Section by Dr. Ian Cutress (Orignal article)

Windows Optimizations

One of the key points that have been a pain in the side of non-Intel processors using Windows has been the optimizations and scheduler arrangements in the operating system. We’ve seen in the past how Windows has not been kind to non-Intel microarchitecture layouts, such as AMD’s previous module design in Bulldozer, the Qualcomm hybrid CPU strategy with Windows on Snapdragon, and more recently with multi-die arrangements on Threadripper that introduce different memory latency domains into consumer computing.

Obviously AMD has a close relationship with Microsoft when it comes down to identifying a non-regular core topology with a processor, and the two companies work towards ensuring that thread and memory assignments, absent of program driven direction, attempt to make the most out of the system. With the May 10th update to Windows, some additional features have been put in place to get the most out of the upcoming Zen 2 microarchitecture and Ryzen 3000 silicon layouts.

The optimizations come on two fronts, both of which are reasonably easy to explain.

Thread Grouping

The first is thread allocation. When a processor has different ‘groups’ of CPU cores, there are different ways in which threads are allocated, all of which have pros and cons. The two extremes for thread allocation come down to thread grouping and thread expansion.

Thread grouping is where as new threads are spawned, they will be allocated onto cores directly next to cores that already have threads. This keeps the threads close together, for thread-to-thread communication, however it can create regions of high power density, especially when there are many cores on the processor but only a couple are active.

Thread expansion is where cores are placed as far away from each other as possible. In AMD’s case, this would mean a second thread spawning on a different chiplet, or a different core complex/CCX, as far away as possible. This allows the CPU to maintain high performance by not having regions of high power density, typically providing the best turbo performance across multiple threads.

The danger of thread expansion is when a program spawns two threads that end up on different sides of the CPU. In Threadripper, this could even mean that the second thread was on a part of the CPU that had a long memory latency, causing an imbalance in the potential performance between the two threads, even though the cores those threads were on would have been at the higher turbo frequency.

Because of how modern software, and in particular video games, are now spawning multiple threads rather than relying on a single thread, and those threads need to talk to each other, AMD is moving from a hybrid thread expansion technique to a thread grouping technique. This means that one CCX will fill up with threads before another CCX is even accessed. AMD believes that despite the potential for high power density within a chiplet, while the other might be inactive, is still worth it for overall performance.

For Matisse, this should afford a nice improvement for limited thread scenarios, and on the face of the technology, gaming. It will be interesting to see how much of an affect this has on the upcoming EPYC Rome CPUs or future Threadripper designs. The single benchmark AMD provided in its explanation was Rocket League at 1080p Low, which reported a +15% frame rate gain.

Clock Ramping

For any of our users familiar with our Skylake microarchitecture deep dive, you may remember that Intel introduced a new feature called Speed Shift that enabled the processor to adjust between different P-states more freely, as well as ramping from idle to load very quickly – from 100 ms to 40ms in the first version in Skylake, then down to 15 ms with Kaby Lake. It did this by handing P-state control back from the OS to the processor, which reacted based on instruction throughput and request. With Zen 2, AMD is now enabling the same feature.

AMD already has sufficiently more granularity in its frequency adjustments over Intel, allowing for 25 MHz differences rather than 100 MHz differences, however enabling a faster ramp-to-load frequency jump is going to help AMD when it comes to very burst-driven workloads, such as WebXPRT (Intel’s favorite for this sort of demonstration). According to AMD, the way that this has been implemented with Zen 2 will require BIOS updates as well as moving to the Windows May 10th update, but it will reduce frequency ramping from ~30 milliseconds on Zen to ~1-2 milliseconds on Zen 2. It should be noted that this is much faster than the numbers Intel tends to provide.

The technical name for AMD’s implementation involves CPPC2, or Collaborative Power Performance Control 2, and AMD’s metrics state that this can increase burst workloads and also application loading. AMD cites a +6% performance gain in application launch times using PCMark10’s app launch sub-test.

Hardened Security for Zen 2

Another aspect to Zen 2 is AMD’s approach to heightened security requirements of modern processors. As has been reported, a good number of the recent array of side channel exploits do not affect AMD processors, primarily because of how AMD manages its TLB buffers that have always required additional security checks before most of this became an issue. Nonetheless, for the issues to which AMD is vulnerable, it has implemented a full hardware-based security platform for them.

