[PlanetCCRMA] kernel-rt latency issues

[Rob Wallace]

Recently I've been evaluating the real-time PREEMPT_RT patch. I noticed that PlanetCCRMA already had RPM packages so I thought I would try them out.

When I ran the 'cyclictest' on the ccrma kernel I noticed a lot of latency and jitter. This didn't seem normal compared to the PREEMPT_RT kernel I built myself. After investigating the issue I found certain kernel options in the ccrma kernel that should not be selected for a real-time system. These are the kernel options I changed to fix the latency issue in your build:

# CONFIG_SUSPEND is not set
# CONFIG_HIBERNATION is not set
# CONFIG_PM_RUNTIME is not set
# CONFIG_PM_DEBUG is not set
CONFIG_ACPI_AC=m
CONFIG_ACPI_BATTERY=m
CONFIG_ACPI_BUTTON=m
CONFIG_ACPI_FAN=m
CONFIG_ACPI_PROCESSOR=m
CONFIG_ACPI_THERMAL=m
CONFIG_ACPI_CONTAINER=m
# CONFIG_CPU_FREQ is not set
# CONFIG_INTEL_IDLE is not set
CONFIG_POWER_SUPPLY=m
CONFIG_HWMON=m

You can try a before and after test to see the difference. I ran the cyclictest as follows:
cyclictest -a2 -m -n -I -i 100 -p 80

Cheers,
Rob

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