Dequeuing from a host adapter two-dimensional queue

Details Dequeuing from a host adapter two-dimensional queue Dequeuing from a host adapter two-dimensional queue

2003-05-21

2004-09-07

Gaffin, Jeffrey (Department: 2182)

Electrical computers and digital data processing systems: input/

Input/output data processing

Input/output command process

C710S038000, C710S052000, C710S112000, C712S225000

Reexamination Certificate

active

06789134

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to host adapters that interface two I/O buses, and more particularly, to dequeuing blocks from queues for host adapters.
2. Description of Related Art
Hardware control blocks, sometimes called sequencer control blocks, or SCSI command blocks (SCBs), are typically used for transferring information between a software host adapter device driver in a host computer system
106
and a host adapter integrated circuit
120
that controls operations of one or more peripheral devices. Those of skill in the art know methods for queuing SCBs.
For example, see copending and commonly assigned U.S. patent application Ser. No. 07/964,532 entitled “Intelligent SCSI Bus Host Adapter Integrated Circuit,” of Craig A. Stuber et al. filed on Oct. 16, 1992, which is incorporated wherein by reference in its entirety. See also, commonly assigned U.S. Pat. No. 5,625,800 entitled “A Sequencer Control Block Array External To A Host Adapter Integrated Circuit” of Michael D. Brayton et al. filed on Jun. 30, 1994; and also U.S. Pat. No. 5,564,023 entitled “Method for Accessing A Sequencer Control Block By A Host Adapter Integrated Circuit” of B. Arlen Young issued on Oct. 8, 1996, each of which is incorporated herein by reference in its entirety.
A prior art method for queuing SCBs for a system
100
, which included a processor
105
in a host system
106
and a host adapter device
120
with a sequencer
125
, used a one-dimensional linked list SCB queue
160
within a SCB array
155
in random access memory
150
. A device driver executing on microprocessor
105
managed host adapter
120
using SCBs, e.g., hardware control blocks, in SCB queue
160
. Each SCB in SCB queue
160
had a next queue site field Q_NEXT, sometimes referred to as field Q_NEXT, which was used to store a SCB site pointer that addressed the next SCB storage site in SCB queue
160
.
Queue
160
was delimited by head pointer
141
and tail pointer
142
. Head pointer
141
was the number of the site in SCB array
155
storing the SCB to be executed next, and tail pointer
142
was the number of the site in SCB array
155
containing the last SCB transferred from host system
106
. Next queue site field Q_NEXT in the site addressed by tail pointer
142
had an invalid value that was used to identify the SCB as the last in queue
160
in addition to tail pointer
142
.
When queue
160
was empty, head pointer
141
was an invalid value. When a new SCB was transferred from host system
106
to SCB array
155
, head pointer
141
and tail pointer
142
were changed to point to the storage site of the new SCB, i.e., were changed to valid values. Field Q_NEXT in the new SCB was set to an invalid value to indicate that the SCB was the last SCB in queue
160
.
As each new SCB was transferred from host system
106
to SCB array
155
, tail pointer
142
was used to identify the end of queue
160
. Field Q_NEXT in the SCB pointed to by tail pointer
142
was changed to point to the newly transferred SCB, and then tail pointer
142
was changed to point to the storage site of the newly transferred SCB.
A valid head pointer
141
indicated that one or more commands were available for transfer to one or more SCSI targets. The next target selected was specified by information within the SCB addressed by head pointer
141
. Host adapter
120
removed the SCB at the head of queue
160
for execution and selected the specified target. Head pointer
141
was changed to point to the next SCB in queue
160
, i.e., the value in field Q_NEXT of the SCB removed for execution was copied to head pointer
141
. When the selection process was complete, the command contained within the SCB was transferred to the target.
SCBs in queue
160
were executed and targets were selected in the order that the SCBs were received from host system
106
. This order is shown by the dashed line in FIG.
1
. SCBs were not inserted or removed from the middle of queue
160
.
Other methods are known for queuing SCSI command blocks for a SCSI target. See for example, U.S. Pat. Nos. 5,938,747 and 6,006,292, each of which is incorporated herein by reference. Independent of the method used to manage SCBs in a queue within the SCB array, SCBs are executed and targets are selected in the order that the SCBs were received from host system
106
. SCBs are not inserted into or removed from the middle of the queue within the SCB array.
SUMMARY OF THE INVENTION
According to an embodiment of this invention, a two-dimensional command block queue, stored in a memory of a host adapter, includes a plurality of command blocks in a first linked list, sometimes called a common queue of command blocks. In one embodiment, the first linked list is delimited by a stored head pointer and a stored tail pointer. In another embodiment, only the head pointer is stored.
The two-dimensional command block queue further includes another plurality of command blocks in a second linked list, sometimes called a string. There is a specific relationship between the first and second linked lists. Specifically, one and only one of the command blocks in the string is included in the plurality of command blocks in the first linked list. Only a tail pointer delimits the string.
A tail pointer list that is stored in a host adapter memory includes the tail pointer to a tail command block in the second linked list. The tail pointer is positioned in the tail pointer list so that the storage location is indexed using a device identifier associated with each of the command blocks in the string.
A string head pointer list is also stored in a host adapter memory, which, in one embodiment, is formed from a register in each of a plurality of memories. Following dequeuing the string from the two-dimensional command block queue, a pointer to the one and only one command block of the string that was in the common queue is included in the string head pointer list. The string is dequeued from the two-dimensional command block queue for processing of the string.
Following the dequeuing of the string from the two-dimensional command block queue for processing, the tail pointer to the string is not changed in the tail pointer list. This allows any new SCBs to be appended to the end of the string, while the string is being processed. This allows streaming of new SCBs to an I/O device that had previously been selected and is still connected to the host adapter.
This feature can provide a significant performance advantage, because even though the string is not included in the two-dimensional command block queue, the presence of the tail pointer in the tail pointer list makes it appear as though the string still was in the two-dimensional queue. Consequently, the same process is used to append new SCBs to a string independent of whether the string is included in the two-dimensional command block queue.
In one embodiment, memory in which the two-dimensional command block queue is stored is a first memory and the two-dimensional command block queue is stored in a command block array in the first memory. The first memory is internal to the host adapter in one embodiment, external to the host adapter in another embodiment, and includes both internal and external memory in still another embodiment. The various pointers and lists are stored in a second memory that is different from the first memory. The second memory can comprise multiple memory units.
The two-dimensional command block execution queue is a target command block execution queue if a host adapter is functioning in an initiator mode. Conversely, the two-dimensional command block execution queue is an initiator command block execution queue if the host adapter is functioning in a target mode. The host adapter can have both a target command block execution queue and an initiator command block execution queue if the host adapter functions in both initiator and target modes. In addition, this two-dimensional queue with the dequeuing is used to manage other functions of the host adapter associated

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