VM65696: SCHEDULER LOCK IMPROVEMENTS

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Poor system performance in large N-way partitions due to
  cache alignment of the scheduler lock and nearby fields.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All users of z/VM                            *
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  * PROBLEM DESCRIPTION:                                         *
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  * RECOMMENDATION: APPLY PTF                                    *
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  Customers might experience decreased performance due to
  the location of the scheduler lock (SRMSLOCK).  The allocation
  of the SRMBK provides no cache boundary alignment, so it is
  indeterminate exactly which other fields in the SRMBK will
  happen to be in the same cache line as SRMSLOCK.
  
  Interference from reads/writes to other data in the same cache
  line can reduce the efficiency with which the control program
  (CP) can manage the scheduler lock.
  

Problem conclusion

• The code which allocates the SRMBK is modified to allocate an
  entire page of memory for the SRMBK, thus assuring cache
  boundary alignment.  The scheduler lock (SRMSLOCK) is relocated
  to a new displacement within the SRMBK such that there are no
  other fields within the same cache line and thus no interference
  from accesses of those fields by other processors.
  
  Further, the SRMSLOCK is split so that the spin lock area
  (SYNBK) occupies the very end of a cache line, while the spin
  lock extension area (SYNBX) follows contiguously at the start
  of the next cache line.  This alignment maintains the
  requirement of these two sections being contiguous.  However,
  by being located in two separate cache lines, updates that
  spinning CPUs make to masks and statistics located in the SYNBX
  do not interfere with CPUs which are trying to update the SYNBK.
  

Temporary fix

• FOR RELEASE VM/ESA CP/ESA R630 :
  PREREQ: VM65586 VM65418 VM65419
  CO-REQ: NONE
  IF-REQ: NONE
  

Comments

APAR Information

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

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

  UM34572

Modules/Macros

• CBITABLE HCPAFF   HCPALF   HCPALL   HCPALR
  HCPAPJ   HCPCBI   HCPCFM   HCPCPA   HCPCPU   HCPCSA   HCPDSB
  HCPDSP   HCPHIP   HCPHRU   HCPHTF   HCPISR   HCPLGN   HCPLMC
  HCPMCI   HCPMCS   HCPMCW   HCPMOL   HCPMPC   HCPMPS   HCPMTF
  HCPMTO   HCPMTS   HCPPPI   HCPPTE   HCPPTF   HCPPTG   HCPQDO
  HCPRLG   HCPRLU   HCPSCI   HCPSCJ   HCPSGP   HCPSHI   HCPSNR
  HCPSRM   HCPSRMBK HCPSRN   HCPSSI   HCPSTK   HCPSTL   HCPSTM
  HCPSTP   HCPSXP   HCPTHQ   HCPWAI   HCPZPQ
  

Fix information

• Fixed component name

  VM CP

• Fixed component ID

  568411202

Applicable component levels

• R630 PSY UM34572

     UP15/03/24 P 1601

• R540 PSN

     UP

• R620 PSN

     UP

Fix is available

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