Abstract:
An exemplary method controls the loading of a program in a computer system using a disk based operating system instead of allowing a built-in loading program resident in the operating system to handle the loading. The method separates the loading of the program into a series of modules that are loaded from a disk into random access memory where each module has a predefined target time interval within which the loading of the module is to be completed. The computer system is released to process other tasks following completion of the loading of one module and before the start of loading of a following module so that disruptions to the processing of the other tasks running on the computer system are minimized.

Description:
BACKGROUND  
       [0001]     This invention generally relates to computer systems using disk based computer operating systems and more specifically addresses the loading of a program stored on a disk into memory of a computer system.  
         [0002]     Several different disk based operating systems are in use in computer systems. For example, Microsoft Windows XP and UNIX are disk based operating systems that are utilized in a large number of computer systems. Other disk based operating systems are in use or have been utilized in computer systems that are no longer being produced.  
         [0003]      FIG. 1  illustrates an exemplary computer system  10  that includes a computer  12  that is supported by peripherals such as monitor  14  and keyboard  16 . Computer  12  is also linked to external network  18  such as by known communication protocols, e.g. Ethernet or a form of Internet Protocol. The computer  12  includes one or more microprocessors  20  that are supported by read-only memory (ROM)  22 , random access memory (RAM)  24 , and hard disk  26 . This computer  12  can be used in a configuration where hard disk  26  does not exist and is replaced by disk  25  accessed via external network  18  with the assistance of a remote server or computer  27 . An input/output (I/O) interface  28  supports communications between the microprocessor  20  and the external environment. The ROM  22  contains nonvolatile instructions such as are commonly read during the initial boot startup of the microprocessor  20 . The RAM  24  supports various operational code and data utilized by the microprocessor  20  during the execution of a plurality of programs and tasks. Hard drive  26  provides nonvolatile storage of various programs and data, and typically provides for a substantial amount of storage that commonly exceeds the storage capacity of RAM  24 . During the initial boot startup, basic instructions are typically fetched from ROM  22  and the hard disk that enables the processor  20  to load programs and data stored in the hard disk  26  into RAM  24  from which such programs are executed by the microprocessor  20 .  
         [0004]      FIG. 2  is an exemplary flow diagram illustrating how a microprocessor utilizing a UNIX disk based operating system typically processes requests for service, e.g. a request to load a program stored on the hard disk. In step  30  the microprocessor receives a request for service that may be initiated by a system call or an interrupt. A determination is made in step  32  of whether the request requires real-time processing. A NO determination by step  32  results in the request being granted a quantum of time (or time equivalents such as a predetermined number of cycles) to proceed with a task associated with the request in step  34 . In step  36  a determination is made of whether the quantum has elapsed or the task has completed. A NO determination by step  36  results in processing returning to the beginning of step  36 . A YES determination by step  36  results in the termination of the current processing at step  38 . In step  40  the microprocessor is released to go to the next request. If the YES determination in step  36  was caused by the task having been completed, then the associated request for service is satisfied and no further processing requests associated with this completed task are required and hence no additional or supplemental requests will be put in a queue to cause additional processing by the microprocessor. If the YES determination step  36  was caused by the quantum time having elapsed, then the task associated with the request has not been completed and a supplemental request will be put in a queue to be acted upon by the microprocessor when the supplemental request is reached by the microprocessor. This permits a task requiring longer than the quantum time to be completed in a time multiplexed manner along with other tasks and operations required to be performed by the microprocessor.  
         [0005]     A YES determination by step  32  indicates that real-time processing of the associated task is required. In accordance with real-time processing requirements, the processing of the real-time task is started as indicated in step  42 . In step  44  a determination is made of whether the task is completed. A NO determination by step  44  results in processing continuing to the beginning of the step, i.e. the processing of the task continues. A YES determination by step  44  indicates that the task has been completed and the microprocessor is released from the processing of this task as indicated by step  40 . Since the microprocessor continues to process a real-time process request until it is completed, this means that the processing of other requests and tasks by the microprocessor is deferred for the time interval required to conclude the processing of the currently running real-time task.  
