z/VM: CP Commands and Utilities Reference - z/VM - IBM

SET SRM
1394 z/VM: CP Commands and Utilities Reference
18 openings are available to E3 users, but none of the openings is guaranteed
against occupation by E1 and E2 users. When E1 and E2 users do occupy
these openings, you can expect them to get out of the way relatively quickly
compared with the time scale of an E3 transaction.
DSPBuf INITial
sets the parameters back to their initial values which, for practical purposes, are
infinity.
MAXWSS storpct[%]
sets the maximum working set that any normal user is allowed to have. It is
specified as a percentage of the system’s pageable storage. (Pageable storage
is also known as the dynamic paging area, DPA, or paging pool.) If a user’s
working set size (WSS) grows and exceeds this specified percentage of the
pageable storage, the user is dropped from the dispatch list and put back in the
eligible list.
When a user is put in the eligible list for exceeding the MAXWSS, that user is
treated as though his or her stay in the dispatch list had run to completion. The
user is advanced to the next user class (for example, Q3) and is placed well out
in the eligible list so that he or she does not immediately get back into the
dispatch list to run again. The intent is to delay the user for a while to prevent
him or her from occupying any more pages than he or she already does: the
installation has told the scheduler (through the MAXWSS setting) that a user
requires a working set size too large to be run. (For example, the installation
does not want such large WSS users competing with the normal, more
interactive, workload.) Still, the user travels through the eligible list and gets
another chance to run, although it is likely that all of this user’s page frames
will, in the meantime, have been stolen and given to other users. When the
user does get to run again, the scheduler again evaluates the working set size:
a user with too great a working set size (WSS) requirement gets to run only
briefly before the MAXWSS mechanism removes him or her from the dispatch
list again.
For all this to work as intended, the system must have an actual eligible
list—that is, the scheduler must consider the system to be storage constrained
according to the setting of the SET SRM STORBUF parameters.
If the MAXWSS percentage is set larger than the STORBUF percentages, the
STORBUF percentages take precedence. A user is dropped from the dispatch
list and sent to the eligible list if his or her WSS grows so large that it exceeds
the STORBUF percentage for that user’s class. When this happens, users
never get a chance to grow large enough to reach the MAXWSS percentage.
Effectively, the MAXWSS control is inoperative when it is set larger than the
STORBUF percentages. The value specified for MAXWSS may range up to
9999%.
Users having absolute shares are given special consideration. If a user’s
absolute share is larger than the MAXWSS percentage, the user is allowed to
grow beyond the MAXWSS percentage and to become as large as his or her
absolute share percentage. However, such users are still limited by the
STORBUF percentage. Having a large absolute share allows a user to exceed
the MAXWSS control but not the STORBUF control.
The MAXWSS control does not affect Q0 users, such as users with the
QUICKDSP attribute.