Unexpected realtime delay on task 0 on a HP8300

Setting IRQ coalescing only applies to the motherboard Intel MAC
which I assumed you were using, If you are using a Realtek MAC
it makes sense to comment out the IRQ line in the interfaces file
since the Realtek driver does not support that feature.

The problem with Turbo modes  or any mode that dynamically
changes the CPU clock speed is that the processor is halted while
the PLL generated clock frequency stabilizes and this can be
multiple milliseconds

I think it is about time to open the PC and yank out the CPU cooler, clean, repaste, mount, test.

Debian bookworm has excllent support for Secure boot.
However, the "secure" side kicks in if you need to install kernel modules as it is seen you are making an unauthorised change to the kernel code.. This applies if you need to install the Realtek R8168-dkms driver or ethercat.. There is a process to enrol the dkms application in the secure boot  system so it all works nicely.

I just installed debian 12.5 on an office machine this morning that needs secure boot enabled. The installer worked fine.

@PCW & rodw
Error popped up again last night. <grump>

OK - I think this might be something about the realtek driver ?
Purging r8168-dkms  - reinstalling kernel (there is a bug in r8168 so you need to do this)
I get a different driver that I'm testing with now.

modinfo r8169 |grep verm
vermagic:       6.1.0-18-rt-amd64 SMP preempt_rt mod_unload modversions


So the current version in Debian is not the same:
# modinfo r8168 |grep verm
vermagic:       6.1.0-18-rt-amd64 SMP preempt_rt mod_unload modversions

.. Checking - updated pci.ids

I think this is was changed - The old version might have had this misidentified?

 8161  RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller
               10ec 8168  TP-Link TG-3468 v4.0 Gigabit PCI Express Network Adapter

But - the kernel is using r8169?  Not sure why - seems to work - ran some gcode.  

There was a reason that I used the Intel for the LAN - don't remember why now.  If this is still acting strange I will dig up an Intel daughter board.

,.,.,.,.,.,.,.
@rodw
- Re 'secure boot'  - long story - but 'secure boot' as used by Debian appears OK - but the ME + secure-boot is the opposite of secure - the name is quite misleading.   Some hints here:

wiki.gentoo.org/wiki/User:Sakaki/Sakaki%...el_Management_Engine






 

Have you tried disabling EEE with the dkms driver ?

forums.debian.net/viewtopic.php?p=773888...b9703738930a#p773888

Typically, the linux kernel supports the r8169 driver. But this driver is suboptimal and led to ethernet realtime delays.
Installing the r8168-dkms driver is one part of the solution. But the remaining issue is the Debian real time kernel is slow when compared with a kernel compiled from pristine kernel sources.

The simplest solution as sugested before is to use your Intel NIC for communicating with the Mesa card. Test this with the correct coalescing settings as per man hm2_eth. Then look at the energy efficient ethernet settings, followed by the CPU affinity settings discussed in some other threads on this forum.