Abstract:
The present invention relates to a processor and a method for processing a data packet, the method including steps of decreasing a value of a first credit parameter when the data packet is admitted to a processor at least partly based on the value of the first credit parameter and a first limit of the first credit parameter, and increasing the value of the first credit parameter, in dependence on a data storage level in a buffer in which the data packet is stored before being admitted to the processor, the value of the first credit parameter not being increased, so as to become larger than a second limit of the first credit parameter, when the buffer is empty.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation of U.S. patent application Ser. No. 12/306,029, filed on Dec. 22, 2008, which claims priority under 35 U.S.C. §371 to International Application No. PCT/EP2007/055777, which claims priority to Swedish Patent Application No. 0601389-0, filed on Jun. 22, 2006, and U.S. Provisional Patent Application No. 60/817,095, filed on Jun. 29, 2006, the disclosures of each of which are hereby incorporated by reference as if fully stated herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a processor and a method for a processor comprising processing means, the method comprising the steps of admitting a data packet to the processing means based at least partly on a value of a first credit parameter and a first limit of the first credit parameter, and decreasing the value of the first credit parameter if the data packet is admitted to the processing means. 
       BACKGROUND 
       [0003]    In data processing, it is desired to reduce buffer capacity, i.e. storage capacity provided for storing data during queuing. 
         [0004]    In some known processors, incoming data traffic is admitted as quickly as possible without controlled admittance limitation, whereby limitations are given by processing capabilities. This will result in large requirements on buffer capacities in the processor. Also, data shaping can be used so that incoming data traffic is admitted to the processing element(s) of the processor so as to accomplish a constant bit rate, and/or a constant packet rate. 
         [0005]    In a processor, a shaper might be used for controlling incoming traffic based on a first resource of the processor, for example the bit rate capacity, and another shaper might be used to control incoming traffic based on a second resource of the processor, for example the data packet rate capacity. Such shapers usually have some credit parameter, for example in the form of a token bucket, based on which packets are admitted to the processing element(s) of the processor. The credit values are increased periodically with predetermined amounts, data packets are not admitted unless credit values of the shapers have reached a limit value, and the credit values are decreased when data packets are admitted. In such a processor, bursts might occur in the processor reasons illustrated by the following example: After a sequence of packets consuming a relatively large amount of the first resource and a relatively small amount of the second resource, e.g. relatively long data packets, the credit value of one of the shapers will reach a relatively high level. If such a packet sequence consuming a lot of the first resource and little of the second resource is followed by a sequence of packets consuming a relatively small amount of the first resource, e.g. relatively short data packets, a burst of packets will be permitted until the credit value having reached a relatively high level falls below the limit for admittance of packets. The risk of such data bursts will require a large buffer capacity downstream of the shapers. 
       SUMMARY 
       [0006]    It is an object of the invention to reduce buffer capacity in a processor. 
         [0007]    This object is reached with a method of the type mentioned initially, comprising the step of increasing the value of the first credit parameter, in dependence on a value of a second credit parameter, based on which a data packet is admitted to the processing means. 
         [0008]    As described closer below, the data packet, the admission of which is based on the value of the second credit parameter, can be identical or not identical with the data packet, the admission of which is based on the value of the first credit parameter. 
         [0009]    The invention is especially advantageous where the value of the first credit parameter is compared to a first limit of the first credit parameter, the data packet not being admitted to the processing means if the value of the first credit parameter is lower than the first limit. The invention will make it possible to compare the value of the first credit parameter to a second limit of the first credit parameter, the value of the first credit parameter not being increased, so as to become larger that the second limit of the first credit parameter, if the value of the second credit parameter is below a first limit of the second credit parameter. 
         [0010]    In particular, none of the credit values are allowed to increase while any of the other credit values are below a predetermined limit. This will avoid a build-up of large credit values, and will significantly reduce burst sizes, which in turn will allow lower downstream buffer capacity requirements. 
         [0011]    The first limit and the second limit of the first credit parameter can be different or equal. 
