A fix is available
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 number
OA61558
Reported component name
OPENMVS SYS SRV
Reported component ID
5695SCPX1
Reported release
7B0
Status
CLOSED PER
PE
NoPE
HIPER
YesHIPER
Special Attention
NoSpecatt / Xsystem
Submitted date
2021-06-01
Closed date
2021-07-07
Last modified date
2021-11-16
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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[{"Business Unit":{"code":"BU054","label":"Systems w\/TPS"},"Product":{"code":"SG19M"},"Platform":[{"code":"PF054","label":"z\/OS"}],"Version":"7B0"}]
Document Information
Modified date:
17 November 2021