         [0006]     The processing of some real-time tasks in the disk based operating system computer environment explained with regard to  FIG. 2  can present difficulties especially where other time critical requests or tasks are waiting to be started or for further processing. For example, a real-time request to load a new program of a substantial size, e.g. 10 Megabytes, from the disk operating system may require a substantial amount of processing time, e.g. several seconds. Since other programs and tasks will not be able to obtain processing from the microprocessor during this time, some waiting programs or tasks may result in a fault or failure due to a time critical need for processing that was not met. Thus, there exists a need to prevent tasks from excessively monopolizing the processing capability of the microprocessor to the detriment of other tasks, especially but not limited to, loading a program from a hard drive into RAM memory.  
       SUMMARY  
       [0007]     It is an object of the present invention to minimize difficulties associated with this problem.  
         [0008]     An exemplary method controls the loading of a program in a computer system using a disk based operating system instead of allowing a built-in loading program resident in the operating system to handle the loading. The method separates the loading of the program into a series of modules that are loaded from a disk into random access memory where each module has a predefined target time interval within which the loading of the module is to be completed. The computer system is released to process other tasks following completion of the loading of one module and before the start of loading of a following module so that disruptions to the processing of the other tasks running on the computer system are minimized.  
         [0009]     An exemplary computer system and an article including one or more computer-readable signal-bearing media are also presented. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  illustrates an exemplary computer system known in the art.  
         [0011]      FIG. 2  illustrates an exemplary flow diagram of steps known in the art for servicing a request in a computer system.  
         [0012]      FIG. 3  is a flow diagram of an exemplary method for determining a threshold time in accordance with an embodiment of the present invention.  
         [0013]      FIG. 4  is a flow diagram of another exemplary method in accordance with the present invention for controlling the time a microprocessor is occupied with carrying out a requested task.  
         [0014]      FIG. 5  is a flow diagram of an embodiment further illustrating exemplary steps for implementing step  90  as shown in  FIG. 4 . 
     
    
     DETAILED DESCRIPTION  
       [0015]     The exemplary embodiment of the present invention will be described for use on a computing system with a disk based UNIX operating system such as available from Hewlett-Packard and Solaris. However, it will be understood that other computing systems with disk based operating systems that have similar needs can also benefit. This embodiment is especially, but not exclusively, adapted for controlling the loading of an executable program stored on the hard disk into memory where the operating system, without the benefit of the present embodiment, would normally cause the entire program to be loaded in one continuous, uninterrupted, processing task by the microprocessor. In accordance with the embodiment of the present invention, an executable program that requires longer than a predetermined time to be loaded from a hard disk into memory is automatically loaded as time separated modules so that the microprocessor can attend to other tasks between the loading of the modules. As the modules are loaded, the number of pages loaded into memory is preferably automatically adjusted to maximize the number of pages that can be loaded during the targeted time allotted for loading of each module.  
         [0016]      FIG. 3  is a flow diagram of steps in an exemplary method in accordance with the present invention for determining a target time interval (loading threshold—LT) that will be allocated to the loading of each module of the program to be loaded. The steps in  FIG. 3  are preferably executed from a call placed in the computer system startup scripts at a point where the computer system executes only 1 task at a time (single user mode) prior to entering a mode where a plurality of tasks are executed (multi-user mode). In step  50  variable N is set equal to 1. In step  52  a wall clock time is measured and stored as T 1 . As used herein a “wall clock time” refers to a time measured on a running chronological clock that is preferably of high accuracy. The time may be represented as a conventional time measurement based on hours, minutes, seconds, etc. or maybe represented by a number representative of an instant of time. In step  54  the microprocessor causes 25 pages to be read from the disk drive via an application page fault, loaded and locked into RAM memory. In the illustrative example, work is denominated in terms of pages, where a typical page size might be 8192 or 65536 bytes. Information is read and loaded on a page basis. Causing a page to be read into memory from disk for purposes of this embodiment is hereafter referred to as application page faulting. It is only necessary to request the operating system to read one byte at a memory address contained within the page. This read causes a page fault (a default operating system action where the operating system transfers all bytes contained in the page from the disk into memory) of the entire page into memory. The operating system uses the memory map established for the executing instance of the executable program to understand the location of the bytes on disk vis-à-vis the location of the bytes in memory. As used herein to “lock” a page in memory means to prevent information loaded into the page from being swapped from memory back to the hard disk. In step  56  the wall clock time is again measured and stored as T 2 . In step  58  the elapsed time between T 2  and T 1  is stored in memory. This elapsed time represents the cumulative time required to access, load and lock 25 pages into RAM memory from the hard disk. If the information to be loaded into RAM memory in a local computing system is resident on a hard drive or other data storage device located in an external network, delays in the communication links between the computing system and the data storage device in the external network is included in the measured elapsed time.  
