OA61558: POLL FUPT LATCH ENHANCEMENT

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Customer reported application delay. One of the delays
  was caused by poll process-level FUPT latch.
     Poll obtains FUPT latch exclusive three times. Concurrent
  poll requests from multiple threads within the same process
  generated FUPT latch contention in latchset
  SYS.BPX.A000.FSLIT.FILESYS.LSN, causing application delay.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All users of z/OS UNIX System Services for                   *
  * HBB77B0 HBB77C0 and HBB77D0 using                            *
  * poll() in a multithreaded program                            *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * When running a multithreaded program,                        *
  * delay may occur when multiple threads                        *
  * in a process issue poll requests                             *
  * concurrently.                                                *
  *                                                              *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  Poll processing builds Select Status Array (STAR), enqueues
  STAR on FuptStar chain and dequeues STAR once poll completes.
  Close processing from another thread scans FuptStar chain to
  find matching STAR and removes closing file descriptor from
  active PollFD. Process level FUPT latch is used to
  serialize STAR access among multiple threads in the process.
  Both poll processing and close processing obtain latch
  exclusive. When multiple threads concurrently process poll
  requests, some threads will have to wait for the latch. That
  can result in application delay.
  

Problem conclusion

• KEYWORDS: IDAAV7R5/K
  
  CONCLUSION:
  Change poll module BPXVSPE1 from three exclusive latch obtains
  to two shared and one exclusive.
  The first change from exclusive to shared was made for adding
  STAR to the head of the chain. Shared latch was used to
  serialize with close processing that obtained latch exclusive.
  Compare-and-swap logic was added to enqueue STARs.
  The second change was made for processing STAR output. Shared
  latch was used to serialize with close processing that obtained
  latch exclusive.
  

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:

  UJ05984 UJ05985 UJ05986

Modules/Macros

• BPXVSPE1 BPXVSSE2
  

Fix information

• Fixed component name

  OPENMVS SYS SRV

• Fixed component ID

  5695SCPX1

Applicable component levels

• R7B0 PSY UJ05984

     UP21/07/21 P F107 ¢

• R7C0 PSY UJ05985

     UP21/07/21 P F107 ¢

• R7D0 PSY UJ05986

     UP21/07/21 P F107 ¢

Fix is available

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