Abstract:
Systems and methods for reducing problems and disadvantages associated with power consumption in memory devices are disclosed. A method for reducing power consumption in memory may include tracking, by an operating system executing on a processor, one or more logical units of a memory system that are in use. The method may also include setting, by the operating system, a variable indicating a portion of the memory system in use based on the logical units of the memory system in use. The method may additionally include refreshing one or more of the one or more logical units of the memory system based on the variable.

Description:
TECHNICAL FIELD 
     The present disclosure relates in general to reducing power consumption in information handling systems, and more particularly to reducing power consumption of memory. 
     BACKGROUND 
     As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems. 
     Information handling systems often use memory to store data and/or instructions. Broadly speaking, term memory refers to computer components, devices, and recording media that retain digital data used for processing for some interval of time. A commonly-used type of memory is known as dynamic random access memory (DRAM). DRAM is a type of random access memory that stores each bit (or cell) of data in a separate capacitive element within an integrated circuit. Because capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Such refreshing of DRAM cells consumes power. As the density and operating frequency of DRAMs increase, so too does the power consumed by DRAMs. Such consumption of power may lead to higher operating temperatures for the DRAMs and the information handling systems in which such DRAMs are present, which may affect operability of an information handling system and its components. In addition, such consumption of power may lead to higher operating costs due to increased energy costs associated with operation, as well as costs associated with cooling systems to mitigate increased temperatures. 
     SUMMARY 
     In accordance with the teachings of the present disclosure, the disadvantages and problems associated with power consumption in memory devices have been substantially reduced or eliminated. 
     In accordance with an embodiment of the present disclosure, a method for reducing power consumption in memory may include tracking, by an operating system executing on a processor, one or more logical units of a memory system that are in use. The method may also include setting, by the operating system, a variable indicating a portion of the memory system in use based on the logical units of the memory system in use. The method may also include refreshing one or more of the one or more logical units of the memory system based on the variable. 
     In accordance with another embodiment of the present disclosure, an information handling system may include a processor, a memory system communicatively coupled to the processor and having one or more logical units, and a computer-readable medium communicatively coupled to the processor and having stored thereon one or more executable instructions. The one or more executable instructions may be configured to, when executed by the processor: (i) track one or more logical units of a memory system that are in use; (ii) set a variable indicating a portion of the memory system in use based on the logical units of the memory system in use; and (iii) refresh one or more of the one or more logical units of the memory system based on the variable. 
     In accordance with a further embodiment of the present disclosure, a method for reducing power consumption in memory, may include issuing a command to refresh a particular logical unit of a memory to the exclusion of other logical units of the memory. 
     Other technical advantages will be apparent to those of ordinary skill in the art in view of the following specification, claims, and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein: 
         FIG. 1  illustrates a block diagram of an example information handling system incorporating partial memory refresh, in accordance with certain embodiments of the present disclosure; 
         FIGS. 2A and 2B  illustrate a flow chart of example methods for allocating and deallocating banks, in accordance with certain embodiments of the present disclosure; 
         FIG. 3  illustrates various fields associated with mode register MR 2  of a DRAM according to the JEDEC Specification, in accordance with certain embodiments of the present disclosure; 
         FIGS. 4A and 4B  illustrate a flow chart of example methods for executing reliability, availability, and serviceability (RAS) features in a memory module, in accordance with certain embodiments of the present disclosure; 
         FIG. 5A  illustrates a command format for a refresh command according to the JEDEC Specification, in accordance with certain embodiments of the present disclosure; 
         FIG. 5B  illustrates a command format for a modified refresh command, in accordance with certain embodiments of the present disclosure; and 
         FIG. 6  illustrates various fields associated with a mode register for use with a partial memory refresh command, in accordance with certain embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments and their advantages are best understood by reference to  FIGS. 1-6 , wherein like numbers are used to indicate like and corresponding parts. 
