Abstract:
In some embodiments, a low overhead mechanism for offloading copy operations is presented. In this regard, a copy agent is introduced to receive a copy request, to notify of copy completion before the copy has been performed, and to perform the copy. Other embodiments are also disclosed and claimed.

Description:
FIELD OF THE INVENTION  
       [0001]     Embodiments of the present invention generally relate to the field of data transfer, and, more particularly to a low overhead mechanism for offloading copy operations.  
       BACKGROUND OF THE INVENTION  
       [0002]     Applications move or copy data from one memory location (address) to another. Typically, the data movement or copy operations are performed by the CPU. However, since the CPU typically has to fetch the data from memory (which is much slower), the copy operation tends to be rather slow. To speed up the copy operation and avoid stalling the CPU, some systems employ copy engines. The main overhead in dealing with copy engines is the setup and notification overhead. The CPU typically initiates the operation of the DMA engine and continues performing other work. Completion notification is provided using traditional mechanisms such as polling or interrupts. Both polling and interrupts can be a source of inefficiency since the processor is occupied during the process. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]     The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements, and in which:  
         [0004]      FIG. 1  is a block diagram of an example electronic appliance suitable for implementing control and copy agents, in accordance with one example embodiment of the invention;  
         [0005]      FIG. 2  is a block diagram of an example copy agent architecture, in accordance with one example embodiment of the invention;  
         [0006]      FIG. 3  is a block diagram of an example control agent architecture, in accordance with one example embodiment of the invention; and  
         [0007]      FIG. 4  is a flow chart of an example method for early copy completion, in accordance with one example embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0008]     In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that embodiments of the invention can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form in order to avoid obscuring the invention.  
         [0009]     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.  
         [0010]      FIG. 1  is a block diagram of an example electronic appliance suitable for implementing control and copy agents, in accordance with one example embodiment of the invention. Electronic appliance  100  is intended to represent any of a wide variety of traditional and non-traditional electronic appliances, laptops, desktops, servers, cell phones, wireless communication subscriber units, wireless communication telephony infrastructure elements, personal digital assistants, set-top boxes, or any electric appliance that would benefit from the teachings of the present invention. In accordance with the illustrated example embodiment, electronic appliance  100  may include one or more of processor(s)  102 , control agent(s)  104 , memory controller  106 , copy agent  108 , system memory  110 , input/output controller  112 , and input/output device(s)  114  coupled as shown in  FIG. 1 .  
         [0011]     Processor(s)  102  may represent any of a wide variety of control logic including, but not limited to one or more of a microprocessor, a programmable logic device (PLD), programmable logic array (PLA), application specific integrated circuit (ASIC), a microcontroller, and the like, although the present invention is not limited in this respect.  
         [0012]     Control agent  104  may have an architecture as described in greater detail with reference to  FIG. 3 . Control agent  104  may also perform one or more methods for early copy completion, such as the method described in greater detail with reference to  FIG. 4 . While shown as being part of processor  102 , control agent  104  may well be part of another component, or may be implemented in software or a combination of hardware and software.  
         [0013]     Memory controller  106  may represent any type control logic that interfaces system memory  110  with the other components of electronic appliance  100 . In one embodiment, the connection between processor(s)  102  and memory controller  106  may be referred to as a front-side bus. In another embodiment, memory controller  106  may be referred to as a north bridge. Memory controllers can be integrated with the processor on the same die.  
         [0014]     Copy agent  108  may have an architecture as described in greater detail with reference to  FIG. 2 . Copy agent  108  may also perform one or more methods for early copy completion, such as the method described in greater detail with reference to  FIG. 4 . While shown as being part of memory controller  106 , copy agent  108  may well be part of another component, for example processor(s)  102  or input/output controller  112 , or may be implemented in software or a combination of hardware and software.  
         [0015]     System memory  110  may represent any type of memory device(s) used to store data and instructions that may have been or will be used by processor(s)  102 . Typically, though the invention is not limited in this respect, system memory  110  will consist of dynamic random access memory (DRAM). In one embodiment, system memory  110  may consist of Rambus DRAM (RDRAM). In another embodiment, system memory  110  may consist of double data rate synchronous DRAM (DDRSDRAM). The present invention, however, is not limited to the examples of memory mentioned here.  
