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)
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150 Comments on First Windows 11 Patch Tuesday Makes Ryzen L3 Cache Latency Worse, AMD Puts Out Fix Dates

#26
HD64G
After that mess, I think that the only way of a fair comparison for the upcoming AL reviews would be to post the AMD CPUs results both on win10 and win11 to compare with AL on win11. That would totally backfire for MS. But that needs some balls to be done...
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#27
bug
I'm still trying to understand how the OS controls cache latency.
I mean, obviously something's going on, since the patch is all but ready, but I just don't understand what happened.
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#28
R-T-B
bugI'm still trying to understand how the OS controls cache latency.
I mean, obviously something's going on, since the patch is all but ready, but I just don't understand what happened.
I have a hard time with this too.

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.
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#29
Ziggy1971
HD64GAfter that mess, I think that the only way of a fair comparison for the upcoming AL reviews would be to post the AMD CPUs results both on win10 and win11 to compare with AL on win11. That would totally backfire for MS. But that needs some balls to be done...
Sorry, but I think any and all leaks, rumors, reviews etc. are completely pointless and invalid until people can reliably run fair tests for all parties.
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#30
emigrant
So on my side (6th October) Windows 11 :


13th October Windows 11:


And just for compare Window 10 (about June 2021):
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#31
Luminescent
I'm gonna make some wild assumptions here that Windows 10 got to easy to hack along with the latest exploits and Microsoft decided they need to make Windows 11 so only them and few others could continue to have access.
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.
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#33
R-T-B
LuminescentI'm gonna make some wild assumptions here that Windows 10 got to easy to hack along with the latest exploits and Microsoft decided they need to make Windows 11 so only them and few others could continue to have access.
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.
That... literally has nothing to do with this?
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#34
maxfly
Alright boys, Were going to build this thingamabob for AderLake!
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!
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#35
xtreemchaos
we all know MS has to get it wrong many times before they get it right its par the course, i mean how long have we win 10 ? and only the last year or so its been performing 99% as it should now MS wants us suckers to go through it again with 11. i have 2 riggs that will run 11 on there terms but no thanks MS id like them to stick it where the sun dont shine for a few more years :) .
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#36
viandyka
Microsoft and BUGS,, windows 10 is never completed then make new OS

missed the windows 7 smooth OS ever made, clean and fast
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#37
bug
R-T-BI have a hard time with this too.

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.
That would only cause cache thrashing (which will impact performance), but it wouldn't change latency. Latency is supposed to be a physical trait of the chip... :confused:
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#38
lexluthermiester
CrackongWindows update break things again and even worse.....surprised ?
For once, this is not the fault of Windows update screwing things up.

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.
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#39
chrcoluk
I think reviewers shouldn't be compelled to do anything, if they are it means its not an independent review, the intel processors I would like to see tested on Windows 10 as that's currently the mainstream OS used by the majority of desktop users.

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?
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#40
FireFox
The Power Of Intel
CrackongWindows update break things again and even worse.....surprised ?
Did anyone force you to buy AMD?
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#41
zlobby
bugLatency is supposed to be a physical trait of the chip... :confused:
No. A physical trait would be time needed for an individual transistor to switch a circuit. The rest is a byproduct.

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.
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#42
lexluthermiester
LuminescentI'm gonna make some wild assumptions here that Windows 10 got to easy to hack along with the latest exploits and Microsoft decided they need to make Windows 11 so only them and few others could continue to have access.
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.
Nonsense. This was a profit motivated attempt at a power grab, plain & simple. The microsoft store is what microsoft wants to turn into a similar money maker of the Apple store and Google Play. That's it, money and control. I have been testing Windows 11 extensively and have found no vulnerabilities once the OS is PROPERLY configured.
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#43
Mussels
Moderprator
bugI'm still trying to understand how the OS controls cache latency.
I mean, obviously something's going on, since the patch is all but ready, but I just don't understand what happened.
My guess is security fixes and tweaks for them, like the fixes for specter and meltdown but affecting the wrong CPUs.


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.
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#44
Roberto.
‎AMD A9-9420 RADEON R5, 5 CORE PROCESSING 2C+3G 3.00 GHz this type of processor will receive a patch... Thank you..‎
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#45
adel abdo
I have told Microsoft about this problem 6 months ago with no reply
and the problem fixed now in the win11 dev channel
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#46
Sykobee
It does seem odd, how Intel works with Microsoft to optimise Windows for AlderLake's topology, and as a side effect performance on AMD processors which was fine under Windows 10, has dropped.

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.
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#47
lexluthermiester
SykobeeIt does seem odd, how Intel works with Microsoft to optimise Windows for AlderLake's topology, and as a side effect performance on AMD processors which was fine under Windows 10, has dropped.
Those two things are not related. Kernel level drivers are created for CPUs just like any other piece of hardware and the code is compiled for each as needed for the capability of each CPU family. These problems are very specific to the way Windows interacts with Ryzen CPU's. It is not related to anything Intel.
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#48
stimpy88
So anyone wanna bet that all Alder Lake benchmarks (that compare to a Ryzen CPU) are done on the release version, or build 258 of Windows 11???

Wintel is back.
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#49
Turmania
Do we even know alder lake performing at optimum with windows 11 yet?
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.
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#50
lexluthermiester
stimpy88So anyone wanna bet that all Alder Lake benchmarks (that compare to a Ryzen CPU) are done on the release version, or build 258 of Windows 11???

Wintel is back.
Oh, please. Can we have done with this kind of fanboy nonsense already?
TurmaniaThe theory that, microsoft can be bribed by intel to favour them is just ridiculous and beyond rational thinking.
Exactly! Especially considering that microsoft is a HUGE AMD customer with the XBox using AMD SOC's exclusively!
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