EP0267464A2
Expired / Lapsed
EP
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Method for controlling processor access to input/output devices
Assignee: International Business Machines Corp
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Filing: 1987-10-20
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Granted: —
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Expires: 2007-10-20
Abstract
Abstract A method for controlling processor access to input/output control units and devices devices connected to the control units to prevent control unit and device lockout due to the condition where the channel turn-around time becomes less than the device controller's housekeeping time is disclosed. The problem of control unit and device lockout is overcome by monitoring path and device activity for a given processor while at the same time keeping track of other processors waiting for a given path and device. When it is determined that a given number of consecutive input/output operations have been accomplished for a given processor and at the same time another processor requires this resource, then a busy condition will be asserted for new input/output requests from the current processor for the currently accessed path and/or device. This action forces the offending processor to wait until the controller and/or the device is again available.
Inventors
- 👤 Fred Poole
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-29 08:11
CPC Classifications
G; G06; G06F; G06F13/00; G06F13/14
Claims Analysis
Total Claims: 10
Claim 1
Independent Claim
205 words
A method for controlling processor access to input/output control units and devices connected to the control units for each channel input/output request in a shared device multi-processor system comprising for each new input/output request by a processor the steps of testing for contention of a control unit requested by a processor, and if contention exists for the control unit, determining if a predetermined number of accesses have been made by a current processor having access to the control unit; if a predetermined number of accesses have been made by a current processor having access to the control unit for which there is contention by another processor, signalling the current processor with a busy status to allow access by another processor to the control unit; testing for contention of a device connected to the control unit, and if there is contention determining if a predetermined number of consecutive input/output operations have been performed by a current processor having access to the device; and if a predetermined number of consecutive input/output operations have been performed by the current processor on the device for which there is contention by another processor, signalling the current processor with a busy status to allow access by another processor to the device.
Claim 2
Independent Claim
205 words
A method for controlling processor access to input/output control units and devices connected to the control units for each channel input/output request in a shared device multi-processor system comprising for each new input/output request by a processor the steps of testing for contention of a control unit requested by a processor, and if contention exists for the control unit, determining if a predetermined number of accesses have been made by a current processor having access to the control unit; if a predetermined number of accesses have been made by a current processor having access to the control unit for which there is contention by another processor, signalling the current processor with a busy status to allow access by another processor to the control unit; testing for contention of a device connected to the control unit, and if there is contention determining if a predetermined number of consecutive input/output operations have been performed by a current processor having access to the device; and if a predetermined number of consecutive input/output operations have been performed by the current processor on the device for which there is contention by another processor, signalling the current processor with a busy status to allow access by another processor to the device.
Claim 3
Dependent Claim
75 words
The method according to claim 1, wherein the step of testing for contention of a control unit comprises the steps of: determining for each channel input/output request if there are other channels which are requesting access to the same device; determining if a current channel request is from a same channel as a last request; counting consecutive accesses by a current channel to an input/output device; and testing said count against a predetermined threshold value.
Claim 4
Dependent Claim
105 words
The method according to claim 1, wherein each control unit includes a plurality of paths for allowing access to a plurality of devices connected to the control unit and the step of testing for contention of a control unit comprises the steps of: determining for each channel input/output request if there are other channels which are requesting access to the same path of a control unit; determining if a current channel request is from a same channel as a last request; counting the number of path accesses by the current processor having access to the path; and testing said count against a predetermined threshold value.
Claim 5
Dependent Claim
196 words
The method according to claim 1, wherein each control unit includes a plurality of paths for allowing access to a plurality of devices connected to the control unit and the step of testing for contention of a control unit comprises the steps of: determining for each channel input/output request if there are other channels which are requesting access to the same path of a control unit; determining if a current channel request for a path of control unit is from a same channel as a last request; counting the number of path accesses by the current processor having access to the path; and testing the count of the number of path accesses against a predetermined threshold value; and wherein the step of testing for contention of a control unit comprises the steps of: determining for each channel input/output request if there are other channels which are requesting access to the same device; determining if a current channel request for a device is from a same channel as a last request; counting consecutive accesses by a current channel to an input/output device; and testing the count of the number of consecutive accesses against a predetermined threshold value.
Claim 6
Dependent Claim
56 words
The method according to claim 4, wherein if the current channel request for a path in the control unit is not equal to the last path, further comprising the steps of: setting the current path equal to the last path; resetting the path usage count; and saving the path usage count and the last path argument.
Claim 7
Dependent Claim
38 words
The method according to claim 4, wherein if the number of path accesses by the current processor has not exceeded said predetermined value, further comprising the step of saving the path usage count and the last path argument.
Claim 8
Dependent Claim
38 words
The method according to claim 4, further comprising, after the step of signalling, the steps of: resetting the last path serviced argument; resetting the device and path usage count; and saving said count and the last path argument.
Claim 9
Dependent Claim
60 words
The method according to claim 4, wherein if a device is requested by a channel input/output request is not requested on the same path as a last request for the device, further comprising the steps of: setting the current path as the last path; resetting the device and path usage count; and saving said count and the last path argument.
Claim 10
Dependent Claim
50 words
The method according to claim 4, wherein if for channel input/output request for a device the number of consecutive accesses by a current channel to the device has not exceeded said threshold value, then further comprising the step of saving the count of said number and the last path argument.
References Cited (Backward Citations)
No citation records indexed.
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