Abstract:
This present invention provides a portable user space application release/reacquire of adapter resources for a given job on a node using information in a network resource table. The information in the network resource table is obtained when a user space application is loaded by some resource manager. The present invention provides a portable solution that will work for any interconnect where adapter resources need to be freed and reacquired without having to write a specific function in the device driver. In the present invention, the preemption request is done on a job basis using a key or “job key” that was previously loaded when the user space application or job originally requested the adapter resources. This is done for each OS instance where the job is run.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTS 
     This invention was made with government support under subcontract HR0011-07-9-0002 awarded by DARPA. The Government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of scheduling jobs in a computing environment, and more particularly relates to scheduling jobs across multiple processors in a parallel computing system. 
     BACKGROUND OF THE INVENTION 
     A parallel application (also referred to task parallelism or function parallelism) is a form of parallelization of computer code across multiple processors in parallel computing systems. Task parallelism focuses on distributing execution processes (tasks or threads) across different parallel computing nodes. Scheduling techniques are used to schedule computer jobs in a parallel computing system so that the resources of the environment are efficiently utilized. 
     Traditionally, resource bookkeeping is buried at the lowest levels of the job scheduling logic, making it difficult and time consuming to extend existing job scheduling algorithms with novel paradigms, such as backfill and preemption. Resource bookkeeping is the tracking of used, free, bad, and to-be-used resources in the job scheduling algorithm. With current job scheduling algorithms, which allow a large variety of scheduling options, such as scheduling by hostlist, blocking, packing, etc., trying to extend the existing algorithms to support new, moderately complex scheduling paradigms, and at the same time maintain correctness of the current options, often requires substantial re-coding modifications to most of the underlying options. Typically, most of the currently supported scheduling options must also be supported by the new paradigms. As a result, introduction of new paradigms has a substantial impact on the existing code base. Development and testing cycles along with product quality are thus greatly effected. 
     One prior method used across multiple processors in a parallel computing system is a callback mechanism in the device drive (kernel space). The callback mechanism is implemented on a per thread/resource basis and was not portable. Therefore migrating from AIX to Linux requires extensive re-coding. Further this callback method is prone to timing errors. In order to properly handle these timing errors, the driver has to be recoded to provide stable and reliable preemption support. This delays development support for user space application preemption until driver can be recoded. The need to create customized code can be expensive and time consuming. 
     Resource scheduling can also be further complicated if the hardware in the parallel computing systems hardware in which the resource scheduler manages and/or the software for the resource scheduler changes. Again, preempting tasks running on each OS today requires customized programs that communicate with the scheduler. Development time, costs, and product quality are hence greatly impacted. 
     Therefore a need exists to overcome the problems with the prior art as discussed above. 
     SUMMARY OF THE INVENTION 
     The present invention provides a portable and non intrusive method for preemption support for any user space application running over interconnects that needs to free and re-obtain resources, such as adapter resources, associated with running over the interconnects. 
     This present invention provides a portable user space application release/reacquire of adapter resources for a given job on a computing node (or simply node) in a parallel computing system using information in a network resource table. The information in the network resource table is obtained when a user space application is loaded by a resource manager/load leveler. The present invention provides a portable solution that will work for any interconnect where adapter resources need to be freed and reacquired without having to write a specific function in the device driver. In the present invention, the preemption request is done on a job basis using a key or “job key” that was previously loaded when the user space application or job originally requested the adapter resources. This is done for each OS instance where the job is run. 
     In one embodiment the present invention is implemented as a daemon application that is providing this service is called Protocol Network Services Daemon (PNSD). It loads and unloads network adapter resources through Network Resource Table (NRT) APIs. The NRT APIs have been extended to provide preemption support: nrt_preemptjob( ) nrt_resumejob( ) nrt_query_preemption_state( ). 
     Preempt and resume calls are done on a job basis per OS instance. This way, the resource manager requires less tracking. The present invention provides managing preemption at each OS instance versus on a per process level. This is important in managing preemption of user space applications across multiple processors in a parallel computing system with a large number of CPUs and/or cores. For example in the IBM Power Parallel System the CPU count can be as large as 64. Having to manage just 1000 OS instance versus managing 64000 threads for preemption status is very critical in having an efficient preemption/resume capability. 
