Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output command process
Reexamination Certificate
1999-02-10
2002-04-02
Shin, Christopher B. (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output command process
C710S017000, C710S036000, C710S120000
Reexamination Certificate
active
06366963
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to method and apparatus for processing input/output requests by connecting a host computer and an input/output control unit by a plurality of channel buses and, more particularly, method and apparatus for processing input/output requests by using channel buses of different transfer speeds.
FIG. 1
shows an example of an input/output (I/O) subsystem using magnetic tape apparatuses. The input/output subsystem is constructed by: a magnetic tape control unit
410
which functions as an input/output control unit; and a plurality of magnetic tape drive units
412
-
1
to
412
-
4
each of which functions as an input/output unit. Devices ID #
1
to #
4
are defined for the magnetic tape drive units
412
-
1
to
412
-
4
. The magnetic tape control unit
410
has, for example, two input/output (I/O) ports
420
-
1
and
420
-
2
. Port numbers (A) and (B) are defined for the I/O ports
420
-
1
and
420
-
2
. Channel units
416
-
1
and
416
-
2
of host computers
414
-
1
and
414
-
2
are connected to the I/O ports
420
-
1
and
420
-
2
through channel buses
418
-
1
and
418
-
2
. Channel numbers (A) and (B) are defined for the channel units
416
-
1
and
416
-
2
. In the following description, the above components are merely expressed as channels (A) and (B) and ports (A) and (B).
A processing operation for an input/output request from the host computer will now be briefly described. For example, it is now assumed that an input/output request such as a write request for a magnetic tape loaded in the magnetic tape drive unit
412
-
1
was generated by the host computer
414
-
1
. The channel (A) of the host computer
414
-
1
first generates a start I/O request (activation request) which designates a device machine No. #1 of the magnetic tape drive unit
412
-
1
to the I/O port (A). In response to the start I/O request from the port (A), the magnetic tape control unit
410
discriminates whether the port (B) has been coupled to the channel (B) or not. When the port (B) is not being coupled, the magnetic tape control unit
410
accepts the start I/O request for the port (A) and is coupled with the channel (A) and responds a normal end of the start I/O request and executes a transferring process of a command sequence.
When the start I/O request from the channel (A) is received by the port (A), if the channel (B) has been coupled, a busy response is returned. When the transferring process by the coupling of the channel (B) and the port (B) is finished, a status response of a unit end is performed from the port (B) to the channel (B) and they are disconnected. In association with the disconnection, a busy end indicative of a busy cancellation is also performed from the port (A) to the channel (A). An activation request is again performed from the channel (A) in the waiting state to the port (A) by the busy response.
In the input/output control unit for processing input/output requests from such a plurality of channels, it is necessary to equivalently execute services for the input/output request of each channel. However, in the case where transfer speeds of the channel buses differ, or a different transfer protocol is used in dependence on the channel, like an electric channel bus or an optical channel bus, there is a tendency such that the services are one-sided to the high speed channel by all means, so that there is a problem of reduction of the services to the low speed channel. As a system environment, in many cases, the high speed host computer and the low/middle speed host computer mixedly exist. Further, the high speed host computer and the middle/low speed host computer are connected so that they can be cross-called. In such a case, a problem similar to that mentioned above occurs. This point will now be described with reference to FIG.
1
. For instance, it is now assumed that the channel (A) is a low speed channel and the channel (B) is a high speed channel. An input/output control in this case is executed as shown in, for example, a time chart of FIG.
2
.
When a start I/O request
500
is sent from the high speed channel (B) to the port (B) and a coupling completion response
502
by the normal end is obtained, transferring processes
504
and
506
of a command sequence between the high speed channel (B) and the port (B) are executed. Now, assuming that a start I/O port request
508
is generated from the low speed channel (A) to the port (A) for periods of time of the transferring processes
504
and
506
, since the port (B) has been coupled, a busy response
510
is returned. After completion of the transferring process
506
, a unit end
512
is returned from the port (B) to the high speed channel (B) and the coupling is disconnected. In association with the unit end
512
, a busy end
514
indicative of the busy cancellation is subsequently returned from the port (A) to the low speed channel (A) in the waiting state of the busy cancellation. When it is now assumed that the next input/output request has been generated from the high speed channel (B) which received the unit end
512
, a start I/O request
516
as an activation request is immediately outputted from the high speed channel (B) to the port (B). After a coupling completion response
518
was performed, transferring processes
520
and
522
are again executed. On the other hand, the low speed channel (A) which received the busy end
514
recognizes the busy cancellation and generates a start I/O request
524
to the port (A). However, it takes a time until the start I/O request
524
is received by the port (A) after the busy end
514
was outputted. For such a period of time, the port (B) has been coupled by the start I/O request
516
from the high speed channel (B). Therefore, for the start I/O request
524
from the low speed channel (A), a busy response
526
is again outputted from the port (A) and the low speed channel (A) again waits for a busy cancellation. Therefore, so long as the input/output request is continuously performed to the high speed channel (B), a loop process of the start I/O request, busy response, and busy end is repeated for the low speed channel (A). The input/output request is not accepted and the services deteriorate. In the worst case, since such a loop process is executed for a long time, there is a problem of the occurrence of a check condition such that the host computer of the low speed channel (A) judges that some abnormality occurred in the channel unit or input/output subsystem. In dependence on a control method, when the input/output request from the high speed channel is continuously performed, there is also no time to respond to the busy end in association with the end of the coupling on the high speed channel side for the low speed channel (A). In such a case, the low speed channel in the busy cancellation waiting state cannot obtain the busy end even if it waits for the busy cancellation for a long time. A situation such that the busy cancellation waiting times out and the input/output request of the low speed channel is finished as an error occurs. As a method of solving the above problem such that the services of the input/output control apparatus are one-sided to a specific channel as mentioned above, there is a method of time-divisionally changing the priority of the route so that the services are equivalently given to each input/output port.
FIG. 3
shows the case where eight channels of ports (A to H) are provided for the input/output control unit. Priorities are sequentially allocated to the ports (A to H) by clocks in accordance with that order. It is now assumed that, for example, there are activation requests to all of the input/output ports (A to H) at time to. In this instance, there is a clock in a slot of the I/O port (C), the priority is set, and the coupling at the I/O port (C) is accepted. With respect to the other I/O ports, the busy response is automatically reported. Now, assuming that there are two activation requests of the I/O ports (B and E) at time t
0
, the coupling of the
Fujitsu Limited
Greer Burns & Crain Ltd.
Shin Christopher B.
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