'sar -u ALL' reports an overflow value

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 6
  • sysstat-9.0.4-11.el6.x86_64

Issue

  • "sar -u ALL -P ALL 1 1000" reports an overflow value as follows.
    # sar -u ALL -P ALL 1 1000
 Linux 2.6.32-70.el6.x86_64 (shiro-kumarl)       09/08/10        _x86_64_        (8 CPU)
 ...
 14:42:02        CPU      %usr     %nice      %sys   %iowait    %steal      %irq     %soft    %guest     %idle
 14:42:03        all      2.46      0.00      3.04      0.82      0.00      0.00      0.00      0.23     93.45
 14:42:03          0      5.94      0.00      8.91      0.99      0.00      0.00      0.00      0.00     84.16
 14:42:03          1      4.55      0.00      2.27      0.00      0.00      0.00      0.00      1.14     92.05
 14:42:03          2      2.83      0.00      1.89      0.00      0.00      0.00      0.00      0.00     95.28
 14:42:03          3      0.98      0.00      3.92      0.00      0.00      0.00      0.00      0.00     95.10
 14:42:03          4      3.74      0.00      6.54      2.80      0.00      0.00      0.00      0.00     86.92
 14:42:03          5      1.96      0.00      1.96      0.00      0.00      0.00      0.00      0.00     96.08
 14:42:03          6    5506368326.92      0.00      1.28      2.56      0.00      0.00      0.00      1.28     96.15
 14:42:03          7      0.58      0.00      0.00      1.17      0.00      0.00      0.00      0.00     98.25
 ....
  • A value of %usr for CPU 6, 5506368326.92, is an overflow value.

Resolution

Root Cause

  • There is a case that the value of guest is incremented but the value of user is not incremented in /proc/stat.
  • In kernel, when the guest is accounted, the user also is accounted at the same time in account_guest_time() of kernel.
  • But, when the value outputed to /proc/stat actually is culculated, there is a case that the value of user is not incremented although the value of guest is incremented.

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