Tuesday, October 12th 2021
First Windows 11 Patch Tuesday Makes Ryzen L3 Cache Latency Worse, AMD Puts Out Fix Dates
Microsoft on October 12 put out the first Cumulative Updates for the new Windows 11 operating system, since its October 5 release. The company's monthly update packages for Windows are unofficially dubbed "patch Tuesday" updates, as they're scheduled to come out on the second Tuesday of each month. Shortly after Windows 11 launch, AMD and Microsoft jointly discovered that Windows 11 is poorly optimized for AMD Ryzen processors, which see significantly increased L3 cache latency, and the UEFI-CPPC2 (preferred cores mechanism) rendered not working. In our own testing, a Ryzen 7 2700X "Pinnacle Ridge" processor, which typically posts an L3 cache latency of 10 ns, was tested to show a latency of 17 ns. This was made much worse with the October 12 "patch Tuesday" update, driving up the latency to 31.9 ns.
AMD put out a statement on social media, which surfaced on Reddit. The company stated that patches for the two issues have been developed, and specified dates on which they'll be released. The patch for the Preferred Cores (UEFI-CPPC2) bug will be released on October 21. Customers can request the patch even earlier. By "customers," AMD is probably referring to big enterprise customers running mission-critical applications on Threadripper or EPYC-powered workstations. The L3 cache latency bug will be fixed through the Windows Update channel, its release is scheduled for October 19.
If rumors surrounding the late-October/early-November launch dates of 12th Gen Intel Core "Alder Lake" processors are true, then the situation with these patches will have a direct impact on AMD. Processor reviewers will be compelled to use Windows 11 for their Core "Alder Lake" testing, as the new operating system supposedly has greater awareness of the heterogeneous core design. The switch to Windows 11 will force a re-bench of all processors, including the AMD Ryzen chips. With AMD cautioning of an up to 15% performance hit from the added cache latency and Preferred Cores bugs, results of AMD processors in 12th Gen Core launch reviews could be affected. It is advisable for AMD to reach out to the press with these patches immediately, if they are ready.
Source:
destiny2sk (Reddit)
AMD put out a statement on social media, which surfaced on Reddit. The company stated that patches for the two issues have been developed, and specified dates on which they'll be released. The patch for the Preferred Cores (UEFI-CPPC2) bug will be released on October 21. Customers can request the patch even earlier. By "customers," AMD is probably referring to big enterprise customers running mission-critical applications on Threadripper or EPYC-powered workstations. The L3 cache latency bug will be fixed through the Windows Update channel, its release is scheduled for October 19.
157 Comments on First Windows 11 Patch Tuesday Makes Ryzen L3 Cache Latency Worse, AMD Puts Out Fix Dates
I mean, obviously something's going on, since the patch is all but ready, but I just don't understand what happened.
Is it like, rapidly thread switching triggering constant l3 updates on Ryzen? Or what? What could even cause this?
It's either super incompetent, or super suspicious, that's for sure.
13th October Windows 11:
And just for compare Window 10 (about June 2021):
It's even free to upgrade from windows 10, so the deal here is convince the user at any cost to upgrade so to stop other people/nations to snoop around, except for them of course.
Whoopsiedaisy! We broke that whatchamacallit for AMD!
Aw shucks, they shouldn't need that right?
Well heck, we'll have to think on it for a couple of months so we fix it jusst right!
missed the windows 7 smooth OS ever made, clean and fast
As I understand it, this is a change that was made to the thread and execution schedules within the Windows 11 Kernel that were supposed to increase performance and efficiency across the board for all CPU types, but for Ryzen CPU's, and the unique way the CCX handles instructions and code allocations in combination with the way the CPU complex buffers data in&out of the L3 cache, the changes introduced a scheduling mis-match in the prediction branches which then have to be flushed, reallocated and then the fetch functions have to be recalculated without any prediction functions. This is causing delays in instruction processing for data being cached in L3. This does not happen for data stored in L1 or L2 cache.
This problem is also limited to certain types of instructions which is why the performance degradation only seems to exhibit itself in certain scenario's on Ryzen based CPU's. In programs that do not trigger the problem, performance is unaffected and is either indentical to that which would happen in Windows 10, or is improved upon as originally intended.
So this is a complex problem neither microsoft, nor AMD saw coming. The confidence in fixing the problem is high, so it would seem to be only a matter of time and not very long.
So the question is, do intel tell reviewers what OS and what patches they have installed before testing? and if yes how is that acceptable?
What we see here is an way higher abstraction of what happens at silicon level. Crude example/oversimplification - cache may be 'busy' dealing with some other 'transaction', hence it will look like it's slow, i.e. latency is raised.
The core preference stuff, i can absolutely just see that as a normal situation with a driver coming right after launch. THAT seems innocent enough.
and the problem fixed now in the win11 dev channel
A lot of review sites will have decided to run the benches already for their reviews, getting the Windows 11 based values they will use done first for products already on the market. AMD absolutely needs their PR to engage with these sites and ensure they use the patched version of Windows 11, even if it means re-running the benches. Or at least use the Windows 10 results for AMD CPUs if they don't have time.
Many sites run the benches once and use them for a long time afterwards, so this is pretty critical for AMD.
Wintel is back.
The theory that, microsoft can be bribed by intel to favour them is just ridicilous and beyond rational thinking.
What is possible is that AMD have always been historically slow mover in patches and security. It is safe to say embedded into their dna.