Application performance dropped after upgrade to RHEL 8.5

Solution Verified - Updated -


  • After updating the system to RHEL 8.5 (kernel-4.18.0-348) the application is showing significant performance drop.

    The application vendor found that in older kernel, the read_ahead_kb value was 128 KB:

    $ cat /sys/block/sdb/queue/read_ahead_kb

    But after update to 8.5 kernel, the system is using 32 MB read_ahead_kb value:

    $ cat /sys/block/sdb/queue/read_ahead_kb

    Changing the read_ahead_kb count back to 128 KB fixes the performance issue.

  • We would like to understand why the newer kernel is setting different read_ahead_kb value?


  • Red Hat Enterprise Linux 9
  • Red Hat Enterprise Linux 8.5
    • kernel-4.18.0-348 and later

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