Abstract:
An improved method and apparatus for time stamping events occurring on a large scale distributed network uses a local counter associated with each processor of the distributed network. Each counter resets at the same time globally so that all events are recorded with respect to a particular time. The counter is stopped when a critical event is detected. The events are masked or filtered in an online or offline fashion to eliminate non-critical events from triggering a collection by the system monitor or service/host processor. The masking can be done dynamically through the use of an event history logger. The central system may poll the remote processor periodically to receive the accurate counter value from the local counter and device control register. Remedial action can be taken when conditional probability calculations performed on the historical information indicate that a critical event is about to occur.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not Applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED-RESEARCH OR DEVELOPMENT  
       [0002]     This invention was developed under Subcontract No. B517552 between the Regents of the University of California Lawrence Livermore National Laboratory and IBM T.J. Watson Research Center.  
       INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC  
       [0003]     Not Applicable.  
       FIELD OF THE INVENTION  
       [0004]     The invention disclosed broadly relates to the field of computer network management. More particularly, the present invention relates to hardware and software for monitoring and capturing the behavior of undesired events and event generating components or subsystems on a distributed system through indirect time stamping and performance of online and offline dynamic masking of the event information for probing and minimization of future undesirable events.  
       BACKGROUND OF THE INVENTION  
       [0005]     A distributed system typically contains a plurality of processors, subsystem components, instruments and other electronic devices. These may include a number of software and real-time system monitoring devices for system environmental parameters. These devices, processors, intra processor components, system software and hardware components need to be synchronized with one another in order to correlate the occurrence of any usual or unusual software or hardware events spanning over one or more independent functional units. Thus, the synchronization in time to a desired precision level affects both the design and the debugging of the distributed system before and after the hardware manufacture.  
         [0006]     With respect to the occurrence of faults in large scale distributed systems, logging hardware and software events, isolating faults and identifying problems are some of the most difficult tasks to perform. In order to achieve these features, it is necessary to precisely order the events in terms of their occurrence through synchronized time stamps. Usually time stamps are obtained by issuing system calls to the operating system. However, this approach does not address problems such as, once a node fails, there is no guarantee that the system call will be able to obtain the time stamp successfully executed. In addition, there is a non-deterministic processing time to service the system call which makes precise time stamping difficult. Furthermore, multiple error events may get the same time stamp which prevents event ordering. Even if an ordering scheme through indirect time stamping can solve such a problem, it is time consuming to record the events, process these events and then take action for the system. Finally, if all events get the same treatment in terms of preprocessing and taking an action, the time required to take an action might be too long to prevent short term events accruing within a particular node. Hence there is a need, not only to precisely record the occurrences of faults without system intervention, but also to design a system which is able to address the long term and short term events in such a manner that the action plan is more effective. There is also a requirement to have the machine state of any distributed system properly frozen for future debugging and probing.  
       SUMMARY OF THE INVENTION  
       [0007]     An embodiment of the present invention is directed toward a distributed network having a plurality of processors. A local counter is associated with each of a plurality of processors in the distributed network. An event register is associated with each of the local counters. A system monitor receives a counter value from the local counter in response to an event being registered in the event register. The system monitor includes an event logger for storing information concerning at least a portion of the events. The event logger preferably records data concerning a type of event registered by the event register and a time an event occurred. The event register remains frozen until the event register is read by a monitoring system. Masking mechanisms filter the event register outputs to differentiate between critical and non-critical events. The masking is dynamically updated during online processing. During offline analysis conditional probability calculations are done to prepare the conditional probability table. During online analysis conditional probability lookups are performed to determine if a probability of an event occurring has exceeded a threshold level and to determine if remedial or accommodative action needs to be taken. The counter is preferably 64 bits or more in width to insure an accurate time stamp. The event register preferably includes an error time stamp register that receives a value from the local counter when an event occurs and an error occurred register that indicates to the system monitor that an error event has occurred.  
         [0008]     Another embodiment of the present invention is directed toward a method of producing a time stamp for an event occurring on a distributed network that includes a plurality of processors. According to the method, a local counter value is produced for each of a plurality of processors in the distributed network with an associated counter. The local counter at each of the processors is synchronized with a global clock. The local counter for a processor is frozen when an event associated with the processor occurs. The local counters are periodically polled with the system monitor. The events are dynamically filtered based on a recorded history of information associated with the occurrence of events such that only critical events are reported to the system monitor. During online analysis, conditional probability lookups are performed to determine if a probability that a critical event will occur exceeds a threshold level and preventative action is performed if such threshold is exceeded. Events that occur are dynamically masked based on conditional probabilistic lookups using machine learning algorithms during online analysis. The type of event that occurred is determined and whether or not to produce a global alert, synch stop or machine check alert signal is determined based upon the type of event that occurred. Offline analysis is used to update the history table and conditional probabilities and determine when online analysis of a problem is possible.  
