PH52860: HIGH CPU WHILE AT OR NEAR MAXCLIENTS

APAR status

• Closed as program error.

Error description

• IHS on zOS or linux might demonstrate high CPU while at or near
  MaxClients.
  
  The high CPU is caused by repeated calls to asyico, msgrcv, or
  epoll system calls.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:  All users of IBM HTTP Server on Linux and   *
  *                  zOS                                         *
  ****************************************************************
  * PROBLEM DESCRIPTION: IHS on z/OS or linux, using the event   *
  *                      MPM, might show high CPU while at or    *
  *                      near MaxClients.                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  Typically, MaxClients is reached when there is some backend
  hang
  and the webserver itself does very little work while it waits.
  T
  In these cases, negligible CPU usage is used.
  While waiting, IHS may continually pause and resume the
  listening sockets in each overloaded process, but the "resume"
  can be premature due to a programming error related to unsigned
  integer arithmetic.  This can result in high CPU as the
  pause/resume are system calls called in a tight loop.
  

Problem conclusion

• The code was updated to avoid the premature "resume" of listenin
  sockets and errors/trace for related conditions were improved.
  
  The fix for this APAR is targeted for inclusion in IBM HTTP
  Server fix packs 9.0.5.16. For more information, see 'Recommende
  Updates for WebSphere Application Server':
  https://www.ibm.com/support/pages/node/715553
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  IBM HTTP SERVER

• Fixed component ID

  5724J0801

Applicable component levels