IOP contention

If the ASYNC service times exceed the guidelines, one possible cause could be a delay in the IOP microcode. The IOP (or SAP) handles I/O to DASD, CTC traffic and ASYNC CF requests prior to HiPerLinks. Any one of these could encounter a delay in the IOP, which in turn would delay the others.

To determine if this delay is occurring, look at the RMF™ I/O Queuing Activity report. The AVG Q LNGTH records only I/O and CTC requests, but a queue length greater than 1.0 suggests delays are occurring and should be investigated. In Figure 1, for example, the large AVG Q LNGTH of 7.58 was due to a Director Port busy condition.

Figure 1. Example: RMF CF Subchannel Activity Report

                        I/O   Q U E U I N G   A C T I V I T Y

          MVS/ESA                  SYSTEM ID J80
          SP5.1.0                  RPT VERSION 5.1.0
TOTAL SAMPLES =  7200    IOP   ACTIVITY RATE  AVG Q LNGTH
                          00      406.534        7.58

                 DELAY   % ALL
LCU  CONTENTION    Q    CH PATH  CHAN    CHPID    % DP   % CU
        RATE     LNGTH   BUSY    PATHS   TAKEN    BUSY   BUSY
000C     4.176    0.02    0.06    29     1.895   73.33   0.32
                                  35     1.870   73.75   0.15
000F    65.181   23.10    0.06    29    12.203   67.32   2.49
                                  35    12.240   60.11   3.87