Method and system for buffer-to-buffer credit recovery in fibre channel systems using virtual and/or pseudo virtual lanes

• US 8,072,988 B2
• Filed: 10/15/2009
• Issued: 12/06/2011
• Est. Priority Date: 07/21/2003
• Status: Expired due to Fees

• Current Assignee: Marvell Asia Pte Limited (Marvell Technology Group Limited)
• Original Assignee: QLogic Corporation (Marvell Technology Group Limited)
• Inventors: Dropps, Frank R, Kohlwey, Ernest G, Ross, Edward C., Owen, Mark A.
• Primary Examiner(s): Lai, Andrew
• Application Number:
  US12/580,169
• Publication Number:
  US 20100128607A1
• Time in Patent Office: 782 Days
• Field of Search: 370/216, 370/228, 370/230, 370/236, 370/241, 370/390, 370/389, 370/397, 370/400, 370/412, 709/212, 709/234, 709/241, 702/179
• US Class Current: 370/397
• CPC Class Codes: H04L 49/357 Fibre channel switches
• CPC Class Codes: H04L 49/506 Backpressure

Abstract

A method and system for distributing credit using a fiber channel switch element is provided. The switch element includes, a wait threshold counter that is used to set up a status for a port that has to wait for certain duration to send a frame due to lack of buffer to buffer credit; a credit module that controls buffer to buffer credit for a transmit segment of the fiber channel switch element; and a virtual lane credit module with a counter that is incremented every time a frame assigned to a virtual lane is sent and decreased every time a VC_RDY is received. The method includes, determining if a VC_RDY primitive is received; and allocating credit to a virtual lane that is not at its maximum credit, after the VC_RDY primitive is received.

Claims

1. A method for distributing credit in a switch element, comprising:

(a) determining if (i) a port for the switch element using a plurality of virtual lanes has received a first flow control indicator, instead of a second flow control indicator used for managing credit for virtual lanes, where each virtual lane is identified by an identification number; and

(ii) if the switch element has internally generated the first flow control indicator for recovering lost credit due to loss of a frame;

(b) determining if a first virtual lane from among the plurality of virtual lanes has reached a maximum credit value allocated for the first virtual lane;

(c) if the first virtual lane has reached the maximum credit value, iteratively determining if another virtual lane for the port has not reached a maximum allocated credit value; and

allocating the recovered lost credit to a virtual lane from among the plurality of virtual lanes that has not reached the maximum allocated credit value;

(d) if the first flow control indicator is not received or generated for credit recovery in step (a);

determining if the second flow control indicator indicating that credit is available at a virtual lane at a destination port has been received by the port;

(e) determining if the virtual lane identified by the second flow control indicator in step (d) has already reached its maximum allocated credit; and

(f) iteratively analyzing each of the remaining plurality of virtual lanes and applying the credit based on the received second flow control indicator in step (d) to a virtual lane that has not reached a maximum allocated credit even if a virtual lane identification number indicates that credit be allocated to a different virtual lane.

2. The method of claim 1, wherein a processor for the switch element resets a link if one or more of credit loss and frame loss exceeds a threshold value.

3. The method of claim 1, wherein the switch element generates statistical information for trend analysis on a link when a loss of more than a threshold number of frames is detected.

4. The method of claim 1, wherein the switch element generates statistical information for trend analysis on a link when a loss of more than a threshold number of credits is detected.

5. A method for distributing credit in a network system having a switch element, comprising:

(a) detecting lost credit at a port for the switch element if fewer than expected first indicators and second indicators are received between third indicators;

wherein the first indicators indicate credit for a virtual lane of a port supporting a plurality of virtual lanes and each virtual lane identified by an identification number and allocated a maximum credit value;

the second indicators indicate credit at a receive segment of a port; and

the third indicator is used for tracking lost credit in the network system;

(b) iteratively determining if a virtual lane from among the plurality of virtual lanes for the port has not reached its maximum allocated credit value; and

(c) allocating the recovered lost credit from step (a) to the virtual lane from among the plurality of virtual lanes, that has not reached the maximum allocated credit value;

wherein the recovered lost credit is allocated to a virtual lane that is different from the virtual lane identified by the first indicator, if the identified virtual lane has reached the maximum allocated credit value.

6. The method of claim 5, further comprising:

determining if a third indicator is lost or extra credit is received if a first indicator or a second indicator is received when a third indicator is expected; and

setting a status bit to indicate if a third indicator was lost or an extra first indicator or second indicator is received.

7. A switch element for routing frames, comprising:

a plurality of ports with each port including (i) a transmit segment for transmitting frames and a receive segment for receiving frames;

(ii) a wait threshold counter configured to monitor a duration that a transmit segment has to wait for sending a frame due to lack of credit and generating a status signal if the duration exceeds a programmable threshold value;

(iii) a credit module configured to control credit for a transmit segment of a port; and

(iv) a virtual lane credit module having a counter that is incremented every time a frame assigned to a virtual lane is sent and decreased every time a first indicator is received, the first indicator indicating that credit is available at a virtual lane at a destination port;

wherein for allocating recovered lost credit among a plurality of virtual lanes, based on a received second indicator and a received first indicator; and

a second indicator generated by the switch element for lost data frames, the switch element (a) determines if a first virtual lane from among the plurality of virtual lanes supported by a port has reached a maximum credit value allocated for the first virtual lane;

(b) iteratively determines if another virtual lane for the port has not reached a maximum allocated credit value; and

(c) allocates the recovered lost credit to a virtual lane from among the plurality of virtual lanes, that has not reached the maximum allocated credit value.

8. The switch element of claim 7, wherein the virtual lane to which credit is allocated is different from the virtual lane identified by the first indicator used for the lost credit, if the identified virtual lane has reached its maximum allocated value.

9. The switch element of claim of 8, wherein if lost frames are detected, then the logic module generates an equivalent number of the second indicators that should have been received and sends the generated second indicators to a device on another end of a link.

10. The switch element of claim 8, wherein the switch element resets a link if loss of more than a threshold number of frame credits is detected.

11. The switch element of claim 8, wherein the switch element resets a link if loss of more than a threshold number of the first indicators and the second indicators is detected.

12. The switch element of claim 8, wherein the switch element generates statistical information for trend analysis on a link when a loss of more than a threshold number of frames is detected.

13. The switch element of claim 8, wherein the switch element generates statistical information for trend analysis on a link when a loss of more than a threshold number of credits is detected.

14. The switch element of claim 8, wherein the switch element generates statistical information for trend analysis on a link, if loss of more than a threshold number of the first indicators is detected.

15. The switch element of claim 8, wherein the switch element generates statistical information for trend analysis on a link, if loss of more than a threshold number of the second indicators is detected.

16. The switch element of claim 7, further comprising:

a logic module that generates a status signal if loss of more than a threshold number of frame credits due to loss of the first indicator and the second indicator is detected, wherein the second indicator is a link primitive indicating available credit at a receive segment of a port.

17. The switch element of claim 16, wherein the threshold number is programmable.

18. The switch element of claim 16, wherein the threshold number is fixed.