THE DIAGNOSE INTERFACE
The diagnose interface, by use of the DIAGNOSE instruction, permits
operating systems running in virtual aachines under VM/310 to
communicate easily and efficiently with VM/310. While this topic provides a summary of the diagnose interface
functions, details about how to use the DIAGNOSE instruction to request
these functions are in the !!LJIQ By inserting DIAGNOSE instructions where appropriate in the operating system's code, the following functions can be requested by a virtual machine: Diagnose
Code • Examine the processor's extended identification code. -----0-- • Examine the contents of real storage. 4 • Invoke a virtual console function (that is, a CP command) 8 from the virtual machine operating system. • Obtain, from CP's pseudo timer: C
- Today's date (aa/dd/yy) - The time-of-day (hh:mm:ss) - Virtual and total processor time used by the virtual
machine • Release pages of virtual storage (but not discontiguous 10 storage) • Manipulate an input spool file in one of the following 14
ways:
- Read the next reader, punch, or printer spool data
- Select a new file for processing
- Repeat the active file n times - Restart the current file at the beginning
- Backspace one record
- Retrieve the subsequent file descriptor • Perform a standard DASD I/O operation. 18 • Clear the VM/310 I/O error recording area on disk. 1C • Perform a general I/O operation for tape or disk. 20 • Interrogate CP's device type and features control blocks. 24 • Notify CP that a dynamically modified channel program is to
be executed. 28 • Locate the start DASD address of the I/O error 2C
recording area (LOGREC). • Read one page of LOGREC data. 30 • Read the VM/310 system dump spool file. 34 10 IBM VM/370 Operating Systems in a Virtual Machine

• Read the VM/370 system symbol 38 • Dynamically update the VM/370 directory. 3C • Generate accounting cards for the user. 4C • Save the 3704/3705 Communications controller program in 50 page image format. • Specify that the 3270's PA2 key is to be used for either: 54
- Simulating an external interruption to a virtual machine,
such as VS lPL. - Clearing the output display of a 3270 screen. • Display the number of characters, up to the size of the 58
output area, on a display screen in one write operation. • Edit error messages. 5C • Determine the virtual machine storage size. 60 • Find, load, or purge a named segment. 64
--or--
Release discontiguous storage. • Invoke the virtual machine communication facility. 68 • Load a specific 3800 named system into a virtual 74
machine.
--or-- Save a storage image in a specific 3800 named
system. • Communicate between a virtual machine and VM/370 for MSS support. • Update fields in an online directory entry without
recompiling the directory. PAGE WAITS 78
84
If, during its execution, an OS- or DOS-created task or program must
wait for a VM/370 service such as a virtual storage page, VM/370 marks
the virtual machine nondispatchable even though other partitions or
tasks in that virtual machine may be ready and available for processing.
Those other tasks in the virtual machine cannot be dispatched by the
operating system until the VM/370 page wait is satisfied. Thus, the
highest priority program of the virtual machine gets almost all of the
Frocessor time allocated to that virtual machine, if it can use the time. Therefore, programs running in the other partitions experience
significant degradation. When multiFrogramming systems must be executed in a virtual machine,
.ake the partitions or regions as large as practical and execute all
jobs V=R. Also, consider using the VM/370 virtual =real option, reserved
page frames, or locked pages. When using the VM/370 virtual=real
oFticn, it eliminates paging for one virtual machine, but this may adversely affect the paging performance of other virtual machines. The
reserved Fage frames option tends to keep the most active pages in
storage, and the locked pages option locks the specified pages in
storage. Section 1. General Considerations 11