Tuesday, September 6th 2016
SMT and Power Management Behind "Kaby Lake" and "ZEN" Windows 10 Restrictions
Microsoft recently sparked a stir when it was reported that the company will support upcoming CPU architectures by Intel and AMD only on Windows 10, with the keyword being "support" and not "compatibility." This means that Microsoft will offer customer-support and likely serve updates to Intel "Kaby Lake" and AMD "ZEN" machines only running Windows 10 (and its enterprise variant Windows Server 2016, based on the NT 10 kernel), and not older versions of Windows. The processors themselves are compatible with any x86 operating system, Windows or *nix, 32-bit or 64-bit. HotHardware dug out the likely causes of this decision.
Apparently, new power-management and SMT features are behind the decision. With its "Kaby Lake" microarchitecture, Intel is introducing a new power-management feature called Speed Shift Technology. This lets the processor adjust its clock-speed to match processing loads at response time of 15 ms. This likely requires OS-level hooks, so the on-die power-management components can poll for processing loads and accordingly raise or lower clock-speeds 66.66 times each second, at no CPU cost. In its ZEN microarchitecture reveal, AMD too spoke about fine-grained, multi-domain clock-gating (≠ power-gating) on its "ZEN" based processors, such as "Summit Ridge."
AMD "ZEN" processors introduce simultaneous multi-threading, a feature that exposes each physical core as two logical CPUs to the OS, for better utilization of on-die resources. Intel's implementation of SMT is the HyperThreading Technology (HTT), and has been around for over a decade. AMD's SMT implementation isn't identical to that of HyperThreading, with the two threads on a CPU competing for resources in a method unique to AMD. This can't work without the OS kernel and scheduler being aware of the method. You'll remember that Microsoft had to update the kernel and scheduler of Windows 7 in a similar way, to optimize it for "Bulldozer."
These, HotHardware argues, could be the likely reasons why Microsoft is limiting support for the new CPU microarchitectures to Windows 10.
Source:
HotHardware
Apparently, new power-management and SMT features are behind the decision. With its "Kaby Lake" microarchitecture, Intel is introducing a new power-management feature called Speed Shift Technology. This lets the processor adjust its clock-speed to match processing loads at response time of 15 ms. This likely requires OS-level hooks, so the on-die power-management components can poll for processing loads and accordingly raise or lower clock-speeds 66.66 times each second, at no CPU cost. In its ZEN microarchitecture reveal, AMD too spoke about fine-grained, multi-domain clock-gating (≠ power-gating) on its "ZEN" based processors, such as "Summit Ridge."
These, HotHardware argues, could be the likely reasons why Microsoft is limiting support for the new CPU microarchitectures to Windows 10.
57 Comments on SMT and Power Management Behind "Kaby Lake" and "ZEN" Windows 10 Restrictions
This is purely a scare tactic anyway. Intel have sometimes toed the 'Wintel' line before, aligning with MS, but I doubt they do here, and AMD certainly won't.
There's a roughly 0% chance of AMD not writing drivers for W7 and W8(.1) for Zen. They want to sell chips and regain market share. They're not concerned with MS' shenanigans.
I'd say there's less than 20% chance of Intel not releasing them, because if they don't, then they lose all those sales W7 and W8.1 sales to AMD.
Indeed, MS will most likely climb down quickly themselves when the time comes, when large companies tell them they'll be moving to 'nix.
Large companies have started moving to Win10, or at least have pilots running. Trust me, there won't be mass exodus to Linux.
RHEL on the other hand has a 7-10 year support length, with shorter intermediary phases that you are supposed to intermediately upgrade to (very Windows 10-like actually). On those versions, you also skip a lot of feature upgrades, and in order for their support cycle to work at all, RH (and others) spend a lot of time and money backporting stuff from newer bits.I've heard this batch of arguments around 2006-2009 when people were clinging to their XP machines like limpets. I've heard the same around the early 2000s when XP launched and people clung to their 98SE machines just as hard. Happens every cycle, and every time they suck it up eventually or move away from Windows.
For a lot of companies, moving away from Windows isn't really much of an option. Between Windows-only software (Active Directory, MSOffice, Exchange for example), support contracts (commercial support for RHEL or Debian ain't free... and if you don't have a support contract, you almost always need to hire in-house talent to do it for you), the cost of porting stuff/migrating to new equivalent solutions, training employees and other things I've probably forgotten, it just doesn't make sense.