MRSYTCPMPrologControl Block Contents Storage Layout Cross Reference MRSYTCPM Prolog
DSECT NAME - SYTCPM
FUNCTION - Map a Monitor record.
LOCATED BY -
Through the Monitor Control Area
REFERENCED CONTROL BLOCKS -
MRRECHDR Monitor Record Header
NAME - MRSYTCPM
DESCRIPTIVE NAME - Monitor Sample Record
Domain 0 - System Domain
Record 18 - Channel Path Measurement Data
DESCRIPTION - Provide utilization data for each channel path.
NOTES:
- This record is generated only when the Channel-Path
Measurement Facility (without extended channel
measurements) is installed on the system.
If the Channel-Path Measurement Facility with
extended channel measurements is installed, then
the MRSYTEPM Monitor record (Domain 0, Record 20)
will be generated instead of this one.
- When VM is running native, this record will be
generated only when the Channel-Path Measurement
Facility (without extended channel measurements)
in installed on the system.
- When VM is running in an LPAR in Multiple Image Facility
mode, physical channel paths may be shared with other
partitions. The data provided in this record represents
channel utilization attributable to the logical partition
in which VM is running.
- When VM is running second level, the Channel-Path
Measurement Facility is not installed. Thus this
record will not be generated.
- SYTCPM_CALOFFST should always be used to locate the
SYTCPM_DATA area.
- A SYTCPM_CHPATH entry contains valid data only when its
SYTCPM_INVALID bit is OFF.
- Each channel path entry is constructed independently, on a
schedule chosen by the channel subsystem (CSS), rather than
at the monitor sample interval. Thus, the analysis program
must look at the timestamp and busy time in *each* channel
path entry, subtract from them the corresponding values in
the previous record, and then divide to get the busy time
as a fraction of the interval between the two samplings
*by the CSS* of that channel path's statistics. Two
consequences of this extra "layer" of sampling are:
1) Reducing the monitor sample interval will not necessarily
give finer-grained statistics for channel path usage.
2) Depending on when the monitor samples occur with respect
to the channel subsystem's samples, the intervals between
successive records may vary substantially. For example,
if the channel subsystem samples every 5 seconds and monitor
writes a sample record every 8 seconds, then on average,
three out of five times, the difference between monitor
records will represent 5 seconds of channel-path activity,
and the other two out of five times, the difference will
represent 10 seconds of activity.
Finally, note that the timestamp and busy time for a given
channel path might be identical to that in the previous
record, if the CSS has not updated the information in the
interval. In this case, there is effectively no interval
reported on between this pair of records, a later record
with a different timestamp must be used to compute usage
for the channel path.
- If the SYTCPM_INVALID bit is OFF but the SYTCPM_INIT bit is
ON in a SYTCPM_CHPATH entry, then the entry represents the
start of a new reporting "epoch" for the channel path. A
discontinuity in the timer values may have occurred since
the sample in the previous SYTCPM record. That is, the
timestamp and busy time in this entry are valid, but are not
related to the corresponding values in the previous monitor
record. The values in this record can only be used as a
starting point for the interval between this record and the
one after it. No information can be deduced about the
activity during the period between the time of the previous
record's sample for this channel path and that of this
record's sample.
The first valid SYTCPM_CHPATH entry recorded for each
channel path will always have SYTCPM_INIT on, as will any
entry which follows one or more entries with SYTCPM_INVALID
ON (for the same channel path). It is also possible for
SYTCPM_INIT to appear in an entry even when no preceding
entry for the channel path shows SYTCPM_INVALID.
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