         [0017]     In step  60  a determination is made of whether N is less than 100. A YES determination by step  60  results in step  62  incrementing N, i.e. N=N+1. Control then returns to the input of step  52  where another elapsed time measurement will be made. A NO determination by step  60  represents that 100 such elapsed time measurements have been made and results in step  64  averaging the stored elapsed time measurements resulting in the calculation of an average elapsed time. This average elapsed time is preferably multiplied by 1.5 or some other linear scalar. (This elapsed time is preferably calculated when the computer system is running only one task. When the computer system is later running a plurality of tasks, some additional overhead must be planned into the threshold). In step  66  a load threshold (LT) time interval is stored and is based on the average elapsed time multiplied by the linear scalar. Depending upon the specific application and computing environment, the LT time interval that is selected should be an acceptable, uninterruptible processing interval. The actual LT time interval calculated via  FIG. 3  is based on the average elapsed time, and factors in the speed of the subject microprocessor, memory latency, and disk latency. It will be understood that amounts of memory other than 25 pages and other than 100 elapsed time measurements can be utilized. The specific amount of memory to be fetched and the number of elapsed time measurements to be made can be advantageously selected to better reflect differing capabilities of various computer systems.  
         [0018]     An alternative to the method described in  FIG. 3  would be to manually select a time interval and manually store the selected time interval at a memory location or in a system accessible variable. However, such a manual derivation of a target time interval would not benefit from testing the actual system to be used and hence may not accurately account for time delays experienced by the computer system. System/program requirements that may specify maximum time intervals within which certain tasks must be completed may override the calculated LT value. The LT value is preferably not larger than 50% of such a required maximum time interval. In such a case, it may be desirable to manually select the interval.  
         [0019]      FIG. 4  is a flow diagram of an exemplary method for controlling the time a microprocessor is occupied with carry out a requested task. The exemplary method effectively interposes a load control function ahead of the normal load control function embedded in the disk based operating system in order to more effectively control the loading of an executable program from hard disk into RAM memory as a series of modules. In the illustrative example the operating system is a disk based UNIX operating system which would, without the benefit of the exemplary embodiment, react to a request to load an executable program in a real-time environment by causing a continuous, uninterruptible loading of the executable program until the complete executable program was loaded.  
         [0020]     Step  80  represents a microprocessor that is processing a plurality of tasks. In step  82  new task requests are monitored, i.e. the presence of a request to be presented to the microprocessor to initiate a new task such as loading an executable program is detected. For example, this may comprise monitoring for specific types of system calls associated with the loading of an executable program in the UNIX disk based operating system. This invention can best be implemented by interposing the UNIX init call immediately prior to init calling Static Constructors. This invention can also be interposed on the command to map a new range of memory sometimes called mmap to handle startup loading or later dynamic creation or mapping of large memory blocks. In step  84  a determination is made of whether a new task has been requested. A NO determination by step  84  results in processing returning to the beginning of step  82 . A YES determination by step  84  means that a new task has been requested and results in step  86  making a determination of whether the type of task requires load management. For example, a load request of an executable program in a real-time environment would be one type of request requiring load management. Also, a request to load certain non-real-time executable programs may require load management where such programs have a large memory footprint and are loaded from remote disks accessed via an external network as shown in  FIG. 1  via network  18  from disk  25  through the help of computer  27 . Even though requests from a non-real-time executable are run at non-real-time, low-level tasks caused by such requests, i.e. transferring data from disk to memory, executed via hardware interrupts will delay even real-time tasks. A NO determination by step  86  results in step  88  causing the normal operating system load procedure to be used in response to the request. The processing is then returned to the beginning of step  82  to await a new task being requested.  
         [0021]     A YES determination by step  86  indicates a task has been requested that requires load management. This results in step  90  causing a pre-load library and an associated load managing function contained in a load management program to be loaded. Step  90  as discussed in greater detail with regard to  FIG. 5 . In step  92  a determination is made of whether the loading of the new task (executable program) is complete. A NO determination by step  92  results in control returning to step  90  to continue management of the loading. A YES determination by step  92  results in processing continuing to the input of step  82 .  
