Chapter 5. Important changes to external kernel parameters

This chapter provides system administrators with a summary of significant changes in the kernel distributed with Red Hat Enterprise Linux 9.9. These changes could include, for example, added or updated proc entries, sysctl, and sysfs default values, boot parameters, kernel configuration options, or any noticeable behavior changes.

New kernel parameters

Override selected exit-latency and target-residency values in the CPU-specific C-state table.

Format: state:exit_latency:target_residency[,state:exit_latency:target_residency…​]

Latency and residency values are expressed in microseconds. Empty fields preserve the existing value. For example, intel_idle.table="C6::400" changes only the target residency of the C6 state. The kernel validates the supplied values before using them.

Control whether the mpt3sas driver sends TEST UNIT READY and START UNIT commands while bringing devices to the ready state during unblock processing. The default is 1, which preserves the previous behavior.

Control the number of retries during device discovery and readiness checks. This setting can improve discovery of slow or transient SAS and PCIe devices.

Override the SoC slider value used by the balanced platform profile for the Intel INT340x thermal driver. The default slider value is 3. A value changed after module load takes effect the next time balanced is written to the platform-profile sysfs attribute. Values that overlap the performance value 0 or the power-saver endpoint are rejected.

Bypass the check that requires the pad3 field in an MD superblock to be zero. This permits assembly of arrays created with newer metadata features that use this field.

Control evaluation of LPS0 _DSM Function 1 and checking of the resulting constraints during suspend-to-idle diagnostics. This avoids potentially problematic firmware evaluation when LPS0 constraint diagnostics are not required.

Changed kernel parameters

Control Intel telemetry event groups through the rdt= boot parameter. The parameter now accepts perf and energy to force activation of all Intel telemetry event groups of the selected type. Prefix the selector with ! to disable the event groups. A :guid suffix restricts the operation to one event group.

For example:

rdt=perf

rdt=!energy

rdt=perf:<guid>

Telemetry event groups with too few hardware counters for all resource monitoring identifiers (RMIDs) are disabled by default. Explicitly enabling such a group limits the number of monitor groups to the smallest available hardware-counter count.

Control the Intel Sound Open Firmware Bluetooth link mask. The parameter now accepts 0 so that users can disable a Bluetooth link that firmware reports through the NHLT table.

Removed kernel parameters

Control C1/C1E preference on Alder Lake. This parameter affected only Alder Lake, where C1E was already the default, and had no effect on other platforms.

Control 40 MHz operation in the 2.4 GHz band for the rtl8xxxu driver. 40 MHz operation in the 2.4 GHz band is now enabled by default. To disable it globally, use the existing cfg80211.cfg80211_disable_40mhz_24ghz parameter.

Invalidate cached directory entries for the CIFS client. When CONFIG_CIFS_DEBUG is enabled, write 0 to the existing open_dirs procfs entry instead.

New sysctl parameters