Re: [PATCH 1/2] x86/resctrl, Documentation: Keep mbm_assign_mode "default" on boot

On Tue, Aug 04, 2026 at 11:05:48PM +0000, Luck, Tony wrote:
> Intel systems have counters backing up every RMID. So CPUD leaf 0xF tells
> Linux how many can be used.

Are you saying that there is not an Intel system out there which has less
counters than RMIDs? If so, that would explain why the exhaustion happens on
AMD only.

/me goes and looks at the SDM:

So there's leaf 0 there:

EBX[31:0]	MAX_RMID	Maximum range (zero-based) of RMID within this
physical processor of all types.

I'm assuming that means you have so many RMIDs and all of them are backed by
counters.

And if we look at one example if Emerald Rapids:

CPUID 0000000F: 00000000-0000007F-00000000-00000002 [SL 00]
CPUID 0000000F: 00000008-00008000-0000007F-00000007 [SL 01]

https://instlatx64.github.io/InstLatx64/GenuineIntel/GenuineIntel00C06F2_EmeraldRapids_02_CPUID.txt

That 0x7f there means 128 counters for 128 RMIDs so there cannot be any
exhaustion.

Am I close?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette