US 8,045,472 B2 · Credit management when resource granularity is larger than credit granularity

Abstract

In one embodiment, a receiver on a credit-based flow-controlled interface is configured to free one or more data credits early when a data payload is received that incurs fewer unused data credits within a buffer memory that is allocated at a coarser granularity than the data credits. In another embodiment, header credits and data credits are dynamically adjusted based on actual packet data payload sizes.

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Drawings

Claims18

Dependent claims

An apparatus comprising:

a receiver comprising a credit management unit configured to manage flow control credits for an interface to which the receiver is coupled during use, wherein each packet received on the interface comprises a packet header and optionally packet data, and wherein the packet data is measured in terms of data credits in the flow control credits dependent on a size of the packet data, wherein each data credit represents a fixed number of data bytes;
and
a buffer memory coupled to the receiver and configured to store packet headers and packet data corresponding to packets that are received on the interface by the receiver, wherein the buffer memory is allocable by the receiver in buffer units which are N times the size of the data credit, wherein N is an integer greater than one;
and
wherein a total number of data credits is equal to N times a number of buffer units in the buffer memory that are available to store packet data, and wherein the credit management unit is configured to reserve a plurality of the total data credits based on a maximum number of data credits that are unusable if packet data does not fill a buffer unit and further based on a number of packets that are permitted to be in flight concurrently, and wherein the credit management unit is configured to free one or more data credits in response to receiving packet data for a given packet that incurs fewer than the maximum number of unusable data credits, wherein the credit management unit is configured to free the one or more data credits prior to the given packet being consumed.

2 more elements

A method comprising:

receiving a packet from an interface, wherein the packet comprises packet data that consumes one or more data credits at a transmitter on the interface based on a size of the packet data, wherein each data credit represents a fixed number of data bytes;
storing the packet data in a buffer memory, wherein the buffer memory is allocable to store packet data in buffer units which are N times the size of the data credit, wherein N is an integer greater than one, and wherein up to N−1 data credits are unusable responsive to the packet data not filling a buffer unit allocated to store the packet data;
and
responsive to receiving the packet and prior to the packet being consumed, determining that the packet data incurs fewer than N−1 unusable data credits, and freeing one or more data credits that are useable responsive to the determining.

1 more element

An apparatus comprising:

a receiver comprising a credit management unit configured to manage flow control credits for an interface to which the receiver is coupled during use, wherein each packet received on the interface comprises a header and optionally data, and wherein the header is measured in terms of one or more header credits for flow control on the interface, and wherein data is measured in terms of one or more data credits for flow control on the interface, each data credit representing a fixed number of data bytes;
and
a buffer memory coupled to the receiver and configured to store packet headers and packet data corresponding to packets that are received on the interface by the receiver;
and
wherein the credit management unit is configured to dynamically adjust a first amount of the buffer memory allocated to store packet headers and a second amount of the buffer memory allocated to store the packet data responsive to a size of the packet data in one or more received packets, and wherein the credit management unit is configured to free credits to a transmitter on the interface responsive to the dynamic adjustments, and wherein the credit management unit is configured to increase the first amount and decrease the second amount, and wherein the credit management unit is configured to withhold one or more data credits corresponding to a consumed packet and to instead free one or more header credits to effect the modification, and wherein a header credit represents N−1 times the fixed number of data bytes that are represented by a data credit, and wherein the credit management unit is configured to withhold N−1 data credits to free one header credit.

2 more elements

Dependencies are inferred from the claim text.

Description6,581 words

Summary798 words

#1. Field of the Invention

#This invention is related to digital systems and, more particularly, to credit management for credit-based flow control mechanisms for interfaces in digital systems.

#2. Description of the Related Art

Brief description of the drawings10 figures

#The following detailed description makes reference to the accompanying drawings, which are now briefly described.

#FIG. 1 is a block diagram of one embodiment of a digital system.

#FIG. 2 is a block diagram of one embodiment of memory buffer allocation.

Detailed description5,543 words

#While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description. As used throughout this application, the word “may” is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words “include”, “including”, and “includes” mean including, but not limited to.

#Turning now to FIG. 1, a block diagram of one embodiment of a system 10 is shown. In the illustrated embodiment, the system 10 includes a transmitter 12, a receiver 14, a buffer memory 16, and optionally a packet target 18. The transmitter is coupled to an interface 20 to which the receiver 14 is also coupled. The buffer memory 16 is coupled to the receiver 14 and the target 18.

#The transmitter 12 is configured to maintain header credits and data credits, which indicate how much packet header and packet data traffic the receiver 14 is currently able to accept. For example, in FIG. 1, the transmitter 12 may include a header credit register 22 and a data credit register 24. During initialization of the system 10, and possibly at other points during operation at which the interface 20 is reset, the receiver 14 may determine the number of header credits and data credits to advertise to the transmitter 12. The transmitter 12 may initialize the registers 22 and 24 with the advertised credits. As the transmitter 12 transmits packet headers and packet data, the transmitter 12 may deduct the credits consumed by the transmitted headers and data. The receiver 14 may transmit freed credits back to the transmitter 12, which may add the freed credits to the registers 22 and 24. Thus, at any given point in time, the transmitter 12 may control how much information is transmitted over the interface 20 responsive to the credits in the registers 22 and 24. If not enough credits are available for a given transmission, for example, the transmitter 12 may delay transmission until the needed number of credits become available.

Facts

Application

12/344,949Filed 29 Dec 2008

Published

US 2010/0165842 A11 Jul 2010

Granted

25 Oct 2011

Term ends

20 May 2029

Estimated · how

20 years from earliest known nonprovisional domestic filing plus recorded patent term adjustment, including 142 days of adjustment. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification6 codes

G06F 13/385
Using universal interface adapter: for adaptation of a particular data processing system to different peripheral devices
H04L 47/10
Traffic control in data switching networks: flow control; Congestion control
H04L 47/39
Flow control; Congestion control: credit based
H04L 49/90
Packet switching elements: buffering arrangements

Credit management when resource granularity is larger than credit granularity

Life of this patent

Credit management when resource granularity is larger than credit granularity

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims18

Description6,581 words

Drawings

Classification6 codes

Life of this patent

Description6,581 words