         [0022]      FIG. 5  is a flow diagram showing exemplary steps for implementing step  90  of  FIG. 4 . In step  100  a pre-load library is loaded such as by using the UNIX command “LD_PRELOAD_LIBRARY”. This action is taken at the beginning of execution of a request to run an executable program. After the executable program starts to run, this instance of the executable will be known as a process. The process of  FIG. 5  interposes itself as the program starts to run. The UNIX operating system only loads a small part of the executable program into memory. Additional pieces of the program will be loaded when they are needed by the program. When each additional piece is needed, the program will be delayed while the piece is read from disk. This invention interposes itself into the startup of the executable process before initial pieces of the executable program are loaded from hard disk into RAM memory.  
         [0023]     In step  102  the process memory map associated with the executable program that is starting up is read in order to obtain a map of memory (pages) from which the executable program is to be loaded or mapped into memory. This memory map information is provided as part of the UNIX operating system functionality. The page at which the loading is to begin is identified (the lowest memory address range in the map). During the initial startup the first set of pages (first module), the address of the page at which loading of information is to begin is also provided as part of the memory map information. The UNIX process memory map contains a table in which each row shows a beginning memory address, the amount of memory and a label identifying the type of program module to be loaded at this location. In step  104  a variable P is set to a default value, e.g. 100 pages, at the initial loading of the executable program into RAM memory. In step  106  a wall clock is read and stored as variable T 5 . In step  108  “P” pages of information are application page faulted from the hard disk, causing them to be stored in RAM memory at the memory address read from the memory map, and locked. A determination is made in step  110  of whether the entire executable program, i.e. the entire set of memory mapped address ranges, has been loaded. A YES determination by step  110  results in the processing terminating as indicated at END step  112 .  
         [0024]     A NO determination by step  110  results in the reading of the wall clock which is stored as variable T 6 . In step  116  a page capacity calculation is made based on LT−(T 6 −T 5 ) where LT is the target load threshold time interval and (T 6 −T 5 ) represents the time interval required to application page fault and lock the P pages into RAM memory. This is generally intended to refer to a comparison of these two time intervals and is not limited to the specific mathematical expression shown. If there is a positive value when the difference between these two time intervals is subtracted from LT representing the time to process the number of pages P, a calculation is made to determine an amount of pages Q that could be added to P for future iterations. For example, Q can be calculated using a linear interpolation. A positive value of Q indicates that additional pages can be processed during LT. For Example if (T 6 −T 5 ) took less than LT, a Q value is created that is set to 10% of P. Step  116  then sets P equal to a new value: P+Q, where this new value of pages P to be processed is stored for use during the next load iteration (next module) of the subject executable program. If there is a negative value from LT−(T 6 −T 5 ), it is necessary to pause the processing of pages for some amount of time S. For example S could be set equal to the absolute value of (LT−(T 6 −T 5 )) *5. To “pause” means that an operating system provided call such as sleep is used. This means that a timer is established with duration S and is entered into the operating system&#39;s timer queue. The program then voluntarily gives up the microprocessor and stops running. When the microprocessor is given up, the computer system is free to run any other of its plurality of tasks. When the timer expires, the program starts running again. In step  118  the identity of the last processed page is stored in memory and is used by step  102  during the next iteration to assist in determining the next page to be processed prior to issuing the sleep. A determination is made is step  120  of whether S&gt;0, i.e. if a pause is to be executed. A NO determination at step  120  causes processing to return to step  102  for processing of more modules. A YES determination at step  120  results in a sleep (pause) command to be issued in step  122 . Following the sleep interval in which the microprocessor works on other tasks, processing resumes at step  102  for processing of more modules.  
         [0025]     Although embodiments of the invention have been described above and shown in the drawings, various changes, additions and deletions can be made by those skilled in the art without departing from the spirit of the invention. For example, techniques other than wall clock time measurements are known for determining a time interval. It may be desirable to utilize the subject modular program loading technique for non-real-time program loading requests such as where an exceptionally large program is to be loaded or where other tasks are being processed that place constraints on the maximum time that can elapse before the resumption of such processing. RAM is intended to include all types of memory from which a microprocessor can directly execute programs. Hard disk and disk include all forms of information storage from which information must be first transferred to RAM before a microprocessor can execute it. Although the illustrative embodiment is explained in a computer system using a UNIX disk based operating system, those skilled in the art will appreciate that other disk based operating systems could also benefit. The scope of the present invention is defined by the following claims.