         [0016]     Input/output (I/O) controller  112  may represent any type of chipset or control logic that interfaces I/O device(s)  114  with the other components of electronic appliance  100 . In one embodiment, I/O controller  112  may be referred to as a south bridge. In another embodiment, I/O controller  112  may comply with the Peripheral Component Interconnect (PCI) Express™ Base Specification, Revision 1.0a, PCI Special Interest Group, released Apr. 15, 2003. I/O controller  112  may have internal status registers relating to its operation and the operation of I/O device(s)  114 .  
         [0017]     Input/output (I/O) device(s)  114  may represent any type of device, peripheral or component that provides input to or processes output from electronic appliance  100 . In one embodiment, though the present invention is not so limited, I/O device(s)  114  may include a network interface controller with the capability to perform Direct Memory Access (DMA) operations to copy data into system memory  110 . In this respect, there may be a software Transmission Control Protocol/Internet Protocol (TCP/IP) stack being executed by processor(s)  102  that will process the contents in system memory  110  as a result of a DMA by I/O device  114  as TCP/IP packets are received. I/O device(s)  114  in particular, and the present invention in general, are not limited, however, to network interface controllers. In other embodiments, at least one I/O device  114  may be a graphics controller or disk controller, or another controller that may benefit from the teachings of the present invention.  
         [0018]      FIG. 2  is a block diagram of an example copy agent architecture, in accordance with one example embodiment of the invention. As shown, copy agent  108  may include one or more of control logic  202 , memory  204 , interface  206 , and copy engine  208  coupled as shown in  FIG. 2 . In accordance with one aspect of the present invention, to be developed more fully below, copy agent  108  may include a copy engine  208  comprising one or more of notify services  210 , copy services  212 , and/or complete services  214 . It is to be appreciated that, although depicted as a number of disparate functional blocks, one or more of elements  202 - 214  may well be combined into one or more multi-finctional blocks. Similarly, copy engine  208  may well be practiced with fewer finctional blocks, i.e., with only copy services  212 , without deviating from the spirit and scope of the present invention, and may well be implemented in hardware, software, firmware, or any combination thereof. In this regard, copy agent  108  in general, and copy engine  208  in particular, are merely illustrative of one example implementation of one aspect of the present invention. As used herein, copy agent  108  may well be embodied in hardware, software, firmware and/or any combination thereof.  
         [0019]     Copy agent  108  may have the ability to receive a copy request, to notify of copy completion before the copy has been performed, and to perform the copy. In one embodiment, copy agent  108  may indicate when the copy has actually been completed. In another embodiment, copy agent  108  may perform copies and notifications without interrupting processor(s)  102 , thereby improving performance.  
         [0020]     As used herein control logic  202  provides the logical interface between copy agent  108  and its host electronic appliance  100 . In this regard, control logic  202  may manage one or more aspects of copy agent  108  to provide a communication interface to electronic appliance  100 , e.g., through memory controller  106 .  
         [0021]     According to one aspect of the present invention, though the claims are not so limited, control logic  202  may selectively invoke the resource(s) of copy engine  208  in response to receiving a command such as, e.g. data copy from processor(s)  102 . As part of an example method for early copy completion, as explained in greater detail with reference to  FIG. 4 , control logic  202  may selectively invoke notify services  210  that may make the details of a copy globally available and notify of completion of the copy before the copy has been performed. Control logic  202  also may selectively invoke copy services  212  or complete services  214 , as explained in greater detail with reference to  FIG. 4 , to perform memory copies or to signal the actual completion of copies, respectively. As used herein, control logic  202  is intended to represent any of a wide variety of control logic known in the art and, as such, may well be implemented as a microprocessor, a micro-controller, a field-programmable gate array (FPGA), application specific integrated circuit (ASIC), programmable logic device (PLD) and the like. In some implementations, control logic  202  is intended to represent content (e.g., software instructions, etc.), which when executed implements the features of control logic  202  described herein.  
         [0022]     Memory  204  is intended to represent any of a wide variety of memory devices and/or systems known in the art. According to one example implementation, though the claims are not so limited, memory  204  may well include volatile and non-volatile memory elements, possibly random access memory (RAM) and/or read only memory (ROM). Memory  204  may be used to store the buffer addresses and lengths of copies that are to be completed, for example.  
         [0023]     Interface  206  provides a path through which copy agent  108  can communicate with memory controller  106 . In one embodiment, interface  206  may represent any of a wide variety of interfaces or controllers known in the art. In another embodiment, interface  206  may comply with the System Management Bus (SMBus) Specification, Version  2 . 0 , SBS Implementers Forum, released Aug. 3, 2000.  
