Abstract: A large data processing system includes a channel path management program that is periodically executed during operation of the system to gather control unit and subchannel utilization statistics and to monitor such statistics. If the degree of utilization of a channel path or an I/O device exceeds a predetermined threshold value, one or more change(s) is(are) dynamically made in the channel path configuration.

Abstract: In a computer I/O system including a plurality of link-level facilities and a dynamic switch having a plurality of ports, each link-level facility being attached to an individual one of the ports, a mechanism and method for assigning a unique link level address to each of the link-level facilities. As each of the link-level facilities comes on line, it sends an acquire link address (ALA) frame and waits for a response (ACK) frame. The ALA frame may be addressed to a general to-whom-it-may-concern address and have a source address of who-am-I. Only a dynamic switch normally assigns link addresses. When receiving an ALA frame, the dynamic switch returns an ACK frame having a unique link address assigned to the sender of the ALA frame. Provision is made for determining if there is a dynamic switch present, or, if the link-level facilities are connected together by a static connection through the dynamic switch, for the link-level facility of a channel to assign the unique link addresses.

Abstract: The disclosure provides a unique multiprocessing (MP) method for executing on plural CPUs of the MP a uniprocessor system (UPS) program not written to run on a MP system. Separate copies of the UPS are provided in the shared main storage (MS) of the MP. A hypervisor type of control program (called a partitioned multiprocessing system, PMP) uses the MP method to enable simultaneous execution of the plural copies of a UPS on different CPUs of the MP as UPS guest virtual machines. PMP can dedicate any CPU to the sole execution of a particular copy of UPS. The copies of the UPS run on the different CPUs independently of each other, but they may share I/O devices.

Abstract: For a CPU I/O request, the disclosed methods find a physical channel path within a logical channel (LCH) likely to be connectable to a requested device by using channel path count (CAT count) fields. The CAT counts respectively indicate the current number of uncompleted requests accepted by the respective physical channels in the data processing system. An available physical channel in the LCH with the smallest CAT count is found as the candidate channel path for a connection attempt to the requested device. If the lowest CAT count is equal for plural available channel paths, any of these plural channel paths may be selected as the candidate channel path. The CAT count for a channel path is incremented for each successful connection of any device to that channel path. The CAT count for a channel path is decremented upon receiving a signal indicating that a successfully connected I/O device has completed the operation for a request.