     The present invention is implemented as a system, a method, and a computer readable medium for managing preemption of a parallel application. The method executes on a computing node in a parallel computing system. The method begins by receiving, from a scheduler, a request with a key for managing preemption of a parallel application with a plurality of tasks running on at least one computing node in a multi-processor system as part of a parallel computing system, wherein the key has been previously associated to the parallel application. Next, using the key, a network resource table is accessed to retrieve all address locations of tasks associated with the application. The method collects a status for the tasks associated with the application by completing the following: i) sending a request to each of the tasks; and ii) storing at least one status entry for each of the tasks in a status table based on a type of reply received from each of the tasks. A reply is sent to the scheduler with an overall status of the application in response to the status entry for each of the tasks in the status table. 
     In one embodiment, the address locations of both nodes and adapters in the parallel computing system are retrieved from the network resource table. The status for each of the tasks associated with the application is stored. 
     In one embodiment the request from a scheduler is for preempting the parallel application and the reply is sent to the scheduler includes the overall status to indicate one of preempted, preempt_failed, and preempt_in_progress. 
     In another embodiment the request from the scheduler is for resuming the parallel application and the reply is sent to the scheduler includes the overall status to indicate one of resumed; resumed_failed; resume_in_progress. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying figures where like reference numerals refer to identical or functionally similar elements throughout the separate views, and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention, in which: 
         FIG. 1  is a diagram illustrating an example parallel computing system; 
         FIG. 2  is a diagram illustrates an example communication protocol stack operating on a processor of a parallel computing system such as that shown in  FIG. 1 ; 
         FIG. 3  illustrates an example network resource table operating for a processor such as that shown in  FIG. 2 ; 
         FIG. 4  illustrates an example status table used by the PNSD; 
         FIG. 5  is a high level flow of the PNSD software used to manage the preemption requests; 
         FIG. 6  is a flow that illustrates the concept of  FIG. 4  applied to the system of  FIG. 2 ; 
         FIG. 7  is a more detailed flow diagram of  FIG. 5  for the PNSD software used to manage the preemption requests; and 
         FIG. 8  is a more detailed flow diagram of  FIG. 5  for the PNSD software used to manage the resume requests. 
     
    
    
     DETAILED DESCRIPTION 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention. 
     The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically. The terms program, software application, and the like as used herein, are defined as a sequence of instructions designed for execution on a computer system. A program, computer program, or software application may include a subroutine, a function, a procedure, an object method, an object implementation, an executable application, an applet, a servlet, a source code, an object code, a shared library/dynamic load library and/or other sequence of instructions designed for execution on a computer system. 
     Multiple Processor System in Parallel Computing System 
       FIG. 1  is a block diagram showing an example multiple processor system  100  in a parallel computing system. As shown in  FIG. 1 , system  100  includes a plurality of processors  110  at each of a plurality of respective nodes or computing nodes  120 . Each processor  110  can be referred to as a “host system”. Each processor is implemented as a single processor having a single CPU or as a multiple processor system having a plurality of CPUs which cooperate together on processing tasks. An example of a processor  110  is a server such as a “Symmetric Multiprocessor” (SMP) system sold by the assignee of this application. Illustratively, a server such as an SMP may have from a few CPUs to 32 or more CPUs. Each processor, e.g., each server, includes a local memory  115 . Each processor  110  operates semi-autonomously, performing work on tasks as required by user applications and one or more operating systems that run on each processor, as will be described further with respect to  FIG. 2 . Each processor is further connected via a bus  112  to a communications adapter  125  (hereinafter “adapter”) at each node  120 . The adapter, in turn, communicates with other processors over a network, the network shown here as including a switch  130 , although the network could have a different topology such as bus, ring, tree, etc. Depending on the number of CPUs included in the processor  110 , e.g., whether the processor is a single CPU system, has a few CPUs or is an SMP having many CPUs, the adapter can either be a stand-alone adapter or be implemented as a group of adapter units. For example, when the processor  110  is an SMP having 32 CPUs, eight adapter units, collectively represented as “adapter”  125 , service the 32 CPUs and are connected to the 32 CPUs via eight input output (I/O) buses, which are collectively represented as “bus”  112 . Each processor is connected to other processors within system  100  over the switch  130 , and to storage devices  140 . Processors  110  are also connected by switch  130  to an external network  150 , which in turn, is connected to one or more external processors (not shown). 