         [0024]     Notify services  210 , as introduced above, may provide copy agent  108  with the ability to make the details of a copy globally available and notify of completion of the copy before the copy has been performed. In one example embodiment, notify services  210  may send source and destination buffer addresses, along with their lengths, to processor(s)  102 . Control agent  104  may store the address and length in a table as described with reference to  FIG. 3 . Notify services  210  may then receive an acknowledgement from each control agent  104  that the addresses and lengths have been stored. Notify services  210  may then send a notification of copy completion to the requesting processor  102 , even though the copy has not yet been performed.  
         [0025]     As introduced above, copy services  212  may provide copy agent  108  with the ability to perform memory copies. In one example embodiment, copy services  212  may copy data from a network controller to system memory  110 . In another embodiment, copy services  212  may copy data from system memory  110  to an internal cache of processor(s)  102 . The copies may have sources and destinations of other local or remote devices as well.  
         [0026]     Complete services  214 , as introduced above, may provide copy agent  108  with the ability to signal the actual completion of copies. In one embodiment, complete services  214  may send an indication to processor(s)  102  indicating a buffer address of copies that have completed. Control agent  104  may remove the address from a table of pending copies as described with reference to  FIG. 3 .  
         [0027]      FIG. 3  is a block diagram of an example control agent architecture, in accordance with one example embodiment of the invention. As shown, control agent  104  may include one or more of control logic  302 , memory  304 , interface  306 , and control engine  308  coupled as shown in  FIG. 3 . In accordance with one aspect of the present invention, to be developed more fully below, control agent  104  may include a control engine  308  comprising one or more of table services  310 , compare services  312 , and/or stall services  314 . It is to be appreciated that, although depicted as a number of disparate functional blocks, one or more of elements  302 - 314  may well be combined into one or more multi-functional blocks. Similarly, control engine  308  may well be practiced with fewer functional blocks, i.e., with only stall services  314 , without deviating from the spirit and scope of the present invention, and may well be implemented in hardware, software, firmware, or any combination thereof. In this regard, control agent  104  in general, and control engine  308  in particular, are merely illustrative of one example implementation of one aspect of the present invention. As used herein, control agent  104  may well be embodied in hardware, software, firmware and/or any combination thereof.  
         [0028]     Control agent  104  may have the ability to store a buffer address and length associated with a copy to be completed, to compare an address and length within an instruction to the stored address and length, and to stall the instruction if the addresses overlap. In one embodiment, control agent  104  may maintain a table of pending copies that have not yet completed to determine which instructions should not be allowed to execute. In another embodiment, control agent  104  may clear entries in the table when a notification has been received that the copies have been completed.  
         [0029]     As used herein control logic  302  provides the logical interface between copy agent  108  and its host electronic appliance  100 . In this regard, control logic  302  may manage one or more aspects of copy agent  108  to provide a communication interface to electronic appliance  100 , e.g., through processor(s)  102 .  
         [0030]     According to one aspect of the present invention, though the claims are not so limited, control logic  302  may selectively invoke the resource(s) of control engine  308 . As part of an example method for early copy completion, as explained in greater detail with reference to  FIG. 4 , control logic  302  may selectively invoke table services  310  that may maintain a table of pending copies. Control logic  302  also may selectively invoke compare services  312  or stall services  314 , as explained in greater detail with reference to  FIG. 4 , to compare addresses within instructions to be executed with addresses stored in the pending copy table or to block the execution of loads and store operations if the address within an instruction matches an address in the pending copy table, respectively. As used herein, control logic  302  is intended to represent any of a wide variety of control logic known in the art and, as such, may well be implemented as a microprocessor, a micro-controller, a field-programmable gate array (FPGA), application specific integrated circuit (ASIC), programmable logic device (PLD) and the like. In some implementations, control logic  302  is intended to represent content (e.g., software instructions, etc.), which when executed implements the features of control logic  302  described herein.  
         [0031]     Memory  304  is intended to represent any of a wide variety of memory devices and/or systems known in the art. According to one example implementation, though the claims are not so limited, memory  304  may well include volatile and non-volatile memory elements, possibly random access memory (RAM) and/or read only memory (ROM). Memory  304  may be used to store a table of buffer addresses and lengths of pending copies, for example. Memory  304  may also store instructions that are being blocked from executing due to stall services  314 .  
         [0032]     Interface  306  provides a path through which control agent  104  can communicate with processor  102 . In one embodiment, interface  306  may represent any of a wide variety of interfaces or controllers known in the art. In another embodiment, interface  206  may comply with the System Management Bus (SMBus) Specification, Version 2.0, SBS Implementers Forum, released Aug. 3, 2000.  
