Method and system for ordering priority commands on a commodity disk drive

• US 6,301,639 B1
• Filed: 07/26/1999
• Issued: 10/09/2001
• Est. Priority Date: 07/26/1999
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Cleavinger, Richard Curtis, Prosch, Kent D.
• Primary Examiner(s): Verbrugge, Kevin
• Application Number:
  US09/360,261
• Time in Patent Office: 806 Days
• Field of Search: 711/4, 711/111, 711/112, 711/154, 710/5, 710/6
• US Class Current: 711/112
• CPC Class Codes: G06F 3/0611 in relation to response time
• CPC Class Codes: G06F 3/0613 in relation to throughput
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/0674 Disk device

Abstract

In a computer system including a disk controller and a disk drive, the disk controller determines whether to issue a command to the disk drive by considering both a priority level associated with the command, and a pending workload of the disk drive.

Claims

1. A method for determining whether to issue a command from a disk controller to a disk drive, said disk controller maintaining a pending workload value that represents a pending workload of said disk drive, said command having an associated priority level, said disk controller performing the steps of:

(A) determining whether said priority level is greater than or equal to a threshold priority level;

(B) determining whether said pending workload value is less than a first threshold value, when step A determines said priority level is greater than or equal to said threshold priority level;

(C) determining whether said pending workload value is less than a second threshold value, when step A determines said priority level is not greater than or equal to said threshold priority level; and

(D) issuing said command to said disk drive when either step B determines said pending workload value is less than said first threshold value, or step C determines said pending workload value is less than said second threshold value,

 

wherein said second threshold value is not equal to said first threshold value, and said first threshold value and said second threshold value are selected to favor issuing said command when said priority level is greater than or equal to said threshold priority level.

2. The method recited in claim 1, wherein said disk drive includes a disk queue containing outstanding commands that have been issued to, but not yet executed by, said disk drive.

3. The method recited in claim 2, wherein said disk drive is capable of reordering said outstanding commands on said disk queue.

4. The method recited in claim 1, wherein said pending workload value is a count of outstanding commands, which have been issued to, but not yet executed by, said disk drive.

5. The method recited in claim 4, wherein said count of outstanding commands is incremented when said command is issued to said disk drive, and decremented when said command is executed by said disk drive.

6. The method recited in claim 1, wherein said priority level is one of a plurality of priority levels.

7. A disk controller that determines whether to issue a command to a disk drive, said command having an associated priority level, said disk controller comprising:

(A) a memory for storing a pending workload value that represents a pending workload of said disk drive;

(B) a processor for performing;

(1) a first comparison to determine whether said priority level is greater than or equal to a threshold priority level;

(2) a second comparison to determine whether said pending workload value is less than a first threshold value, when said first comparison determines that said priority level is greater than or equal to said threshold priority level;

(3) a third comparison to determine whether said pending workload value is less than a second threshold value, when said first comparison determines that said priority level is not greater than or equal to said threshold priority level; and

 

wherein said processor issues said command to said disk drive when either said second comparison determines said pending workload value is less than said first threshold value, or said third comparison determines said pending workload value is less than said second threshold value, and

 

wherein said second threshold value is not equal to said first threshold value, and said first threshold value and said second threshold value are selected to favor issuing said command when said priority level is greater than or equal to said threshold priority level.

8. The disk controller recited in claim 7, wherein said disk drive includes a disk queue containing outstanding commands that have been issued to, but not yet executed by, said disk drive.

9. The disk controller recited in claim 8, wherein said disk drive is capable of reordering said outstanding commands on said disk queue.

10. The disk controller recited in claim 7, wherein said pending workload value is a count of outstanding commands, which have been issued to, but not yet executed by, said disk drive.

11. The disk controller recited in claim 10, wherein said processor increments said count of outstanding commands when said command is issued to said disk drive, and decrements said count of outstanding commands when said command is executed by said disk drive.

12. The disk controller recited in claim 7, wherein said priority level is one of a plurality of priority levels.

13. A memory media that stores a program for a disk controller that determines whether to issue a command to a disk drive, said disk controller maintaining a pending workload value that represents a pending workload of said disk drive, said command having an associated priority level, said memory media comprising:

(A) means for controlling said disk controller to determine whether said priority level is greater than or equal to a threshold priority level;

(B) means for controlling said disk controller to determine whether said pending workload value is less than a first threshold value, when means A determines said priority level is greater than or equal to said threshold priority level;

(C) means for controlling said disk controller to determine whether said pending workload value is less than a second threshold value, when means A determines said priority level is not greater than or equal to said threshold priority level; and

(D) means for controlling said disk controller to issue said command to said disk drive when either means B determines said pending workload value is less than said first threshold value, or means C determines said pending workload value is less than said second threshold value,

 

wherein said second threshold value is not equal to said first threshold value, and said first threshold value and said second threshold value are selected to favor issuing said command when said priority level is greater than or equal to said threshold priority level.

14. The memory media recited in claim 13, wherein said disk drive includes a disk queue containing outstanding commands that have been issued to, but not yet executed by, said disk drive.

15. The memory media recited in claim 14, wherein said disk drive is capable of reordering said outstanding commands on said disk queue.

16. The memory media recited in claim 13, wherein said pending workload value is a count of outstanding commands, which have been issued to, but not yet executed by, said disk drive.

17. The memory media recited in claim 16, further comprising means for controlling said disk controller to increment said count of outstanding commands when said command is issued to said disk drive, and to decrement said count of outstanding commands when said command is executed by said disk drive.

18. The memory media recited in claim 13, wherein said priority level is one of a plurality of priority levels.