         [0012]    Preferably, the step of increasing the value of the first credit parameter is based at least partly on a first resource or a second resource of the processing means. Thereby, the credit levels, and therefore data admittance is adapted to chosen resources of the processing means, which will reduce buffer capacity requirements of the latter. As explained further below, the processing means resources can be any of a large amount of different types of features of the processing means. For example, one or more of the resources can be performance parameters relating to the processing means, e.g. the first resource can be a bit rate capacity of the processing means, and the second resource can be a data packet rate capacity of the processing means. Alternatively, one or more of the resources can be processing elements, adapted to process data. Alternatively or in addition, the step of increasing the value of the first credit parameter and/or the value of the second credit parameter, and/or decreasing the values of the first and the second credit parameter if the data packet is admitted to the processing means, can be based at least partly on an expected time period of residence in the processing means in the form of a processing pipeline, as described in the International patent application No. PCT/SE2005/001969, filed by the applicant, and incorporated herein by reference. 
         [0013]    Herein, the term “credit parameter” implies a parameter, the value of which is adjusted based on the admission of data packets. Thus, also the value of the second credit parameter is decreased if the data packet is admitted to the processing means. 
         [0014]    The object of the invention is also reached with a method of the type mentioned initially, comprising the step of increasing the value of the first credit, parameter, in dependence on a data storage level in a buffer in which the data packet is stored before admitted to the processing means. This prevent a build-up of a large credit at a processor data input interface not receiving traffic, or receiving a relatively small flow of traffic, for a period time, so that data burst from such an interface can be avoided when such a time period has passed. Preferably, the value of the first credit parameter is not increased, so as to become larger that a second limit of the first credit parameter, if the buffer is empty. 
         [0015]    The object of the invention is also reached with a processor according to any of the claims. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0016]    Below, the invention will be described in the detailed description with reference to the drawings, in which: 
           [0017]      FIG. 1  is a block diagram corresponding to a processor according to one embodiment of the present invention, 
           [0018]      FIG. 2  is a block diagram corresponding to a part of the processor to which the diagram in  FIG. 1  corresponds, 
           [0019]      FIG. 3  is a block diagram corresponding to a processor according to another embodiment of the present invention, and 
           [0020]      FIG. 4  is a block diagram corresponding to a processor according to a further embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  illustrates one embodiment of the present invention. A network processor  1  comprises processing means  2 . Two features of the processing means  2  are in this presentation referred to as a first and a second resource R 1 , R 2 . A resource as understood in this presentation can be any of a large amount of different types of features, and a few examples are given herein. In addition, in general, the processing means can present more than two resources, see below with reference to  FIG. 3 . One or more of the resources R 1 , R 2  can be processing elements, adapted to process data. Alternatively, one or more of the resources R 1 , R 2  can be performance parameters related to the processing means  2 . In this embodiment of the invention, both performance parameters are performance parameters. More specifically, the first resource R 1  is the bit rate capacity of the processing means  2 , and the second resource R 2  is the packet rate capacity of the processing means  2 . 
         [0022]    The processing means  2  can be any of a variety of known types, including an asynchronous processing pipeline, as described in said International patent application No. PCT/SE2005/001969, incorporated herein by reference. Thereby, any or all of the resources R 1 , R 2  can be performance parameters related to the processing means  2 , or processing elements of the processing pipeline, the amount of which can be considerably larger than two. Any of such processing elements can be an access point for access to a processing device, or engine, as describes in WO2004/010288, included herein by reference. 
         [0023]    Alternatively, the processing means  2  can be a RISC (Reduced Instruction Set Computer) processor, microcoded engine, hardcoded engine, or a combination of multiple processing means of one type or many types. 
         [0024]    Data traffic is forwarded from left to right in  FIG. 1 . Data packets D 1 , D 2 , D 3  enter the processor through a data input interface comprising an input port  3 , and are stored in an input buffer  4  before admitted to the processing means  2  in a manner described below. After exiting the processing means  2 , the packets are stored in an output buffer  6  before being transmitted through an output port  7 . 
