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Description of problem:
When running hwlatdetect on the RT kernel it can only pass when the realtime-virtual-host tuned profile is applied. Attempting to manually apply only the kernel command line parameters from realtime-virtual-host does not result in a passing test.
Version-Release number of selected component (if applicable):
kernel = 3.10.0-1040.rt56.999.el7.x86_64
rt-tests = rt-tests-1.0-15
tuned = tuned-profiles-nfv-host-2.11.0-2.el7.noarch
How reproducible:
Always
Steps to Reproduce:
1. install rt-kernel and rt-tests and reboot
2. run hwlatdetect
Actual results:
High (>10us) samples are reported. When the realtime-virtual-host profile is applied then no samples are reported.
Expected results:
No samples should be reported.
Additional info:
Created attachment 1564769[details]
Patch to disable c-states while detector is running
This patch uses the /dev/cpu_dma_latency mechanism to disable c-state transitions while the hwlatdector script is running.
I pulled down the git repo for rt-tests and using the unstable branch I tested with and without Clark's c-state patch. Without the patch I still see 13us max latency with hwlatdetect. With the patch I get 6us max latency (using --threshold=1).
Note: on this system (Dell R740xd with Intel Xeon Gold 6130) both C1E and C-States are explicitly disabled in the BIOS/UEFI interface.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2019:2210