[RHEL 8] sar is not capturing %gnice value for isolated CPUs(with parameter nohz_full for isolated CPUs) intermittently and %idle is shifted to %gnice column

Solution Verified - Updated -

Issue

  • For isolated CPUs(with parameter nohz_full is enabled for isolated CPUs), sar is not capturing %gnice continuously and %idle is shifted to %gnice column.

  • Example of kernel command line:

isolcpus=1-3,5,7-15 nohz=on nohz_full=1-3,5,7-15
  • When the process is moved to/launched on an isolated CPU, per second CPU utilization from sar looks like below:
# sar -u ALL -P 13 1

04:10:41 PM     CPU      %usr     %nice      %sys   %iowait    %steal      %irq     %soft    %guest    %gnice     %idle
04:10:42 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:43 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:44 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:45 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:46 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:47 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00           <<----
04:10:48 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:49 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:50 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:51 PM      13    100.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00
04:10:52 PM      13    100.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00
04:10:53 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:54 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:55 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:56 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:57 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:58 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:10:59 PM      13    100.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00
04:11:00 PM      13    100.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00
04:11:01 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:11:02 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:11:03 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:11:04 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:11:05 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:11:06 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:11:07 PM      13    100.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00
04:11:08 PM      13    100.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00
04:11:09 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:11:10 PM      13     84.15      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00     15.85
04:11:11 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00
04:11:12 PM      13      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00      0.00    100.00

Environment

  • RHEL 8.3 and prior versions of RHEL 8.
  • sysstat-11.7.3-5.el8.x86_64 and prior versions of sysstat on RHEL 8.
  • Isolated CPUs and nohz_full parameter enabled for isolated CPUs.

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