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.
|SYSTEM NAME||The name of the system attached to the coupling facility (from IEASYSxx Parmlib member,
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
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.
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.|
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.
Unknown operation mode:
|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:
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.|