Red Hat Enterprise Linux Diagnostics and Troubleshooting

Instructions

The servera system has an attached SAS RAID array that uses the megaraid_sas.ko kernel module. Unfortunately, performance is unpredictable, and sometimes error messages about MSI-X interrupts appear in the logs.

After opening a support case, you are asked to disable MSI-X interrupt handling in the driver to test whether this configuration fixes the issue.

1. Log in to servera and switch to the root user.

   [student@workstation ~]$ ssh student@servera
   ...output omitted...
   [student@servera ~]$ sudo -i
   [sudo] password for student: student
   [root@servera ~]#

2. View the kernel module options for the megaraid_sas.ko kernel module. Locate the option for MSI-X interrupt handling, load the module, and verify that this option is applied. Unload the module before continuing.

   1. View the options for the megaraid_sas.ko kernel module:

      [root@servera ~]# modinfo -p megaraid_sas
      lb_pending_cmds:Change raid-1 load balancing outstanding threshold. Valid Values are 1-128. Default: 4 (int)
      max_sectors:Maximum number of sectors per IO command (int)
      msix_disable:Disable MSI-X interrupt handling. Default: 0 (int)
      msix_vectors:MSI-X max vector count. Default: Set by FW (int)
      allow_vf_ioctls:Allow ioctls in SR-IOV VF mode. Default: 0 (int)
      ...output omitted...

   2. Locate the MSI-X interrupt handling option.

      [root@servera ~]# modinfo -p megaraid_sas | grep -i msi
      msix_disable:Disable MSI-X interrupt handling. Default: 0 (int)
      msix_vectors:MSI-X max vector count. Default: Set by FW (int)

      The msix_disable option is the relevant choice.

   3. Load the megaraid_sas.ko kernel module manually.

      [root@servera ~]# modprobe -v megaraid_sas
      insmod /lib/modules/4.18.0-305.el8.x86_64/kernel/drivers/scsi/megaraid/megaraid_sas.ko.xz

   4. Verify that the msix_disable default (value 0) is the current value.

      [root@servera ~]# cat /sys/module/megaraid_sas/parameters/msix_disable
      0

   5. Unload the megaraid_sas.ko module.

      [root@servera ~]# modprobe -rv megaraid_sas
      rmmod megaraid_sas

3. Configure the megaraid_sas.ko module to always set msix_disable=1. This option is applied whether the module is loaded manually or automatically. For easy copying of this configuration to other systems, use a separate configuration file. Verify that the new configuration is applied correctly.

   1. Create a file called /etc/modprobe.d/megaraid.conf with the following entry:

      options megaraid_sas msix_disable=1

   2. Load the megaraid_sas.ko kernel module.

      [root@servera ~]# modprobe -v megaraid_sas
      insmod /lib/modules/4.18.0-305.el8.x86_64/kernel/drivers/scsi/megaraid/megaraid_sas.ko.xz msix_disable=1

   3. Verify that your new setting is applied correctly.

      [root@servera ~]# cat /sys/module/megaraid_sas/parameters/msix_disable
      1

4. Return to workstation as the student user.

   [root@servera ~]# exit
   [student@servera ~]$ exit
   [student@workstation ~]$