     For the purposes of this disclosure, an information handling system may include any instrumentality or aggregate of instrumentalities operable to compute, classify, process, transmit, receive, retrieve, originate, switch, store, display, manifest, detect, record, reproduce, handle, or utilize any form of information, intelligence, or data for business, scientific, control, entertainment, or other purposes. For example, an information handling system may be a personal computer, a PDA, a consumer electronic device, a network storage device, or any other suitable device and may vary in size, shape, performance, functionality, and price. The information handling system may include memory, one or more processing resources such as a central processing unit (CPU) or hardware or software control logic. Additional components or the information handling system may include one or more storage devices, one or more communications ports for communicating with external devices as well as various input and output (I/O) devices, such as a keyboard, a mouse, and a video display. The information handling system may also include one or more buses operable to transmit communication between the various hardware components. 
     For the purposes of this disclosure, computer-readable media may include any instrumentality or aggregation of instrumentalities that may retain data and/or instructions for a period of time. Computer-readable media may include, without limitation, storage media such as a direct access storage device (e.g., a hard disk drive or floppy disk), a sequential access storage device (e.g., a tape drive), compact disk, CD-ROM, DVD, random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), and/or flash memory; as well as communications media such wires, optical fibers, microwaves, radio waves, and other electromagnetic and/or optical carriers; and/or any combination of the foregoing. 
       FIG. 1  illustrates a block diagram of a an example information handling system  102  incorporating partial memory refresh, in accordance with certain embodiments of the present disclosure. In certain embodiments, information handling system  102  may comprise a computer chassis or enclosure (e.g., a server chassis holding one or more server blades). In other embodiments, information handling system  102  may be a personal computer (e.g., a desktop computer or a portable computer). As depicted in  FIG. 1 , information handling system  102  may include a processor  103 , a memory system  104  communicatively coupled to processor  103 , and a storage medium  106  communicatively coupled to processor  103 . 
     Processor  103  may include any system, device, or apparatus configured to interpret and/or execute program instructions and/or process data, and may include, without limitation a microprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), or any other digital or analog circuitry configured to interpret and/or execute program instructions and/or process data. In some embodiments, processor  103  may interpret and/or execute program instructions and/or process data stored and/or communicated by one or more of memory system  104 , storage medium  106 , and/or another component of information handling system  100 . 
     Memory system  104  may be communicatively coupled to processor  103  and may comprise any system, device, or apparatus operable to retain program instructions or data for a period of time (e.g., computer-readable media). Memory system  104  may comprise random access memory (RAM), electrically erasable programmable read-only memory (EEPROM), a PCMCIA card, flash memory, magnetic storage, opto-magnetic storage, or any suitable selection and/or array of volatile or non-volatile memory that retains data after power to information handling system  102  is turned off. In particular embodiments, memory system  104  may comprise dynamic random access memory (DRAM). 
     As shown in  FIG. 1 , memory system  104  may include memory controller  108 , one or more memory modules  116   a - 116   n  communicatively coupled to memory controller  108 , and status registers  112  communicatively coupled to memory controller  108 . Memory controller  108  may be any system, device, or apparatus configured to manage and/or control memory system  104 . For example, memory controller  108  may be configured to read data from and/or write data to memory modules  116  comprising memory system  104 . Additionally or alternatively, memory controller  108  may be configured to refresh memory modules in embodiments in which memory system  104  comprises DRAM. Although memory controller  108  is shown in  FIG. 1  as an integral component of memory system  104 , memory controller  108  may be separate from memory system  104  and/or may be an integral portion of another component of information handling system  102  (e.g., memory controller  108  may be integrated into processor  103 ). 
     Each memory module  116  may include any system, device or apparatus configured to retain program instructions and/or data for a period of time (e.g., computer-readable media). Each memory module  116  may include a dynamic random access memory (DRAM) module (e.g., a dual in-line package (DIP) memory, a Single In-line Pin Package (SIPP) memory, a Single Inline Memory Module (SIMM), a Ball Grid Array (BGA)), or any other suitable memory. 