         [0025]    Admission to the processing means  2  is determined by a first and a second shaper S 1 , S 2 , in the form of a bit rate shaper S 1  and a packet rate shaper S 2 , respectively. The bit rate shaper S 1  limits the bit rate to the processing means  2 . The limitation property of the bit rate shaper S 1  is chosen based on the first resource R 1 , i.e. the bit rate capacity of the processing means  2 . The packet rate shaper S 2  limits the flow of data packets to the processing means  2 . The limitation property of the packet rate shaper S 2  is chosen based on the second resource R 2 , i.e. the packet rate capacity of the processing means  2 . 
         [0026]    The shapers S 1 , S 2  can be provided in any suitable form, for example as a software program, or part thereof, or as digital or analogue circuits of electrical, optical or mechanical components. 
         [0027]    Reference is made to  FIG. 2 . Both shapers S 1 , S 2  use token bucket algorithms, so that admittance of data is based on a respective value CS 1 , CS 2  of a credit parameter. Each of these values CS 1 , CS 2 , herein also referred to as credit values CS 1 , CS 2 , are compared to a respective first limit L 1 S 2 , L 1 S 2 . If any of the credit values CS 1 , CS 2  is below the respective first limit L 1 S 2 , L 1 S 2 , no data traffic is allowed to pass the respective shaper. 
         [0028]    If neither of the credit values CS 1 , CS 2  is below the respective first limits L 1 S 2 , L 1 S 2  in the token buckets of the shapers S 1 , S 2 , the next packet D 1  in turn in the input buffer  4  is admitted to the processing means  2 . When the packet D 1  is admitted to the processing means, the credit value CS 1  of the bit rate shaper S 1  is reduced by an amount corresponding amount of bits of the packet D 1 , and the credit value CS 2  of the packet rate shaper S 2  is reduced by an amount corresponding to the number of packets admitted, i.e. one packet. 
         [0029]    As an alternative, the credit value CS 2  of the packet rate shaper S 2  can be adjusted as described in said International patent application No. PCT/SE2005/001969, incorporated herein by reference. Accordingly, each data packet D 1 , D 2 , D 3  can comprise a header with information, and the packet rate shaper S 2  can be adapted to read the information, which can be related to the cost of the data packet, i.e. to the longest time that the respective data packet D 1 , D 2 , D 3  keeps any processing element of the processing means  2  busy from accepting new data packets. Alternatively or in addition, such header information can be used to establish the identity of the resource, i.e. the processing element, to be engaged in processing of the respective packet D 1 , D 2 , D 3 . Further, the header can also include information about the size of the respective data packet. When the packet is admitted to the processing means, the credit value CS 2  of the packet rate shaper S 2  is reduced by an amount corresponding to the header information, e.g. cost information. 
         [0030]    A second limit L 2 S 1 , L 2 S 2  of the respective shaper S 1 , S 2  is higher than the respective first limit L 1 S 2 , L 1 S 2 , as indicated in  FIG. 2 . Alternatively the second limit L 2 S 1 , L 2 S 2  of the respective shaper S 1 , S 2  can be identical with the respective first limit L 1 S 2 , L 1 S 2 . If the credit value CS 1  of the bit rate shaper S 1  is below the second limit L 2 S 1 , the credit value CS 1  is periodically, e.g. every clock cycle of the processor  1 , incremented by a fixed credit amount. The value of the fixed credit amount is based on the frequency of the periodic increments (e.g. every clock cycle) and the first resource R 1 , i.e. the bit rate capacity of the processing means  2 . Similarly, if the credit value of the packet rate shaper S 2  is below the second limit L 2 S 2 , the credit value CS 2  is periodically incremented by a fixed credit amount, which is based on the frequency of the periodic increments and the second resource R 2 , i.e. the packet rate capacity of the processing means  2 . 
         [0031]    Preferably, the shapers S 1 , S 2  use a so called loose token bucket algorithm, i.e. the first limits L 1 S 1 , L 1 S 2  are zero, and when the both credit values CS 1 , CS 2  are non-negative, the next packet D 1  in turn in the input buffer  4  is admitted to the processing means  2 . 
