Subchannel Activity section

This section contains a summary line for each system attached to the coupling facility. MVS treats the set of available subchannels for a coupling facility as a pool of resources for any request to that facility. Therefore, the subchannel activity data is not reported by individual subchannel. MVS handles the load balancing across the subchannels automatically.

Figure 1. Coupling Facility Activity Report - Subchannel Activity

                                  C O U P L I N G   F A C I L I T Y   A C T I V I T Y

     z/OS V2R4              SYSPLEX UTCPLXJ8            DATE 05/11/2019            INTERVAL 030.00.000
                            RPT VERSION V2R4 RMF        TIME 13.00.00              CYCLE 01.000 SECONDS

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 COUPLING FACILITY NAME = CX7CFP87
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                                                    SUBCHANNEL  ACTIVITY
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          # REQ                          ----------- REQUESTS -----------   ------------------ DELAYED REQUESTS --------------
 SYSTEM   TOTAL   -- CF LINKS --  PTH             #   -SERVICE TIME(MIC)-              #     % OF  ------ AVG TIME(MIC) ------
 NAME     AVG/SEC TYPE  GEN  USE  BUSY            REQ     AVG    STD_DEV               REQ    REQ   /DEL    STD_DEV     /ALL

 R7D        3599K CIB     4    4     0   SYNC      3301K   23.5       9.7   LIST/CACHE    0   0.0    0.0        0.0      0.0
          1999.5  SUBCH  28   28         ASYNC   236454    84.1     139.7   LOCK          0   0.0    0.0        0.0      0.0
                                         CHANGED      0  INCLUDED IN ASYNC  TOTAL         0   0.0
                                         UNSUCC       0     0.0       0.0
 R70      436212K ICP     4    4  3482   SYNC    435637K    5.2       3.6   LIST/CACHE   18K  0.0  285.0      215.6      0.0
          242340  SUBCH  28   28         ASYNC   141411    70.9     152.5   LOCK          0   0.0    0.0        0.0      0.0
                                         CHANGED  17622  INCLUDED IN ASYNC  TOTAL        18K  0.0
                                         UNSUCC       0     0.0       0.0

…

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                                                       CHANNEL PATH DETAILS
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 SYSTEM NAME  ID  TYPE   OPERATION MODE      DEGRADED   DISTANCE    PCHID    AID      PORT   ------- IOP IDS -------

 R7D          C4  CIB    1X  IFB  HCA3-O LR     N             <1     704    000D        01   06
              C5  CIB    1X  IFB  HCA3-O LR     N             <1     705    000D        01   06
              C6  CIB    1X  IFB  HCA2-O LR     N             <1     706    000C        02   05
              C7  CIB    1X  IFB  HCA2-O LR     N             <1     707    000C        02   05