     As depicted in  FIG. 1 , each memory module  116  may include one or more ranks  118   a - 118   m . Each memory rank  118  within a memory module  116  may be a block or area of data created using some or all of the memory capacity of the memory module  116 . In some embodiments, each rank  118  may be a rank as such term in defined by the Joint Electron Device Engineering Council (JEDEC) Standard for memory devices. 
     Also as shown in  FIG. 1 , each rank  118  may include mode registers  120  and one or more memory banks  110 . Each memory bank  110  may be a logical unit of storage within memory system  104 , which may be based on physical parameters of the memory module  116  comprising such memory bank  110 . 
     Mode registers  120  may include one or more configuration variables and/or parameters associated with memory system  104 . When reading, writing, refreshing, and/or performing other operations associated with memory system  104 , a memory module  116  may carry out such operations based at least in part on configuration parameters and/or variables stored in mode registers  120 . In some embodiments, mode registers  120  may be defined by a Joint Electron Device Engineering Council (JEDEC) standard for memory devices. 
     Status registers  112  may include one or more configuration variables and/or parameters associated with memory system  104 . When reading, writing, refreshing, and/or performing other operations associated with memory system  104 , memory controller  108  may carry out such operations based at least in part on configuration parameters and/or variables stored in status registers  112 . In some embodiments, status registers  112  may include registers similar to mode registers  120 . 
     Storage medium  106  may be communicatively coupled to processor  104 . Storage medium  106  may include any system, device, or apparatus operable to store information processed by processor  103 . Storage medium  106  may include, for example, network attached storage, one or more direct access storage devices (e.g. hard disk drives), and/or one or more sequential access storage devices (e.g. tape drives). As shown in  FIG. 1 , storage medium  106  may have stored thereon an operating system (OS)  114 . OS  114  may be any program of executable instructions, or aggregation of programs of executable instructions, configured to manage and/or control the allocation and usage of hardware resources such as memory, CPU time, disk space, and input and output devices, and provide an interface between such hardware resources and application programs hosted by OS  114 . Active portions of OS  114  may be transferred to memory  104  for execution by processor  103 . 
     In operation, processor  103  and/or memory controller  108  may manage and control the various banks  110  such that memory refresh operations may be executed with respect to one or more of banks  110 , as described in greater detail below. In some embodiments, some, but not all of the banks  110  will be refreshed, thus decreasing the power consumed in connection with refresh operations as compared to traditional approaches. Examples of such embodiments are described below. 
     Example Embodiment 1 
     In accordance with an example embodiment of the present disclosure, partial memory refresh may be implemented with minimal or no change to traditional memory controllers and/or JEDEC Specifications, and may be implemented mainly within OS  114 . In this embodiment, OS  114  may be configured to, when executed by processor  103 , disable bank-level interleaving, and/or any reliability, availability, and serviceability (RAS) features of memory controller  108  (e.g., patrol scrubbing, sparing, mirroring, etc.), which might force multiple partially occupied banks to stay active or generate false error conditions. OS  114  may further be enabled to, when allocating and/or de-allocating memory, track such memory allocation on a per rank and/or per bank basis (e.g., by storing variables and/or parameters indicative of such usage in status registers  112  or other suitable medium). As memory is allocated and/or de-allocated, OS  114  may update variables and/or parameters stored in status registers  112  indicative of the usage of the various banks  110 . In addition, OS  114  may alter the contents of a mode register to indicate a fraction of the memory being used. As a particular example, mode register MR 2 , as defined by the JEDEC Specification, may be modified by OS  114  to indicate usage of banks  110 . 
     As OS  114  invokes and terminates programs executing on processor  103 , it may attempt to allocate and de-allocate memory so as to fill active banks  110  before allocating additional banks  110 , thus keeping the number of active banks  110  at a minimum. 