         [0032]    If the credit value of any of the shapers S 1 , S 2  is below the first limit L 1 S 2 , L 1 S 2 , the credit value of the other shaper S 1 , S 2  is not incremented above a respective second limit L 2 S 1 , L 2 S 2 . Limiting the credit value of any of the shapers S 1 , S 2  to the respective second limit L 2 S 1 , L 2 S 2 , if the credit value of any other of the shapers S 1 , S 2  is below the first limit L 1 S 2 , L 1 S 2 , will reduce buffer capacity requirements of the processing means  2 . This is explained by the following example: 
         [0033]    Independent shapers, allowing unlimited increase of credit levels regardless of credit levels in other shapers, can not prevent the situations described as follows: After a sequence of packets consuming a relatively large amount of the first resource R 1  and a relatively small amount of the second resource R 2 , i.e. in this example relatively long data packets, the credit value of the second shaper S 2  will reach a relatively high level. If such a packet sequence consuming a lot of the first resource R 1  and little of the second resource R 2  is followed by a sequence of packets consuming a relatively small amount of the first resource R 1 , i.e. in this example relatively short data packets, a burst of packets will be permitted until credit value CS 2  of the second shaper S 2  falls below the first limit L 1 S 2 . Correspondingly, after a sequence of packets consuming a lot of the second resource R 2  and a only a little of the first resource R 1 , i.e. in this example relatively short data packets, the credit, value of the first shaper S 1  will reach a high level, allowing a burst of a following sequence of packets consuming a relatively small amount of the second resource R 2 , i.e. in this example relatively short data packets, until credit value CS 1  of the first shaper S 1  fails below the first limit L 1 S 1 . 
         [0034]    The invention will prevent a build-up of large credit values during data sequences consuming a large amount of one resource in relation to another resource of the processor. This will significantly reduce burst sizes, which in turn will allow lower downstream buffer capacity requirements. In the case of the processing means  2  being an asynchronous processing pipeline, as described in said International patent application No. PCT/SE2005/001969, the invention will reduce requirements on processing element buffers, in the form of a FIFO buffers, provided before the processing elements. 
         [0035]    As mentioned, the shapers S 1 , S 2  preferably use a loose token bucket algorithm, but alternatively, any other suitable admittance algorithm can be used. In case a so called strict token bucket algorithm is used, the first limits L 1 S 1 , L 1 S 2  can be positive, and the packet D 1  is admitted to the processing means  2  when the credit values CS 1 , CS 2  are at least as large so as to correspond to the respective first limits L 1 S 1 , L 1 S 2 . 
         [0036]    Where a strict token bucket algorithm is used, the first limit L 1 S 1 , L 1 S 2  of any or all of the shapers can be predetermined and identical for all data packets passing the respective shaper S 1 , S 2 . Alternatively, the first limit L 1 S 1 , L 1 S 2  can be individual for each packet, in which case the respective shaper S 1 , S 2  is adapted to read, before admittance, header information (e.g. of the type described above) of each data packet D 1 , D 2 , D 3 , and set the first limit L 1 S 1 , L 1 S 2  based on the header information. For example, the header information of the respective data packet D 1 , D 2 , D 3  could include a cost C 1 , C 2 , C 3 , corresponding to a first limit value L 1 S 1 , L 1 S 2  of one of the shapers, S 1 , S 2 . Thus, from the header information of the first packet D 1  in the input buffer  4 , the cost C 1  is read, and the first limit value L 1 S 1 , L 1 S 2  is determined as L 1 S 1  (or L 1 S 2 )=C 1 . 
         [0037]    Further, where a strict token bucket algorithm is used, the second limit L 2 S 1 , L 2 S 2 , (above which the credit value of the respective shaper S 1 , S 2  is not incremented if the credit value of the other shaper S 1 , S 2  is below its first limit L 1 S 2 , L 1 S 2 ), can either be identical with or higher than the first limit. L 1 S 2 , L 1 S 2 . In the latter case, the second limit L 2 S 1 , L 2 S 2  can be set individually for each packet to a value exceeding the first limit L 1 S 1 , L 1 S 2  by a predetermined amount. 