         [0033]     Table services  310 , as introduced above, may provide control agent  104  with the ability to maintain a table of pending copies. In one example embodiment, table services  310  receives buffer addresses and lengths for the source and destination of pending copies from copy agent  108 . Table services  310  may send an acknowledgement to copy agent  108  whenever an address is added to or removed from the pending copy table stored in memory  304 .  
         [0034]     As introduced above, compare services  312  may provide control agent  104  with the ability to compare addresses within instructions to be executed with addresses stored in the pending copy table. In one example embodiment, compare services  312  may check the load and store addresses that the CPU generates when executing instructions.  
         [0035]     Stall services  314 , as introduced above, may provide control agent  104  with the ability to block the execution of load and store operations (and thereby the originating instructions) if the address within an instruction matches an address in the pending copy table. In one embodiment, stall services  314  will allow memory accesses to be retried periodically or after an entry has been removed from the pending copy table. In another embodiment, stall services  314  may provide an indication to processor(s)  102  that a particular instruction includes a memory address that should not be accessed, and processor(s)  102  may then stall the execution of the instruction.  
         [0036]      FIG. 4  is a flow chart of an example method for early copy completion, in accordance with one example embodiment of the invention. It will be readily apparent to those of ordinary skill in the art that although the following operations may be described as a sequential process, many of the operations may in fact be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged without departing from the spirit of embodiments of the invention.  
         [0037]     According to but one example implementation, method  400  begins when copy agent  108  may make ( 402 ) a copy globally observable. In one example embodiment, a DMA request may originate from one of processor(s)  102 , for example as part of a TCP/IP software stack or other application. Notify services  210  may send the buffer address and length to each of table services  310 , which would store the pending copy in a table in memory  304 .  
         [0038]     Next, copy agent  108  may notify ( 404 ) of copy completion before the copy is performed. In one example embodiment, notify services  210  will send the early copy completion notification after receiving acknowledgements from all processor(s)  102  that they are aware of the pending copy.  
         [0039]     Next, stall services  314  may stall ( 406 ) copy-dependent instructions. In one embodiment, compare services  312  looks the source and destination addresses of instructions to be executed up in the pending copy table. Stall services  314  may block those instructions where the instruction addresses match or overlap addresses in the pending copy table until the associated copy has been completed.  
         [0040]     At the same time, control logic  202  may selectively invoke copy services  212  to perform ( 408 ) the copy. In one example embodiment, copy services  212  copies at least a portion of a TCP/IP packet from one location in system memory  110  to another.  
         [0041]     Next, copy agent  108  may notify ( 410 ) of actual copy completion. In one embodiment, complete services  214  communicates to each of processor(s)  102  that the copy has actually completed.  
         [0042]     Next, control agent  104  may clear ( 412 ) tables associated with the copy. In one embodiment, table services  310  clears the associated entry from the pending copy table, thereby allowing any instruction that was blocked by stall services  314  as a result of the pending copy to be executed.  
         [0043]     In the description above, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details. In other instances, well-known structures and devices are shown in block diagram form.  
         [0044]     Embodiments of the present invention may be used in a variety of applications. Although the present invention is not limited in this respect, the invention disclosed herein may be used in microcontrollers, general-purpose microprocessors, Digital Signal Processors (DSPs), Reduced Instruction-Set Computing (RISC), Complex Instruction-Set Computing (CISC), among other electronic components. However, it should be understood that the scope of the present invention is not limited to these examples.  
         [0045]     The present invention includes various operations. The operations of the present invention may be performed by hardware components, or may be embodied in machine-executable content (e.g., instructions), which may be used to cause a general-purpose or special-purpose processor or logic circuits programmed with the instructions to perform the operations. Alternatively, the operations may be performed by a combination of hardware and software. Moreover, although the invention has been described in the context of a computing appliance, those skilled in the art will appreciate that such functionality may well be embodied in any of number of alternate embodiments such as, for example, integrated within a communication appliance (e.g., a cellular telephone).  
         [0046]     Many of the methods are described in their most basic form but operations can be added to or deleted from any of the methods and information can be added or subtracted from any of the described messages without departing from the basic scope of the present invention. Any number of variations of the inventive concept is anticipated within the scope and spirit of the present invention. In this regard, the particular illustrated example embodiments are not provided to limit the invention but merely to illustrate it. Thus, the scope of the present invention is not to be determined by the specific examples provided above but only by the plain language of the following claims.