       FIG. 2A  illustrates a flow chart of an example method  150  for allocating banks  110 , in accordance with certain embodiments of the present disclosure. According to one embodiment, method  150  may begin at step  152 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of information handling system  102 . As such, the initialization point for method  150  and the order of the steps  152 - 164  comprising method  150  may depend on the implementation chosen. 
     At step  152 , operating system  114 , which may have been loaded into memory  104 , may begin the process of allocating a page of memory to a program. At step  154 , processor  103 , memory controller  108 , or another component of information handling system  102  may determine if space is available in a presently active bank  110  in a memory module  116  for storage of the allocated page. In some embodiments, such determination may be made by reference to parameters stored in status registers  112 , mode registers  120 , and/or another component of information handling system  102 . If space in available in an active bank  110 , method  150  may proceed to step  156 . Otherwise, method  150  may proceed to step  158 . 
     At step  156 , in response to a determination that space is available in a presently active bank  110 , processor  103 , memory controller  108 , and/or another component of information handling system  102  may allocate the page to space in an active bank  110 . After completion of step  154 , method  150  may end. 
     At step  158 , in response to a determination that space is not available in a presently active bank  110 , processor  103 , memory controller  108 , and/or another component of information handling system  102  may select a presently idle bank  110  to be made active. At step  160 , a mode register  120  may be updated to indicate that the idle bank  110  is to become an active bank  110 . At step  162 , memory controller  108  may clear the idle bank  110 . At step  164 , memory controller  108  may allocate the page to the formerly idle/now active bank  110 . 
     Although  FIG. 2A  discloses a particular number of steps to be taken with respect to method  150 , method  150  may be executed with greater or lesser steps than those depicted in  FIG. 2A . In addition, although  FIG. 2A  discloses a certain order of steps to be taken with respect to method  150 , the steps comprising method  150  may be completed in any suitable order. 
     Method  150  may be implemented using information handling system  102  or any other system operable to implement method  150 . In certain embodiments, method  150  may be implemented partially or fully in software and/or firmware embodied in computer-readable media. 
       FIG. 2B  illustrates a flow chart of an example method  180  for deallocating banks  110 , in accordance with certain embodiments of the present disclosure. According to one embodiment, method  180  may begin at step  182 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of information handling system  102 . As such, the initialization point for method  180  and the order of the steps  182 - 186  comprising method  180  may depend on the implementation chosen. 
     Beginning at step  182 , operating system  114  may deallocate a page from a bank  110 . At step  184 , processor  103 , memory controller  108 , or another component of information handling system  102  may determine if all pages within the bank  110  comprising the deallocated page are idle. In some embodiments, such determination may be made by reference to parameters stored in status registers  112 , mode registers  120 , and/or another component of information handling system  102 . If all pages are idle, method  180  may proceed to step  186 . Otherwise, method  180  may end. 
     At step  186 , in response to a determination that all pages within the bank  110  comprising the deallocated page are idle, a mode register  120  may be updated to indicate that the bank  110  has become idle. After completion of step  186 , method  180  may end. 
     Although  FIG. 2B  discloses a particular number of steps to be taken with respect to method  180 , method  180  may be executed with greater or lesser steps than those depicted in  FIG. 2B . In addition, although  FIG. 2B  discloses a certain order of steps to be taken with respect to method  180 , the steps comprising method  180  may be completed in any suitable order. 
     Method  180  may be implemented using information handling system  102  or any other system operable to implement method  180 . In certain embodiments, method  180  may be implemented partially or fully in software and/or firmware embodied in computer-readable media. 
       FIG. 3  illustrates various fields associated with mode register MR 2  of a DRAM according to the JEDEC Specification, in accordance with certain embodiments of the present disclosure. As shown in  FIG. 3 , mode register MR 2  includes a three-bit field labeled as PASR or “Partial Array Self-Refresh.” By appropriately setting this field as memory pages and banks  110  are allocated and deallocated in accordance with the methods described above with respect to  FIGS. 2A and 2B , such PASR field may indicate to memory controller  108  a fraction (e.g., one-eighth, one-fourth, one-half, three-fourths, all) of the banks  110  that are in use. Accordingly, during self-refresh, only a portion of the memory banks  110 , as indicated by the PASR field, may be refreshed, which may reduce power consumption associated with refresh as compared to traditional approaches. 
