Q: 2.8 from buildbot don't recognize PREEMPT_RT kernel

Hi !

I have installed stock (from buildbot repository stretch/2.8-rtpreempt) 2.8.0~pre1.5197.g08c06a0f9, and its seems it doesn't recognize that this kernel from Debian repository (4.9.0-11-rt-amd64) have PREEMPT_RT feature. Latency test shows huge 1588779 ns jitter for 25us thread. Runnung same PC with LinuxCNC 2.7 Live shows 21516 ns max jitter.

Installed 5.2-rt from testing, same problem.

How to fix this problem ?

Thanks in advance.

Intel Quad Core 2.4GHz Q6600, 8GB RAM, Gigabyte P35-DS4 m/b, Geforce GT630, SSD 120GB.
Someday it was my workstation which still has parallel port header, retired several years ago.

Grub boot options
quiet splash lapic idle=poll acpi_irq_nobalance noirqbalance noht isolcpus=1,2,3
drm_kms_helper.poll=0

I suspect linuxcnc from buildbot requires *exact* same kernel when it was compiled, not sure if I'm correct here.

BTW, changing grub boot options had little to no effect, latency is *huge* as with plain non-rt kernel.

GeFoce GT630, driver is nouveau.

Fresh install of Debian 9 with MATE desktop (ISO from Debian site). Disabled whatever possible, incl. animation in MATE desktop.

This is really strange - running LinuxCNC Live on the same PC doesn't show this latency problem.

Maybe the harddisk is dying and messing up latency?

If you want Debian 9 with preempt-rt why not use the Linuxcnc ISO?
www.linuxcnc.org/testing-stretch-rtpreempt/

HDD is WD SSD, and it is fine.

At first, I supposed it was problem with nVidia GT630 and nouveau driver.
I replaced GT630 with Radeon HD6450, as suggested here (post #418):
www.cnc-club.ru/forum/viewtopic.php?f=15&t=1078&start=400

Latency is still horrible.
I disabled onboard audio, firewire, tweaked grub kernel params - all same,

Finally, I found this thread, which describe latency spikes on Gigabyte P35-DS3 and DS4.
forums.tomshardware.com/threads/audio-la...ith-p35-ds3r.411939/

Its a buggy m/b BIOS after all.

I'll simply trash this m/b, its very old anyway, and buy something else.

Hope this info will be useful for someone.

Yes, I re-flashed latest available F14, no changes.

Here is another thread with similar latency issues, looks like the whole P35 family of Gigabyte m/b have been problematic.

forums.anandtech.com/threads/gigabyte-bo...-dpc-latency.171880/

Replacement m/b cost close to nothing, the most cumbersome part is a re-assembly.