     Storage devices  140  are used for paging in and out memory as needed to support programs executed at each processor  110 , especially application programs (hereinafter “applications” or “user space applications”) at each processor  110 . By contrast, local memory  115  is available to hold data which applications are actively using at each processor  110 . When such data is no longer needed, it is typically paged out to the storage devices  140  under control of an operating system function such as “virtual memory manager” (VMM). When an application needs the data again, it is paged in from the storage devices  140 . The scheduler/load leveler  160  provides job scheduling and an advance reservation system for the parallel computing system  100 . 
     To efficiently utilize the resources of the computing environment, scheduling techniques are used to schedule execution of computer jobs of the environment. As noted above, resource bookkeeping is traditionally buried in the lowest levels of the job scheduling logic, making it difficult and time consuming to extend existing job scheduling algorithms with new paradigms, such as backfill and preemption. (Again, this resource bookkeeping is the tracking of used, free, bad, and to-be-used resources in the job scheduling algorithm.) In view of this, presented herein is a clear and well-defined decoupling of the job scheduling algorithm from responsibility for maintaining the job&#39;s recorded resource usages. 
     Communication Protocol Stack 
       FIG. 2  illustrates an example communication protocol stack operating on a processor  110  in a parallel computing system  100  such as that shown in  FIG. 1 . As shown in  FIG. 2 , the resources of the processor, including its memory, CPU instruction executing resources, and other resources, are divided into logical partitions known as LPARs (LPAR 1 , LPAR 2 , . . . , LPAR N). In each logical partition, a different operating system (OS-DD  202 ) may be used, such that to the user of the logical partition it may appear that the user has actual control over the processor. In each logical partition, the operating system  202   a ,  202   b , and  202   c  controls access to privileged resources. Such resources include translation tables that include translation information for converting addresses such as virtual addresses, used by a user space application running on top of the operating system, into physical addresses for use in accessing the data. 
     However, there are certain resources that even the operating system is not given control over. These resources are considered “super-privileged”, and are managed by a Hypervisor layer  250  which operates below each of the operating systems. The Hypervisor  250  controls the particular resources of the hardware  260  allocated to each logical partition according to control algorithms, such resources including particular tables and areas of memory that the Hypervisor  250  grants access to use by the operating system for the particular logical partition. The computing system hardware  260  includes the CPU, its memory  115  and the adapter  125 . The hardware typically reserves some of its resources for its own purposes and allows the Hypervisor to use or allocate the rest of its resources, as for example, to each logical partition. A network resource table as described in  FIG. 3  defines all of the network resources assigned to each parallel job executing on each LPAR. 
     Within each logical partition, the user is free to select the user space applications and protocols that are compatible with the particular operating system in that logical partition. Typically, end user applications operate above other user space applications used for communication and handling of data. For example, in LPAR 2 , the operating system  202   b  is AIX, and the communication protocol layers HAL  204 , LAPI  206  and MPI  208  operate thereon in the user space of the logical partition. One or more user space parallel applications operate above the MPI layer  208 . In this example the operating system  202   a  is LINUX in LPAR  1 . Other logical partitions may use other operating systems and/or other communication protocol stacks. In one embodiment, running on each LPAR is a PNSD (Protocol Network Services Daemon). Each LPAR maintains its own status table as shown in  FIG. 4  to manage preemption requests by the PNSD Each PNSD application manages preemption requests for parallel jobs on each LPAR with status tables as shown in  FIG. 4 . The status table shown in  FIG. 4  is associated with each parallel job. This PNSD application is further described in reference to flow diagrams in  FIGS. 5 and 6  below. Also on each LPAR, a Scheduler Agent  212  communicates with the Scheduler  160  of  FIG. 1  to schedule various parallel user space applications  214  that have multiple tasks distributed across the parallel computing system of  FIG. 2 . 
     Network Resource Table 
       FIG. 3  illustrates an example is Network Resource Table. Shown are three tables for three jobkeys  302 ,  322 , and  342 . Each key or jobkey has associated with it the taskIDs,  304 ,  324 , and  344 , for the user space parallel application or job. The computing node  306 ,  326 , and  346  and the adapter  308 ,  328  and  348  are also associated for each task as shown. The use of the key  302 ,  322 , and  342  provides a quick index into the network resource table for retrieving the address locations of each task, node and adapter for a parallel application. Although these network resource tables as shown as three separate tables in this illustration, other table configurations are possible within the true scope and spirit of the present invention. 
     Task Status Table 
       FIG. 4  illustrates an example is Status Table for each task associated with a parallel application. A status job is associated with each parallel application or parallel job running on each LPAR. It should be understood that this status table allows for managing the preemption requests by the PNSD application as further described below. 
