Programmable pseudo virtual lanes for fibre channel systems

• US 7,406,092 B2
• Filed: 07/20/2004
• Issued: 07/29/2008
• 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., Ross, Edward C.
• Primary Examiner(s): Levitan; Dmitry
• Application Number:
  US10/894,597
• Publication Number:
  US 20050018676A1
• Time in Patent Office: 1,470 Days
• Field of Search: 370/241, 370/242, 370/252, 370/389, 370/400, 370/412, 370/429, 370/437, 370/465, 370/477, 370/503, 709/228, 709/237, 709/238
• US Class Current: 370/437
• CPC Class Codes: H04L 49/25 Routing or path finding in a switch fabric
• CPC Class Codes: H04L 49/357 Fibre channel switches
• CPC Class Codes: H04L 49/506 Backpressure

Abstract

A method and switch element for assigning priority to pseudo virtual lanes (“PVL”) using a fibre channel switch element is provided. The method includes, assigning received R_RDYs based on a PVL distribution scheme; and determining traffic congestion on a PVL if there is no credit available to transfer frames from the PVL. A minimum bandwidth feature is enabled to avoid lower priority PVLs from getting no credit for transmitting frames; and distributing credit and R_RDYs based on frame age bits, wherein a lower priority PVL gets credit if a frame is waiting in the PVL for a longer duration compared to a higher priority PVL. The switch element includes, a PVL module having credit counters for plural PVLs; and a timer that monitors frame traffic for each PVL lane. If a PVL gets congested, then a state machine adjusts priority of R_RDY distribution scheme of other PVLs to transmit frames.

Claims

1. A method for assigning credit to a plurality of pseudo virtual lanes (“

PVLs”

) for a fibre channel switch element, comprising;

assigning an initial priority for each of the plurality of PVLs used by the fibre channel switch element;

monitoring credit assigned to each of the plurality of PVLs to transmit frames;

monitoring a transmission wait count for each of the plurality of PVLs, the transmit wait count indicating a time when a PVL is not able to transmit frames;

adjusting the initial priority for the PVL if credit assigned to the PVL has reached a threshold value;

adjusting the initial priority based on whether the transmission wait count for each of the plurality of PVLs has exceeded a threshold value providing an indicia for lane congestion;

receiving a primitive (R RDY) from a receiving port indicating that the receiving port has space available to store a frame; and

assigning the received R_RDY to a PVL from among the plurality of PVLs based on a PVL distribution scheme such that each PVL, regardless of PVL priority has access to a minimum bandwidth for transmitting and receiving Fibre Channel frames.

2. The method of claim 1, wherein the step of monitoring credit assigned to each of the plurality of PVLs to transmit frames comprises:

maintaining a credit counter value for each PVL;

decreasing the credit counter value when a PVL is assigned credit based on a received

R RDY;

determining if a PVL credit counter value has reached a threshold value; and

assigning credit to a PVL with a priority lower than the priority of the PVL whose credit

counter value has reached the threshold value.

3. The method of claim 1, wherein credit is assigned to a second PVL when a wait count value for a first PVL exceeds a threshold wait count value and the first PVL is determined to be congested.

4. The method of claim 3, wherein the threshold wait count value is a programmed value that is programmed by the fibre channel switch element firmware.

5. The method of claim 3, wherein a state machine for the fibre channel switch element monitors the threshold wait count value to determine congestion.

6. The method of claim 3, wherein to provide the minimum bandwidth to each PVL, a minimum bandwidth logic is enabled to assign credit to a PVL that has been waiting the longest to get credit.

7. The method of claim 6, wherein by enabling the minimum bandwidth logic, credit assignment based on PVL priority and traffic congestion is by passed and instead credit is assigned based on an age bit for each PVL, where the age bit indicates a duration for which the PVL has been waiting to receive credit.

8. The method of claim 1, wherein a PVL is used to allocate receive buffer credits at a fibre channel port and uses a primitive, R_RDY, for virtual lane credit management.