• Change any virtual machine's dispatch Friority
characteristics
and opera ting
For details on
see "Section 3. how many of these and other functions are accomplished,
CP Commands" in this publication.
Depending upon the system installation, the system operator may also
be the operator of a large OS or DOS batch processing system that is run
in the virtual machine environment. Another duty of the system operator
is to control the data traffic from re.ote work stations. Information
on V8/370 control of such data transfer is detailed in the Regardless of the real system resources and the tasks and procedures
used, syste.s are subject to hardware and prcgram malfunction. The
Interactive Problem Control System of V!/370 provides a method of
recording and maintaining a history of V!/370 and virtual machine program problems. The V!fl70 Guide provides tpe details on how to use this system. Problems that are a result of a hardware fault are usually detected by the hardware itself, and trigger the recording of register contents
and sense values (related to the occurrence of the error) in V8/370's error recording area.
Regardless of whether the malfunction origin is hardware or software,
the system operator (in most cases) is notified of the seriousness of
the situations" by means of console indicators/alar.s or by console
diagnostic messages. These all serve to inform the operator that: • The system operation can continue as before. • The system operation can continue with reduced power/resource. • System restart and recovery is co.mencing. • System operation is'terminated. The type of recovery that is attempted is described in "System/370 Recovery 8anagement Support", which follows. System/370 Recovery Management Support IE! System/370 atte.pts correction of most aachine errors without program assistance. CP is notified, via an interruption, of both
intermittent and per.anent machine errors to allow error recording and
recovery procedures to The following recovery features are implemented in the IB! Systea/370 hardware: • Retry of the failing processor operations • Validity checking on processor and control storage to correct all
single-bit errors • I/O operation retry facilities including an extended channel status vord (ECSlf), which provides channel retry data to channel and control
unit retry procedures • Expanded machine check interruption facilities tc improve error
recording and recovery procedures
2 V8/370 Operator's Guide

!!ACHINE CHECK HANDLER (!tCH) You can set the recording mode to record errors corrected by processor
retry (logically termed as CPU retry) and Error correction Code (ECC)
wi th the SET !tODE command,. In attached Frocesscr applica tions,
recording .ode can be set for either or both prccessors. For processor
retry, the default setting is record mode. !Qte: The SET !!ODE !!AIN command is invalid for 3031, 3032, and 3033 processors. When processor retry or ECC succeed in correcting errors, and the
processor 1S 1n record mode, the machine check handler records the
error. When processor retry or ECC fail, the machine check handler: • Attempts to isolate the failure to one page frame and makes that page
frame invalid or unavailable for paging. • Attempts to isolate the failure to one virtual machine and logs off
or resets that virtual machine. • Attempts to isolate the failure to portions of the system and to
continue system operation in degraded mode. • Abnormally terminates the system when recovery is not possible; or,
if V8/370 is operating in attached processor mode and the malfunction
is isolated to the attached processor and to a particular virtual
lIachine, then, system operation continues in uniprocessor Jlode,. MCH records an error whenever any of the following conditions occur: • Processor retry occurred'. • ECC corrected datal. • Hardware reported a buffer or DLAT (Data Look Aside Table) error. • Multiple-bit storage failure. • External da,age. • Storage protection feature damage. • Timer error. • System damage. • Instruction processor damage. CHANNEL CHECK HANDLER CCCH) Whenever a channel control check, channel data check, or interface
control check occurs, the channel check handler (CCH) constructs an
error record and records the results in an IOERBLOK. The error recovery
procedures use this IOERBLOK to retry the error. Recovery is not attempted for channel errors associated with virtual machine I/O events.
1 VM/370 records these errors only under specific conditions,. The
conditions for recording these errors are detailed in the !nd Section 1. Intro. to Operational Ctrl. of the VM/370 System 3