         [0038]      FIG. 3  illustrates a further embodiment of the present invention. The processing means  2  presents more than two features in the form of resources R 1 , R 2  . . . RN, which each can be any of a large amount of different types of features. For example, a first and a second resource R 1 , R 2  can be the bit rate capacity and the packet rate capacity, respectively, of the processing means  2 , and further resources can be processing elements, adapted to process data. 
         [0039]    Admission to the processing means  2  is determined by shapers S 1 , S 2  . . . SN, the amount of which is the same as the amount of processor means resources R 1 , R 2  . . . RN. The limitation property of the first shaper S 1  is chosen based on the first resource R 1 , and the limitation property of the second shaper S 2  is chosen based on the second resource R 2 , etc. 
         [0040]    Preferably, each shaper S 1 , S 2  . . . SN uses a token bucket algorithm, so that admittance of data is based on a respective value CS 1 , CS 2  . . . CSN of a credit parameter. If a credit value CS 1 , CS 2  . . . CSN is below a first limit L 1 S 2 , L 1 S 2  . . . L 1 SN, no data traffic is allowed to pass the respective shaper. Admittance of data traffic is carried out in a manner corresponding to what has been described above with reference to  FIGS. 1 and 2 . Thus, if the credit value CS 1 , CS 2  . . . CSN of any of the shapers S 1 , S 2  . . . SN is below the respective first limit L 1 S 2 , L 1 S 2  . . . L 1 SN, the respective credit value CS 1 , CS 2  . . . CSN is periodically, e.g. every clock cycle of the processor  1 , incremented by a respective fixed credit amount. The value of the respective fixed credit amount is based on the frequency of the periodic increments (e.g. every clock cycle) and the respective resource R 1 , R 2  . . . RN. 
         [0041]    If the credit value of any of the shapers S 1 , S 2  . . . SN is below the respective first limit L 1 S 2 , L 1 S 2  . . . L 1 SN, the credit value of the other shapers S 1 , S 2  . . . SN is not incremented above a respective second limit L 2 S 1 , L 2 S 2  . . . L 2 SN. The second limit L 2 S 1 , L 2 S 2  . . . L 2 SN can be above or identical with the respective first limit L 1 S 2 , L 1 S 2  . . . L 1 SN. 
         [0042]    In the embodiments described with reference to  FIG. 1-3 , the data packet D 1 , D 2 , D 3 , the admission of which is based on the value CS 2  of the second credit parameter, is identical with the data packet, the admission of which is based on the value CS 1  of the first credit parameter. However, as exemplified below with reference to  FIG. 4 , the invention is also adaptable so that admittance of a first data packet to the processing means  2  is based on a value of a first credit parameter, the value of the first credit parameter being increased in dependence on a value of a second credit parameter, based on which a second data packet is admitted to the processing means, the second data packet not being identical with the first data packet. In the example in  FIG. 4 , the first and second data packets enter the processor through separate interfaces. 
         [0043]    Referring to  FIG. 4 , a further embodiment of the invention is illustrated. A network processor  1  comprises processing means  2  in the form of an asynchronous processing pipeline  2 , as described closer in said International patent application No. PCT/SE2005/001969, included herein by reference, including asynchronous processing elements P 1 , . . . PK and a synchronous element  8 , with elastic buffering  9 ,  10 . As in the case of the embodiment described with reference to  FIGS. 1 and 2 , the processing means  2  can alternatively be provided in another form, for example as provided in a RISC-processor. 
         [0044]    As described closer in said International patent application No. PCT/SE2005/001969, included herein by reference, data packets D 11 , . . . D 1 M enter the processor through interfaces each comprising an input port  31 ,  32 , . . .  3 M, and are stored in respective input buffers  41 ,  42 ,  4 M, in addition to which a pipeline arbiter  11 , S 1 , S 2 , . . . SM comprises a scheduler  11  and a plurality of shapers S 1 , S 2 , . . . SM. In particular, for each pair of input port  31 ,  32 , . . .  3 M and input buffer  41 ,  42 , . . .  4 M, a shaper S 1 , S 2 , . . . SM is provided. Admission to the pipeline  2  is determined by the shapers S 1 , S 2 , . . . SM and the scheduler  11 , which operates according to a Round Robin algorithm, access to the pipeline being given to the shapers S 1 , S 2 , . . . SM in a continuous sequence of pollings by the scheduler  11 . 