Table 1. Fields in the Coupling Facility Activity Report - Subchannel Activity
Field Heading	Meaning
SYSTEM NAME	The name of the system attached to the coupling facility (from IEASYSxx Parmlib member, SYSNAME parameter). The name is preceded by an '*' if the data for this system is incomplete for this interval, for example because the gatherer has been stopped.
# REQ TOTAL # REQ AVG/SEC	TOTAL Total number of requests to this facility. This number will usually be greater than the sum of the individual structure values from the previous report section because it includes global coupling facility commands that are not attributable to any structure. AVG/SEC Average number of requests per second for this facility. This field can be used as a quick way of determining which systems are generating the most activity for a given facility which in turn indicates where to focus tuning or load balancing efforts.
CF LINKS	TYPE Channel path type. GEN Number of subchannels that are defined. USE Number of subchannels MVS is currently using for coupling facility requests.
PTH BUSY	Path busy - the number of times a coupling facility request was rejected because all paths to the coupling facility were busy. A high count combined with elongated service times for requests indicates a capacity constraint in the coupling facility. If coupling facility channels are being shared among PR/SM partitions, the contention could be coming from a remote partition. Identifying path contention: There can be path contention even when this count is low. In fact, in a non-PR/SM environment where the subchannels are properly configured, the total number of delayed requests, and not PTH BUSY, is the indicator for path contention. If this value is high, it means MVS is delaying the coupling facility requests and in effect gating the workload before it reaches the physical paths. Before concluding you have a capacity problem, however, be sure to check that the correct number of subchannels are defined in the I/O gen. PR/SM environment only: If coupling facility channels are being shared among PR/SM partitions, PTH BUSY behaves differently. You potentially have many MVS subchannels mapped to only a few coupling facility command buffers. You could have a case where the subchannels were properly configured (or even under-configured), subchannel busy is low, but path busy is high. This means the contention is due to activity from a remote partition.
REQUESTS - The requests are shown in four categories.
# REQ SYNC	Number of synchronous requests from this system to the coupling facility.
# REQ ASYNC	Number of asynchronous requests from this system to the coupling facility. This number includes requests that might have started out as synchronous requests but were converted to asynchronous requests due to lack of subchannel or due to the heuristic setting.
# REQ CHANGED	Number of requests from this system that were changed from synchronous to asynchronous due to lack of subchannel. This value is a subset of # REQ ASYNC value.
# REQ UNSUCC	Number of requests which could not be completed due to hardware problems. This number should normally be zero. If it is non-zero, there is a hardware problem that needs to be investigated. The reason it is reported here is to judge to what impact extent hardware problem(s) impact coupling facility performance.
SERVICE TIME - AVG SERVICE TIME - STD_DEV	The average service time in microseconds and the standard deviation of the service time spent for requests to the coupling facility. The average service time in conjunction with its standard deviation can be used to determine potential impacts to the end user. Even though the average service time is low the standard deviation can be high indicating a wide fluctuation. This category is for the request types SYNC, ASYNC, and UNSUCC, the fields are not applicable for column CHANGED.
DELAYED REQUESTS - These columns lists possible contention reasons for requests sent to the coupling facility.
# REQ LIST/CACHE	Number of delayed requests across all LIST and CACHE structures.
# REQ LOCK	Number of delayed requests across all LOCK structures.
# REQ TOTAL	Number of delayed requests across all structures.
% OF REQ	The percentage of requests delayed, related to the number of List/Cache requests, Lock requests and total requests.
AVG TIME - /DEL	The average delay time in microseconds over all delayed requests.
AVG TIME - STD_DEV	The standard deviation to the average delay time.
AVG TIME - /ALL	The average delay time in microseconds over all requests, whether delayed or not.

Table 2. Fields in the Coupling Facility Activity Report - Subchannel Activity - Channel Path Details
Field Heading	Meaning
Note: If the hardware cannot provide values for a measurement, the field remains blank.
SYSTEM NAME	The name of the system attached to the coupling facility (from IEASYSxx Parmlib member, SYSNAME parameter).
ID	The hexadecimal identifier of a channel path (CHPID) that is connected to the coupling facility.
TYPE	Channel path type.
OPERATION MODE	Channel path operation mode. It describes the data rate, bandwidth, protocol, and adapter type of the channel path. A data rate of, for example, 1GBIT denotes a rate of 1.0625 gigabit per second. A bandwidth of, for example, 12X denotes a twelve-fold bandwidth. Protocols: IFB – InFiniBand IFB3 – InFiniBand 3 CEE – Converged Enhanced Ethernet GEN3 – PCIe third generation protocol Adapter types: HCA2-O – Host Channel Adapter2-optical HCA2-O LR – Host Channel Adapter2-optical long reach HCA3-O – Host Channel Adapter3-optical HCA3-O LR – Host Channel Adapter3-optical long reach PCIE-O SR – Peripheral Component Interconnect Express short reach ROCE LR – RDMA over Converged Ethernet long reach Unknown operation mode: UNKNOWN
DEGRADED	Character Y in this column indicates that the channel path is operating at reduced capacity (degraded) or not operating at all.
DISTANCE	Estimated distance in kilometers. The value is calculated as follows: `Average round-trip path time in microseconds ---------------------------------------------- 10 microseconds / kilometer` A value of zero means that the time was not measured.
CHID	Physical channel identifier.
AID	The hexadecimal coupling adapter identifier associated with the channel path.
PORT	The hexadecimal port associated with the channel path.
IOP IDS	The hexadecimal identifiers of I/O processors (System Assist Processors) to which the channel path is accessible.