     Shown are example states for tasks that are responded to a preemption request i.e. task  1   402  preempted, task  2   404  preempt_failed, task  3   406  preempted, task  4   408  preempted, and  410  task  5  preempt_in_progress. 
     Also shown in  FIG. 4  are example states for tasks that are responded to a resume in preemption request i.e. task  1   442  preempted, task  2   444  resumed, task  3   446  resumed, task  4   448  resumed_in_progress, and  450  task  5  resumed_in_progress. It should be noted that these are example states and other states are possible such as not-responding if a task hangs. The settings of these preemption states in the status table is further described in  FIGS. 5 ,  6 , and  7  below. 
     High Level Flow 
       FIG. 5  illustrates a high level flow of the PNSD software used to manage the preemption requests. The process begins in step  502  and immediately proceeds to step  504  where a request is received from a scheduler/load leveler  160  by the PNSD application. The PNSD access the network resource table of  FIG. 3 . A loop begins in step  510 , by setting a loop count equal to the number of tasks associated with the key for the job or parallel application in  FIG. 3 . The process continues in step  512  by sending a request to each task, node, and adapter resource using the information listed in the network resource table for the job key. Any replied received from a task is written into a status table of  FIG. 4  in step  514 . The counter decrements in step  516  and the process continues to repeat steps  510  through  516  until a request and response, if any (because the task could be hung and a timeout routine used to recover the task) is written into the status table. At the completion of this loop, the status for each task associated with the parallel application is gathered and records in the status table of  FIG. 3 . The over all status is then sent to the scheduler in step  518  and the process ends in step  520  until the next request is received. It is important to note that this flow reduces the complexity of the scheduler having to communicate with each task individually. The PNSD application manages preemption at each OS instead of job scheduler managing preemption per process/task as performed in the prior the art. 
     Applying High Level Flow to System 
       FIG. 6  is a flow that illustrates the concept of  FIG. 4  applied to the system of  FIG. 2 . The scheduler/load leveler  160  of  FIG. 1  broadcasts a preemption requests to parallel computing system and each PNSD application  210 , shown as  210   a  and  210   b  here to denote to different PNSD on two different logical partitions, such as those shown in  FIG. 2 , receives the request. Using the network resource table in  FIG. 3  to get the information associated with the key for the parallel job or parallel application. A request is send by the PNSD application  210   a  and  210   b  to each of the tasks associated with the parallel job. As shown PNSD  210   a  sends a request to tasks  602 ,  604 ,  606 , and  608 . A reply is recorded in the status table of  FIG. 4 . Likewise PNSD  210   b  sends a request to tasks  652 ,  654 ,  656 , and  658  and again a reply is recorded in the status table of  FIG. 4 . This provides preemption thread release/reacquire of each network resource as shown in  603  and  653 . 
     Detailed Level Flow of Managing Preemption Request 
       FIG. 7  is a more detailed flow diagram of  FIG. 5  for the PNSD software used to manage the preemption requests. The process begins with a preempt request command received from the scheduler/load leveler  160  of  FIG. 1 . A first test is made to ensure a valid jobkey is present in the request in step  702 . If an invalid job key, an error is reported in steps  716  and  720 . In the case when the job key is valid, a check is made to determine if a resource such as an adapter resource is reserved in step  704 . Before a parallel job can run, the resources allocated for the job must be reserved for the job. Preemption allows one job to grab the resources from another job. In the case where the resource is not reserved, the process continues to step  718  where the status table in  FIG. 4  is updated with preemption state set to “preempted” the process send by sending a reply to the requester in step  720 . If the resource is reserved, a test to is made by review the status table of  FIG. 4  to see if all the tasks associated with the parallel job or parallel application are ready. If the process/tasks are not ready in step  706 , then an error is reported in steps  716  and  720 . In the case where process/tasks are ready in step  706  the preemption status in the status table of  FIG. 4  is set to “preempt_in_progress” in step  708  and the preemption bits marked in steps  710 . The request to preempt the process or thread sent in step  714  is created and sent in step  720 . 
