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

SET SRM
1392 z/VM: CP Commands and Utilities Reference
In each case, the STORBUF values must be decimal numbers from 0 through
999, and aaa ≥ bbb ≥ ccc. Any value over 100 is an overcommitment of
storage.
Q0 users are left out of the above discussion to keep it simple. In fact, Q0
users are allowed to crowd into storage without limit. In effect then, all of
storage above the aaa percentage can be regarded as a buffer reserved for Q0
users. (Q0 users should not take too much of it, because this unspecified buffer
also serves to hold the pages of active users who are temporarily “dormant”
[between transactions].)
Although Q3 users may occupy the percentage of storage represented by ccc,
they do not have exclusive rights to it. This storage can be occupied by Q0, Q1,
Q2, and Q3 users, depending on which classes are generating a demand for it.
But the Q1 and Q2 buffers tend to eliminate some of the Q1 and Q2 demand,
so the ccc storage tends to be occupied mainly by Q3 users. Also, after a Q3
user gets in, he or she stays there for a relatively long time, and this gives the
Q3 users something of an advantage over other users when it comes to ccc
storage.
Similarly the Q2 users do not have exclusive rights to the buffer represented by
the difference bbb−ccc. This storage can be occupied by Q0, Q1, and Q2,
depending on which classes are generating a demand for it. But for the most
part it is occupied by Q2 users, just as the ccc storage is occupied mostly by
Q3 users.
The Q1 users do not have exclusive rights to the buffer represented by the
difference aaa−bbb. Both Q0 and Q1 users may occupy it.
STORBuf INITial
sets the percentage parameters back to their initial values, 125%, 105%, and
95%.
LDUBuf {ddd[%] eee[% ] fff[%]}
partitions the commitment of the system’s paging resources when the scheduler
chooses users to move from the eligible list to the dispatch list. The result is a
paging capacity buffering mechanism based on the transaction class of a user.
(See the description of the STORBUF parameter on page 1391 for a definition
of transaction classes.)
During system initialization, the number of paging DASD exposures is
determined. Users expected to have high paging rates in the dispatch list are
termed “loading users.” They are identified by recent DASD paging activity or
with the knowledge that their working sets have been moved to DASD since
they last ran. One loading user is regarded as keeping one paging exposure
busy. The LDUBUF (loading user buffer) percentages, then, determine the
number of loading users allowed in the dispatch list by transaction class.
The SET SRM LDUBUF parameters partition the paging capacity as follows:
ddd[%]
is the percentage of paging exposures the scheduler is to view when
considering adding a loading E1, E2, or E3 user to the dispatch list. If
the total number of loading users currently in the dispatch list plus the
loading En user under consideration exceeds the ddd percentage of
paging exposures, the user may not be added immediately and is
delayed further.