         [0045]    Besides the Round Robin algorithm, alternative scheduling disciplines could be used, for example weighted fair queuing, deficit round robin, deficit weighted round robin, strict priority queuing, earliest deadline first, and first-come first-serve, 
         [0046]    Preferably, each shaper S 1 , S 2  . . . SM uses a token bucket algorithm, so that admittance of data is based on a respective value CS 1 , CS 2  . . . CSM of a credit parameter. If a credit value CS 1 , CS 2  . . . CSM is below a first limit L 1 S 2 , L 1 S 2  . . . L 1 SM, no data traffic is allowed to pass the respective shaper. If the credit value CS 1 , CS 2  . . . CSM of any of the shapers S 1 , S 2  . . . SM is below the respective first limit L 1 S 2 , L 1 S 2  . . . L 1 SM, the respective credit value CS 1 , CS 2  . . . CSM is periodically, e.g. every clock cycle of the processor  1 , incremented by a respective fixed credit amount. The value of the respective fixed credit amount is based on a resource of the processing means  2 , for example the packet rate capacity thereof, the frequency of the periodic increments (e.g. every clock cycle) and the amount of input ports  31 ,  32 , . . .  3 M. The resource of the processing means  2 , on which the fixed credit amount increments of the shapers S 1 , S 2  . . . SM are based, can alternatively be the bit rate capacity of the processing means  2 , or any other performance parameter thereof As a further alternative, the fixed credit amount increments of different shapers S 1 , S 2  . . . SM can be based on different processing elements P 1 , . . . PK, 8 to which traffic from the respective shaper is addressed. 
         [0047]    If the credit value of any of the shapers S 1 , S 2  . . . SM is below the respective first limit L 1 S 2 , L 1 S 2  . . . L 1 SN, the credit value of the other shapers S 1 , S 2  . . . SM is not incremented above a respective second limit L 2 S 1 , L 2 S 2  . . . L 2 SM. The second limit L 2 S 1 , L 2 S 2  . . . L 2 SM can be above or identical with the respective first limit L 1 S 2 , L 1 S 2  . . . L 1 SM. This prevents a build-up of a large credit in a shaper at an interface not receiving traffic, or receiving a relatively small flow of traffic for a period time, so that data burst from such an interface can be avoided when such a time period has passed. (It should be noted that in this presentation, a shaper being provided at an interface or an input port, indicates that it is either physically provided by, or functionally connected to the interface or the input port.) 
         [0048]    Still referring to  FIG. 4 , it should be mentioned that at each of the interfaces or input ports  31 ,  32 , . . .  3 M a plurality of shapers can be provided as described above with reference to  FIG. 1-3 , the credit of the shapers at each interface being respectively adjusted based on respective resources of the processing means. Thus, if the credit value of any of the shapers is below the respective first limit, the credit value of the other shapers at the same interface is not incremented above a respective second limit. Alternatively, if the credit value of any of the shapers is below the respective first limit, the credit value of ail other shapers, including the ones at other interfaces, is not incremented above a respective second limit. 
         [0049]    Alternatively or in addition, any of the embodiments described above with reference to  FIG. 1-4  can be adjusted so that if any of the input buffers  4 ,  41 ,  42 , . . .  4 M is empty, the credit value of the shaper (or shapers), adapted to receive traffic from this input buffer  4 ,  41 ,  42 , . . .  4 M, is not incremented above the second limit L 2 S 1 , L 2 S 2  . . . L 2 SM. This prevent a build-up of a large credit in a shaper at an interface not receiving traffic, or receiving a relatively small flow of traffic for a period time, so that data burst, from such an interface can be avoided when such a time period has passed.