The change here comes for the Speculative Store Bypass, known as Spectre v4, which AMD now has additional hardware to work in conjunction with the OS or virtual memory managers such as hypervisors in order to control. AMD doesn’t expect any performance change from these updates. Newer issues such as Foreshadow and Zombieload do not affect AMD processors.

X570 Motherboards: PCIe 4.0 For Everybody Test Bed and Setup
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  • FireSnake - Sunday, July 7, 2019 - link

    Awesome!
    I have been waiting for this one.
    Let us start reading.
    Reply
  • WaltC - Sunday, July 7, 2019 - link

    One thing I noticed before I return to the reading is the odd bit about chipsets and memory speeds. Pretty sure the memory controller is on the CPU itself as opposed to the chipset, and I've been running DDR4-3200 XMP CL16 on my Ryzen 1 on both x370 and x470 MSI motherboards with no problems--the same DDR4 2x8 config moved from one motherboard to the next. Reply
  • futrtrubl - Sunday, July 7, 2019 - link

    Guaranteed supported memory speeds and what overclocked memory can generally be used are two very separate things. And yes, that 3200 memory is considered an overclock for the CPU. Reply
  • WaltC - Sunday, July 7, 2019 - link

    Right--so why tie the memory controller to the chipset? QUote: "Some motherboard vendors are advertising speeds of up to DDR4-4400 which until X570, was unheard of. X570 also marks a jump up to DDR4-3200 up from DDR4-2933 on X470, and DDR4-2667 on X370." Almost every x370, x470 motherboard produced will run DDR-4 3200 XMP ROOB. There's an obvious difference between exceeding JEDEC standards with XMP configurations and overclocking the cpu--which I've also done, but that's beside the point. Pointing out present JEDEC limitations overcome with XMP configurations is a far cry from understanding that the chipset doesn't control the memory speeds--the memory controller on the cpu is either capable of XMP settings or it isn't. Ryzen 1 is up to the task. You can also take a gander at vendor-specific motherboard ram compatibility lists to see lots of XMP 3200MHz compatibility with Ryzen 1 (and of course 2k and 3k series). Reply
  • edzieba - Sunday, July 7, 2019 - link

    The new chipset means new boards, to which can be applied more stringent requirements of trace routing for DDR. Same as with the more stringent requirements for PCIe routing for PCIe 4.0. Reply
  • WaltC - Sunday, July 7, 2019 - link

    OK--understood--but improved trace, imo, is mainly for PCIe4.x support with x570-- really not for DDR 3200 support, however, which has already been supported well in x370/x470 motherboards--which I know from practical experience....;) In my case it was as simple as activating the XMP profile #2 in the bios, saving the setting and rebooting. Simply was surprised to see someone tying the mem controller to the chipset! I know that the Ryzen mem controller in the CPU has been improved for Ryzen 3k series, but that has more to do with attaining much higher clocks > 3200MHz for the ram, and is relative to the CPU R 3k series, as opposed to the x570 chipset, since the mem controller isn't in the x570 chipset. All I wanted to say initially is that both DDR 4 3000 & 3200MHz have been supported all the way back to x370 boards, not by the chipset, but by the Ryzen memory controller--indeed, AMD released several AGESA versions for motherboard vendors to implement in their bioses to improve compatibility with with many different brands of memory, too. Reply
  • BikeDude - Sunday, July 7, 2019 - link

    You mentioned 2x8GB. Try with 2x16GB and you might not be as lucky or will have to work harder to get the timing right. Motherboards that only seat two DIMMs will be noticeably easier than four DIMM motherboards.

    If AMD did anything to help grease the wheels, I'm sure many users will appreciate that.

    FWIW, this overclocking guide has helped me a lot: https://www.techpowerup.com/review/amd-ryzen-memor...
    Reply
  • mat9v - Sunday, July 7, 2019 - link

    Does anyone know if 3900X has 3 cores for each CCX (as in 1 core in each CCX disabled) or does it have two CCX's of 4 cores and two CCX's of 2 cores? Reply
  • photonboy - Thursday, July 11, 2019 - link

    3+3 Reply
  • rarson - Monday, July 8, 2019 - link

    WaltC, you're correct. The memory controller is part of the IO die, not the chipset. The chipset is connected to the IO die via 4 PCIe lanes.

    While the subsequent iterations of Ryzen have indeed improved memory support along with the new chipsets, the chipsets have nothing to do with that. I'm assuming the author is using the chipsets to delineate generations of memory improvement, but it could be just as easily (and more clearly) stated by referring to the generation of Ryzen processors.
    Reply

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