     For the preempt reply flow, the preemption status in status table in  FIG. 4  is cleared in step  730 . A test is made to determine if there is an error in the reply  732  and in the event there is an error in the reply the status table is set to “preempt_failed”. The process loops in step  736  until all replies are received. In the case there was a failure, the process returned an error code in step  744  and  746 . In the case where the preempt_failed is false in step  738 , the network resources or windows for resume reply are unreserved in step  742  and the status table in  FIG. 4  is updated with preemption state set to “preempted” in step  740  and the process send by sending a reply to the requester in step  746 . As stated above it is important to note that before a parallel job can run, the resources allocated for the job must be reserved for the job. Preemption allows one job to grab the resources from another job. So after preemption, the job being preempted must release resources. That&#39;s done after premption replies are received. Prior to resume, it is important to ensure the job resources are not reserved/used by other jobs and reserve the resources before asking the tasks to resume. 
     Detailed Level Flow of Managing Resume Request 
       FIG. 8  is a more detailed flow diagram of  FIG. 5  for the PNSD software used to manage the resume requests. The process begins with a preempt request command received from the scheduler/load leveler  160  of  FIG. 1 . A first test is made to ensure a valid jobkey is present in the request in step  802 . If an invalid job key, an error is reported in steps  816  and  826 . In the case when the job key is valid, a check is made to determine if a resource such as an adapter resource is reserved in step  804 . In the case where the resource is reserved, the process continues to step  820  where the status table in  FIG. 4  is updated with preemption state set to “resumed” the process send by sending a reply to the requester. If the resource is not reserved, a test to is made by review the status table of  FIG. 4  to see if all the tasks associated with the parallel job or parallel application are ready. If the process/tasks are not ready in step  806 , then an error is reported in steps  816  and  826 . In the case where process/tasks are ready in step  806 , the all a test is made to see if the process/task is preempted or preempt_failed in step  808 . If the tasks/process are not preempted or preempt_failed, an error is set in step  816  and sent back to schedule in step  826 . In the case the preempted or preempted_failed is set, then preemption status in the status table of  FIG. 4  is set to “resume_in_progress”. Next, in step  812  the parallel application or job resources are reserved. The preemption event bits are sent in step  814  and the request to preempt the process or thread sent in step  818  is created and sent in step  826 . 
     For the resume reply flow, the preemption status in status table in  FIG. 4  is cleared in step  830 . A test is made to determine if there is an error in the reply  832  and in the event there is an error in the reply the status table is set to “resume_failed”. The process loops in step  836  until all replies are received. In the case there was a failure, the process returned an error code in step  842  and  844 . In the case where the resume_failed is false in step  738 , the status table in  FIG. 4  is updated with preemption state set to “resumed” in step  840  and the process send by sending a reply to the requester in step  844 . 
     NON-LIMITING EXAMPLES 
     The present invention as would be known to one of ordinary skill in the art could be produced in hardware or software, or in a combination of hardware and software. However in one embodiment the invention is implemented in software. The system, or method, according to the inventive principles as disclosed in connection with the preferred embodiment, may be produced in a single computer system having separate elements or means for performing the individual functions or steps described or claimed or one or more elements or means combining the performance of any of the functions or steps disclosed or claimed, or may be arranged in a distributed computer system, interconnected by any suitable means as would be known by one of ordinary skill in the art. 
     According to the inventive principles as disclosed in connection with the preferred embodiment, the invention and the inventive principles are not limited to any particular kind of computer system but may be used with any general purpose computer, as would be known to one of ordinary skill in the art, arranged to perform the functions described and the method steps described. The operations of such a computer, as described above, may be according to a computer program contained on a medium for use in the operation or control of the computer, as would be known to one of ordinary skill in the art. The computer medium, which may be used to hold or contain the computer program product, may be a fixture of the computer such as an embedded memory or may be on a transportable medium such as a disk, as would be known to one of ordinary skill in the art. 
     The invention is not limited to any particular computer program or logic or language, or instruction but may be practiced with any such suitable program, logic or language, or instructions as would be known to one of ordinary skill in the art. Without limiting the principles of the disclosed invention any such computing system can include, inter alia, at least a computer readable medium allowing a computer to read data, instructions, messages or message packets, and other computer readable information from the computer readable medium. The computer readable medium may include non-volatile memory, such as ROM, Flash memory, floppy disk, Disk drive memory, CD-ROM, and other permanent storage. Additionally, a computer readable medium may include, for example, volatile storage such as RAM, buffers, cache memory, and network circuits. 
     Furthermore, the computer readable medium may include computer readable information in a transitory state medium such as a network link and/or a network interface, including a wired network or a wireless network that allows a computer to read such computer readable information. 
     Although specific embodiments of the invention have been disclosed, those having ordinary skill in the art will understand that changes can be made to the specific embodiments without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted, therefore, to the specific embodiments, and it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention.