intel product, for the brand, for thunderbolt or hypetane support.

    "To play it safe, invest in the Core i9-7900X today."

    Really? With Threadripper incoming in a matter of weeks? For less than 1000$ you will get 16 zen cores. It will definitely beat the 7900X by a decent margin in terms of performance, plus the massive I/O capabilities and also ECC support, which I'd say is vital. That just doesn't sound like a honest recommendation. Not surprising in the least.
    Reply
  • ddriver - Monday, June 19, 2017 - link

    Also, on top of that we have launch prices for Ryzen rather than current prices. Looks like a rather open attempt to diminish AMD's platform value. Reply
  • Ian Cutress - Tuesday, June 20, 2017 - link

    We've always posted manufacturer MSRPs in our CPU charts. There has been no official price drop from AMD; if you're seeing lower, it's being run from the distributor level.

    On the TR issue, we basically haven't tested it and don't know the price. Lots of variables in the air, which is why the words are /if you want to play it safe/. Safe being the key word there.
    Reply
  • ddriver - Tuesday, June 20, 2017 - link

    Dunno Ian, in my book this sounds more like hasty than safe. The safe thing would be to wait out. Even without the incipient TR launch, early adoption is rather unsafe on its own. As it is, it sounds more like an attempt to dupe people into spending their money on intel in the eve of the launch of a superior value and performance product from a direct (and sole) competitor.

    It is true that nothing is still officially known about TR, but based on the ryzen marketing strategy and performance we can make safe and accurate speculations. I expect to see the top TR chip launched at 999$ offering at the very least 30% of performance advantage over the 7900X in a similar or slightly higher thermal budget, of course in workloads that can scale nicely up with the core count.

    Comparing the 7900X to the 1800X, we have ~35% performance advantage for 205% the price and 150% the power usage. Based on that, it is a safe bet that TR is going to shine.
    Reply
  • fanofanand - Monday, June 26, 2017 - link

    Ian is a scientist, the less guessing the better. Give him an opportunity to review TR before giving suggestions. Doesn't that seem fair? Reply
  • t.s - Tuesday, June 20, 2017 - link

    Play it safe? Really?? Please. As if everyone in this world's stupid. Reply
  • Ranger1065 - Wednesday, June 21, 2017 - link

    There has never been a better time to give Intel the middle finger. Reply

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