     Example Embodiment 2 
     In accordance with another example embodiment of the present disclosure, partial memory refresh may be implemented with minimal change to traditional memory controllers and/or little or minimal change to JEDEC Specifications. In this embodiment, OS  114  may be configured to, when executed by processor  103 , disable bank-level interleaving. OS  114  may further be enabled to, when allocating and/or de-allocating memory, track such memory allocation on a per rank and/or per bank basis (e.g., by storing variables and/or parameters indicative of such usage in status registers  112  or other suitable medium). As memory is allocated and/or de-allocated, memory controller  108  may update variables and/or parameters stored in status registers  112  indicative of the usage of the various banks  110 . For example, memory controller  108  may be configured to track a bank-in-use status of each bank  110 . Such bank-in-use information may be stored in status registers  112  or another suitable medium. As the bank-in-use status is updated as banks  110  are allocated and de-allocated, memory controller  108  may also alter contents of a mode register (e.g., mode register MR 2 , as described above with respect to Example Embodiment 1) to indicate usage of banks  110  in according with the existing JEDEC Specification. Accordingly, during self-refresh, only a portion of the memory banks  110 , as indicated by the PASR field, may be refreshed, which may reduce power consumption associated with refresh as compared to traditional approaches. 
     In Example Embodiment 2, RAS features of memory controller  108  (e.g., patrol scrubbing, sparing, mirroring, etc.) may be enabled, and memory controller  110  may check the bank-in-use status of each bank  110  before performing such RAS operation, such as depicted in  FIGS. 4A and 4B  below. 
       FIG. 4A  illustrates a flow chart of an example method  400  for executing certain reliability, availability, and serviceability (RAS) features in a memory module  116 , in accordance with certain embodiments of the present disclosure. According to one embodiment, method  400  may begin at step  402 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of information handling system  102 . As such, the initialization point for method  400  and the order of the steps  402 - 412  comprising method  400  may depend on the implementation chosen. 
     At step  402 , a spare DIMM, spare rank, spare channel, or re-silvering operation may be required by memory controller  108 . At step  404 , processor  103 , memory controller  108 , and/or another component of information handling system  102  may determine if all memory cache lines responsive to the required RAS operation have been copied. If it is determined that all memory cache lines responsive to the required RAS operation have been copied, method  400  may end. Otherwise, method  400  may proceed to step  406 . 
     At step  406 , in response to a determination that not all memory cache lines responsive to the required RAS operation have been copied, processor  103 , memory controller  108 , and/or another component of information handling system may determine the bank status of the current cacheline. The bank status may include whether or not the current cacheline is associated with a bank  110  that is presently valid (e.g., presently allocated or active). At step  408 , if it is determined that the bank  110  associated with the cacheline is valid, method  400  may proceed to step  410 . Otherwise, method  400  may proceed to step  412 . 
     At step  410 , in response to a determination that a the bank  110  associated with the current cacheline is valid, the cacheline may be written to the spare location. 
     At step  412 , a counter may be incremented to indicate that the next cacheline should next be processed in accordance with the steps above. After completion of step  412 , method  400  may proceed again to step  404 . 
     Although  FIG. 4A  discloses a particular number of steps to be taken with respect to method  400 , method  400  may be executed with greater or lesser steps than those depicted in  FIG. 4A . In addition, although  FIG. 4A  discloses a certain order of steps to be taken with respect to method  400 , the steps comprising method  400  may be completed in any suitable order. 
     Method  400  may be implemented using information handling system  102  or any other system operable to implement method  400 . In certain embodiments, method  400  may be implemented partially or fully in software and/or firmware embodied in computer-readable media. 
