[Bug 247602] top occasionally shows unrealistic WCPU values

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=247602

            Bug ID: 247602
           Summary: top occasionally shows unrealistic WCPU values
           Product: Base System
           Version: 11.4-RELEASE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: bin
          Assignee: bugs at FreeBSD.org
          Reporter: jdc at koitsu.org

Preface: this is a different problem than what's in PR 135823 (threading is not
involved in this one, at least not as far as the processes themselves go), and
what's in PR 236096 (I use SCHED_ULE).  (I've picked 11.4-RELEASE for the
Version field in Bugzilla because that's the closest to stable/11 I can get.)

While building world (make -j2 buildworld) on a 2-core 11/stable (r358258)
amd64 VM I have, while running top -s 1, I noticed  on very rare occasion --
but recurring -- some procesesses would show completely ridiculous WCPU values.
 The numbers of processes which would show this varied (sometimes an entire
page worth, other times only partial numbers).  Most of these processes do not
have threads, in case that's relevant.  Example:

  PID USERNAME    THR PRI NICE   SIZE    RES STATE   C   TIME    WCPU COMMAND
 1211 halbot        1  20    0 56524K 50092K select  1   0:01
1830297421127995.00% perl /home/halbot/hal/halbot.pl
/home/halbot/hal/halbot.json
  764 jdc           1  20    0 13208K  5748K select  0   0:00
1830297421127995.00% sshd: jdc at pts/0 (sshd)
  486 unbound       1  20    0 19320K  9672K kqread  1   0:00
1830297421127995.00% /usr/local/sbin/unbound -c
/usr/local/etc/unbound/unbound.conf
  905 root          1  20    0  5024K  1372K select  1   0:00
1830297421127995.00% make -m /usr/src/share/mk -f Makefile.inc1 TARGET=amd64
TARGET_ARCH=amd64 buildworld
  881 root          1  20    0  5024K   984K select  1   0:00
1830297421127995.00% make -j2 buildworld
 4091 root          1  52    0  5024K  1780K select  1   0:00
1830297421127995.00% make DIRPRFX=usr.bin/clang/llvm-tblgen/ all
  465 root          1  20    0  6428K  1996K select  1   0:00
1830297421127995.00% /usr/sbin/syslogd -4 -s -s -cc
 4240 root          1  80    0   156M   135M CPU1    1   0:03 100.71%
/usr/bin/c++ -cc1 -triple x86_64-unknown-freebsd11.3 -emit-obj -disable-free
-disable-llvm-verifier -discard-value
 4237 root          1  80    0   164M   142M RUN     0   0:04  99.76%
/usr/bin/c++ -cc1 -triple x86_64-unknown-freebsd11.3 -emit-obj -disable-free
-disable-llvm-verifier -discard-value
 4216 jdc           1  20    0  7928K  2900K CPU0    0   0:00   0.09% top
  568 root          1  20    0   105M 95940K select  1   0:02   0.03%
/usr/local/bin/perl -T -w /usr/local/bin/spamd -4 -c -d -r
/var/run/spamd/spamd.pid
 1493 jdc           1  20    0 13208K  5776K select  1   0:00   0.02% sshd:
jdc at pts/1 (sshd)
  656 root          1  20    0   145M  6172K kqread  0   0:00   0.01% php-fpm:
master process (/usr/local/etc/php-fpm.conf) (php-fpm)
...


This looks like an overflowed integer, but makes me wonder if the bug is in the
kernel or in top itself.  (Not sure if this should be Component: bin or
Component: kern)

I might suggest pulling jhb@ in for this one since he has great familiarity
with some of top's code, esp. relating to WCPU.

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