Why does the 'elevator=' parameter no longer work in RHEL8

Environment

• Red Hat Enterprise Linux 8

Issue

• Tried to set the I/O scheduler using elevator=bfq on the grub line, but it did not change the scheduler

[root@host]# cat /proc/cmdline 
BOOT_IMAGE=(hd0,msdos1)/vmlinuz-4.18.0-57.el8.x86_64 root=/dev/mapper/rhel-root ro crashkernel=auto resume=/dev/mapper/rhel-swap rd.lvm.lv=rhel/root rd.lvm.lv=rhel/swap transparent_hugepage=never elevator=kyber

[root@host]# cat /sys/block/sdc/queue/scheduler 
[mq-deadline] kyber bfq none

Resolution

• The elevator= parameter was used for single-queue I/O schedulers. With the newer multi-queue I/O schedulers such as mq-deadline, bfq, and kyber, the parameter does not function. If needed, the scheduler can still be edited by using a tuned profile, echo'ing in the desired value, or creating a udev rule set.

  • As an alternate to elevator=, please see:
    • How to persistently set the I/O scheduler
    • This content is not included.How to create a customized tuned profile

• A private RFE This content is not included.Bug 1665295 - RFE - add elevator= option for multiqueue elevators has been opened to get the parameter back in.

  • For information on this RFE, please contact Red Hat Support

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