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Method and structure for switching multiple contexts in storage subsystem target device
| Details |
Inventors: Born, Richard M.; Ellis, Jackson L.; Springberg, David M.; Noeldner, David R.; Weston-Lewis, Graeme M.;
Assignee: LSI Logic Corporation (Milpitas, CA)
Primary Examiner: Lee; Thomas C.
Assistant Examiner: Perveen; Rehana
Attorney, Agent or Firm:
A storage target device controller (such as an embedded controller in a SCSI disk drive) processes multiple commands concurrently in accordance with the methods and structures of the present invention. Each command is stored within its own context within the target device controller to retain all unique parameters required for the processing of each command. Processing of multiple commands permits switching of command contexts within the target device to improve utilization of resources associated with the target device. For example, when a first, active, command context is prevented from further processing due to the status of the disk channel, an inactive command context may be swapped with the active command context to better utilize the host channel communication bandwidth. Similarly, a first active command context may be configured to automatically switch to a linked command context upon completion of processing to further ease management of multiple contexts. In a preferred embodiment of the present invention, a set of registers contain the active context while a second set of registers contains an inactive command context. The sets of registers are configured in such a way that the active and inactive context may be rapidly switched with no intervention by the microprocessor. The inactive register set may be read or written directly by the microprocessor, or may be automatically loaded/stored from/to a buffer memory in the target device by shifting a predetermined context structure into the inactive register set through an interface pad with the buffer memory. |
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DETAILED DESCRIPTION The present invention solves the above and other problems, thereby advancing the state of the useful arts, by providing methods and associated structure to permit operation of multiple contexts within a target device.
Though the disk channel may prevent the target from operating upon other commands which require interaction with the actuator, a wide variety of other commands could be processed by the target device in accordance with the present invention.
Each command being processed by a target device is referred to herein as a context.
The methods of the present invention provide for storage within the target device of multiple contexts.
One command may be in process within a first context while other commands may be simultaneously serviced within other contexts of the target device.
Use of multiple contexts in accordance with the present invention allows processing of multiple commands with the target device to thereby better utilize the available bandwidth of the host channel and to reduce latency in servicing queued commands on initiator devices.
For a disk device, exemplary commands which may be processed in another context without requiring use of the disk channel are: read commands satisfied from a local cache, write caching, and non-data oriented commands and status (e.
g.
, SCSI sense, inquiry, and status).
The methods and structure of the present invention provide for rapid switching between multiple contexts that both require the disk channel to enable faster "back-to-back" (also referred to as coalesced) command processing.
A first command may be in process utilizing the disk channel while another command requiring the disk channel may be ready within the target device in a separate context.
When the first context (command) completes, the second context is automatically switched into an active state to begin processing of the second command context.
Such automatic switching within the target device permits coalesced disk read or disk write operations to be processed without incurring penalties inherent in the rotational latency of the rotating disk storage medium
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I/O Systems 
