Granted Patent B2

US 8,554,976 · App. 13/179,074 · Granted Oct 8, 2013

Abstract

Claims (67)

1. A method for processing an incoming command from a host at a bridge, the incoming command destined for a target, the target having a storage management component and a separately accessible disk command queue, the method comprising:

determining, at the bridge, if the incoming command is a data command or a management command;

processing management commands separately from data commands, including:

forwarding, by the bridge, the incoming command to the storage management component of the target when the incoming command is a management command; and

when the incoming command is a data command, the bridge:

determining if the disk command queue on the target is full;

sending the incoming command to the disk command queue when the disk command queue is not full;

when the disk command queue is full, the bridge:

starting a timer, the timer having a predetermined length;

sending the incoming command to the disk command queue when the disk command queue becomes not full prior to the expiration of the timer; and

sending a rejection of the incoming command to the host only if, upon expiration of the timer, if the disk command queue is still full;

wherein the predetermined length of the time is selected to reduce a performance penalty for the host to process rejections of incoming data commands when there is a temporary disk command queue full state.

2. The method of claim 1 , wherein the predetermined length is less than it would take the host to reset itself and send a new data command upon receiving a rejection of a data command.

3. The method of claim 1 , wherein the predetermined length is longer than a worst-case target delay for processing a single data command.

4. The method of claim 1 , wherein the predetermined length is less than it would take the host to reset itself and send a new data command upon receiving a rejection of a data command and longer than a worst-case target delay for processing a single data command.

5. The method of claim 1 , wherein the predetermined length is dynamically determined by measuring performance of the host and basing the predetermined length at least partially upon the measured performance.

6. The method of claim 1 , wherein the predetermined length is dynamically determined by measuring performance of the target and basing the predetermined length at least partially upon the measured performance.

7. The method of claim 1 , wherein the predetermined length is selected to provide a guaranteed number of data or management commands processed per second.

8. The method of claim 1 , wherein the predetermined length is selected to prevent overloading the bridge command processing function with command rejections.

9. The method of claim 1 , wherein the incoming command is stored temporarily in a command FIFO on the bridge.

10. The method of claim 1 , wherein the host implements a USB Attached SCSI (UAS) protocol in which a target device cannot stall commands.

11. A bridge coupled between a host and a target, the target having a storage management component and a separately accessible disk command queue, the bridge comprising:

a command FIFO used to temporarily store incoming commands from the host;

a timer; and

a processor configured to:

determine if the incoming command is a data command or a management command;

processing management commands separately from data commands, including:

forward the incoming command to the storage management component of the target when the incoming command is a management command;

when the incoming command is a data:

determine if a disk command queue on the target is full;

send the incoming command to the disk command queue when the disk command queue is not full;

when the disk command queue is full:

start a timer, the timer having a predetermined length;

send the incoming command to the disk command queue when the disk command queue becomes not full prior to the expiration of the timer; and

send a rejection of the incoming command to the host only if, upon expiration of the timer, if the disk command queue is still full;

wherein the predetermined length of the time is selected to reduce a performance penalty for the host to process rejections of incoming data commands when there is a temporary disk command queue full state.

12. The bridge of claim 11 , wherein the bridge is a USB to SATA bridge.

13. The bridge of claim 11 , wherein the rejection indicates that the disk command queue on the target is full.

14. The bridge of claim 11 , wherein the management command is a command that cannot be head of line blocked by a data command.

15. The bridge of claim 11 , wherein the disk command queue has a limit of 32 commands.

16. The bridge of claim 11 , wherein the host implements a USB Attached SCSI (UAS) protocol in which a target device cannot stall commands.

17. An apparatus for processing an incoming command from a host at a bridge, the incoming command destined for a target, the target having a storage management component and a separately accessible disk command queue, the apparatus comprising:

means for determining if the incoming command is a data command or a management command;

means for processing management commands separately than data commands, including:

means for forwarding the incoming command to the storage management component of the target when the incoming command is a management command;

means for, when the incoming command is a data command:

determining if a disk command queue on the target is full;

sending the incoming command to the disk command queue when the disk command queue is not full;

when the disk command queue is full:

starting a timer, the timer having a predetermined length;

sending the incoming command to the disk command queue when the disk command queue becomes not full prior to the expiration of the timer; and

sending a rejection of the incoming command to the host only if, upon expiration of the timer, if the disk command queue is still full;

wherein the predetermined length of the time is selected to reduce a performance penalty for the host to process rejections of incoming data commands when there is a temporary disk command queue full state.

18. The apparatus of claim 17 , wherein the host implements a USB Attached SCSI (UAS) protocol in which a target device cannot stall commands.

19. A non-transitory program storage device readable by a machine tangibly embodying a program of instructions executable by the machine to perform a method for processing an incoming command from a host at a bridge, the incoming command destined for a target, the method comprising:

determining if the incoming command is a data command or a management command;

processing management commands separately than data commands, including:

forwarding the incoming command to a storage management component of the target when the incoming command is a management command;

when the incoming command is a data command:

determining if a disk command queue on the target is full;

sending the incoming command to the disk command queue when the disk command queue is not full;

when the disk command queue is full:

starting a timer, the timer having a predetermined length;

sending the incoming command to the disk command queue when the disk command queue becomes not full prior to the expiration of the timer; and

sending a rejection of the incoming command to the host only if, upon expiration of the timer, if the disk command queue is still full;

wherein the predetermined length of the time is selected to reduce a performance penalty for the host to process rejections of incoming data commands when there is a temporary disk command queue full state.

20. The non-transitory program storage device of claim 19 , wherein the host implements a USB Attached SCSI (UAS) protocol in which a target device cannot stall commands.

Assignments (8)