Infiniband Credit-Less Flow Control For Long Distance Links
AssigneeInternational Business Machines Corporation
InventorsThomas A. Gregg, David Craddock
Life of this patent
Estimating the term…
Abstract
An Infiniband flow control scheme disables credit based flow control so that transmission distances can be extended. An Infiniband credit based flow control suffers from round trip time lag that slows transmission rates. Disabling Infiniband credit based flow control enables back to back packet transmission because credit counts are ignored. Nonetheless, packets can be lost due to overruns in a receive buffer, therefore, packet drop detection mechanisms are employed so that the Infiniband receiver can send requests to the Infiniband transmitter to temporarily slow its Infiniband transmission rate.
Claims20
In an Infiniband communication link that couples a first node and a second node, wherein each of the nodes comprises a transmitting device and a receiving device, the nodes exchange credit information over the link to control the other node's rate of data transmission over the link, and wherein the receiving devices each comprise a data buffer for storing transmitted data from the other node, a method of managing the communication link comprising the steps of:
- disabling a transmitting device from honoring the credit information sent by the other node over the link;
- the receiving devices monitoring for dropped packets that were sent by the other node due to lack of buffer space;
- and
- in response to detecting a dropped packet due to the lack of buffer space, the receiving device sending a request to the other node for decreasing the rate of transmission.
A receiver comprising:
- an input coupled to an IB link for receiving incoming IB packets at a first transmission rate;
- a data buffer coupled to the input for storing the incoming IB packets;
- an output coupled to the IB link for sending credit data over the IB link for indicating an amount of space in the data buffer;
- a monitor circuit coupled to the data buffer for detecting dropped packets due to lack of buffer space;
- and
- an output circuit coupled to the output for transmitting over the IB link a request for decreasing the first transmission rate to a slower transmission rate.
A transmitter comprising:
- an output coupled to an IB link for transmitting IB packets over the link at a controlled transmission rate;
- an input coupled to the IB link for receiving credit data and a request to decrease a current transmission rate to a slower transmission rate;
- a first circuit coupled to the input for interpreting the credit data and for controlling the current transmission rate for IB packets to be transmitted over the link in response thereto;
- a second circuit for disabling the first circuit in order for the transmitter to operate at an unrestricted transmission rate;
- and
- a third circuit coupled to the input for decreasing the unrestricted transmission rate in response to receiving the request to decrease a current transmission rate.
A program storage device readable by machine, wherein the machine comprises a transmitting device and a receiving device for exchanging credit information over an IB link to control a rate of data transmission received over the IB link, and a data buffer for storing received data and credit logic for counting credit information received, the program storage device tangibly embodying a program of instructions executable by the machine to perform the method steps comprising:
- disabling the transmitting device from honoring the credit information received over the link;
- the receiving device monitoring for dropped data packets due to lack of buffer space;
- and
- in response to detecting a dropped packet due to the lack of buffer space, sending a request for decreasing the rate of data transmission.
Dependencies are inferred from the claim text.