       FIG. 4B  illustrates a flow chart of an example method  450  for executing a patrol scrub in a memory module  116 , in accordance with certain embodiments of the present disclosure. According to one embodiment, method  450  may begin at step  452 . As noted above, teachings of the present disclosure may be implemented in a variety of configurations of information handling system  102 . As such, the initialization point for method  450  and the order of the steps  452 - 460  comprising method  450  may depend on the implementation chosen. 
     At step  452 , a patrol scrub operation may be required by memory controller  108 . At step  454 , processor  103 , memory controller  108 , and/or another component of information handling system may determine whether the bank  110  associated with the patrol scrub operation is presently valid (e.g., presently allocated or active). If it is determined that the bank  110  is valid, method  450  may proceed to step  456 . Otherwise, method  450  may end. 
     At step  456 , processor  103 , memory controller  108 , and/or another component of information handling system may read the memory location associated with the patrol scrub operation. At step  458 , processor  103 , memory controller  108 , and/or another component of information handling system may determine whether or not an error correction code (ECC) associated with the memory location is valid. If it is determined that the ECC is not valid, method  450  may proceed to step  460 . Otherwise, method  450  may end. 
     At step  460 , in response to a determination that the ECC is not valid, the ECC may be fixed and corrected data may be written back to the memory location. 
     Although  FIG. 4B  discloses a particular number of steps to be taken with respect to method  450 , method  450  may be executed with greater or lesser steps than those depicted in  FIG. 4B . In addition, although  FIG. 4B  discloses a certain order of steps to be taken with respect to method  450 , the steps comprising method  450  may be completed in any suitable order. 
     Method  450  may be implemented using information handling system  102  or any other system operable to implement method  450 . In certain embodiments, method  450  may be implemented partially or fully in software and/or firmware embodied in computer-readable media. 
     Example Embodiment 3 
     Example Embodiment 3 may be similar to Example Embodiment 2, except that Example Embodiment 3 defines an enhancement to a command present in traditional approaches. For example, the REFRESH command protocol of the JEDEC Specification may be enhanced to enable partial memory refresh. 
       FIG. 5A  illustrates a command format for a REFRESH command according to the JEDEC Specification. In accordance with the JEDEC Specification, a REFRESH command, known as a “direct” refresh, may cause refresh to occur in a bank  110  of a memory module  116  determined by the memory module  116 . Notably, the BA3:0 field is not presently used by the REFRESH command. However, this field of the traditional REFRESH command may be used to indicate a specific bank to be refreshed pursuant to a direct refresh command. For example, as shown in  FIG. 5B , in an eight-bank memory, the JEDEC standard REFRESH command may be modified such that field BA2:0 may be used to indicate the bank to be refreshed. Accordingly, Example Embodiment 3 adds partial memory direct refresh to the partial self-refresh functionality described in Example Embodiments 1 and 2. 
     Example Embodiment 4 
     Example Embodiment 4 may be similar to Example Embodiment 3, except that Example Embodiment 4 defines a new data register. For example, Example Embodiment 4 may define a new JEDEC mode register, as shown in  FIG. 4 . The new mode register may include a bit for each bank  110 . Accordingly, this new register allows for arbitrary enabling and disabling for each bank  110 , as compared to the more rigid groupings supported by the standard PASR field of mode register MR 2 , as described above. Thus, during self-refresh, a portion of the memory banks  110 , as indicated by the new mode register, may be refreshed, which may reduce power consumption associated with refresh as compared to traditional approaches. 
     Although the present disclosure has been described in detail, it should be understood that various changes, substitutions, and alterations can be made hereto without departing from the spirit and the scope of the disclosure as defined by the appended claims. As a specific example, although the embodiments above describe enabling refresh on a per bank basis for the purposes of simplicity and exposition, any appropriate level of granularity, whether a larger or smaller granularity than a bank, may be used.