         [0009]     Yet another embodiment of the present invention is directed toward a distributed computer system having hardware and software for implementing a time stamping process to produce a time stamp associated with an occurrence of an error event. The distributed computer system includes a plurality of local counters wherein each counter is associated with a particular processor or system in the distributed computer system. An event register records event information concerning an occurrence of a critical event associated with the processor and event register. An event logger receives and logs information concerning the occurrence of the events. A global clock synchronizes the local counters. Dynamic masks or filters are created based upon historical event information to determine whether or not an event that occurred is a critical event. Software evaluates events based on conditional probabilistic calculations and schedules remedial or preventative action accordingly during online analysis.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a block diagram of an event logging mechanism according to an embodiment of the present invention;  
         [0011]      FIG. 2  is a top level flow chart for determining whether to use online analysis or offline analysis according to an embodiment of the present invention;  
         [0012]      FIG. 3  is a flow chart of a preferred offline mechanism for implementing an embodiment of the present invention;  
         [0013]      FIG. 4  is a first portion of a flow chart of a preferred online mechanism for implementing an embodiment of the present invention;  
         [0014]      FIG. 5  is a second portion of a flow chart of a preferred online mechanism for implementing an embodiment of the present invention;  
         [0015]      FIG. 6  is diagram of a preferred dynamic grouping mechanism according to an embodiment of the present invention;  
         [0016]      FIG. 7  is history table structured in accordance with an embodiment of the present invention;  
         [0017]      FIG. 8  is a diagram of a hardware implementation of an embodiment of the present invention; and  
         [0018]      FIG. 9  is a block diagram of an information handling system that can be used to implement an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     The present invention provides hardware and software mechanisms that achieve accurate time stamping through indirect means and dynamic masking mechanisms for online event isolation and control. Both the hardware and software dynamic masking mechanisms are based on conditional probabilistic calculations using machine learning algorithms. The conditional probabilities and event histories are updated during offline analysis. Event prediction and process migration is performed during online analysis.  
         [0020]     Referring to  FIG. 1 , an illustration of a software and hardware based indirect time stamping and event logging mechanism  100  for a distributed system of processors  102  constructed in accordance with an embodiment of the present invention is shown. In a preferred embodiment, each processor  102  in the distributed system has a hardware register with a counter  103 . The counters  103  are most preferably more than 64 bits in width such that they provide a high level of accuracy. The counters  103  are synchronized through links  121  with a global clock/counter synchronizer  104  that resets the counters  103 . The hardware counters  103  are used to log error events that occur with their associated processor  102 . An error occurred value in the registers  103  is initially set to FALSE. Once an error has been detected, a time stamp for the error is recorded in the registers  103  and the error occurred value is set to TRUE. Once the register  103  value has been read by the event logger  105  through links  122 , the error occurred value is reset to FALSE. The registers and counters  103  are also reset once the information has been polled out of the registers and counters  103  for entry into the event logger  105 . Online interrupts can be triggered globally based on the events collected through the use of a global interrupt as discussed in more detail below.  
         [0021]     The use of a dedicated register and counter  103  allows a more accurate time stamp to be obtained without a system call by the clock  104  to obtain the time stamp for an event that occurred. In accordance with the approach, the clock  104  is synchronized to a higher accuracy than the accuracy level at which the error events are collected. Thus, the clock&#39;s  104  accuracy level may be on the order of 1 microsecond throughout while the distributed system records the time in increments of seconds. To collect the events at a higher level of accuracy, the counters  103  are selected to be large enough to provide a high degree of resolution within the required recording accuracy time. Each counter  103  resets at the same time globally within the distributed system. Thus, all events, irrespective of the processor  102  at which they occur, can be time stamped at a particular instant and counter  103  value which is frozen when the event occurs at the particular processor  102  or chip. In addition, event information  108  is passed from the memory  106  to the registers  103  when an error event occurs. The registers  103  preferably include a device control register that stores event type information related to the occurrence of an event. Since the counter  103  value is frozen in the register  103 , the accuracy of the system event recording can be independent of the frequency at which the events are polled from the processors  102  or chips to be recorded globally through the event logger  105 . Although a global synchronized clock time is preferred, the approach can easily be extended to cluster systems that do not have such a clock  104 .  
         [0022]     The global event logger  105  registers the counter  103  based event logs in an order that is based on the counter values from the counters  103 . The event logger  105  can be implemented using a history table which preferably contains an event identification number, event type and counter value in a standard text format. The event logger  105  obtains logging information such as that set forth above from the register counters  103  through links  122 . The global clock  104  is used to synchronize the counters  103  through links  121 . Thus, the global clock  104  time is related to the local counters&#39;  103  counts. Event information  108  is passed from the hardware memory  106  to the registers  103 . An example of such an event would be an interrupt due to a malfunction. The registers  103  can then be polled by a system monitor for event information according to a time-based schedule or in response to interrupt signals.  
         [0023]     Referring now to  FIG. 2 , a top level flow chart describing a method for analyzing an error event with offline and online analysis according to an embodiment of the present invention is shown. Generally, offline analysis will be a continuous process which is carried out independently of the online analysis processes. The method starts in step  201  with a check to see if an error event has occurred. If no error event has occurred, the method returns to step  201  to wait for the occurrence of an error event. If an error event has occurred, the method proceeds to step  202  wherein the error event is reported for offline analysis. Once offline analysis has been completed, the method determines in step  205  if online analysis is possible. Online analysis is only possible when dynamic event groups are well established and conditional probability calculations are complete offline. If dynamic masks and masking events can not be established through an available list of error events downloaded from a history table, the online masking process waits until sufficient information is available from the offline processes. If online analysis is possible, the error event is handled through online analysis in step  203 . If online analysis is not possible in step  205 , the method returns to the loop of step  201  wherein it waits for the next error event to occur. As discussed in more detail below, the use of online analysis reduces the time required to migrate a process away from the likely occurrence of a critical event.  
         [0024]     Referring now to  FIG. 3 , a preferred offline mechanism for implementing an embodiment of the present invention is shown. The mechanism first determines if events for offline analysis have been received in step  300 . If events for offline analysis have not been received, the mechanism loops back to step  300  until an event for offline analysis is received. If an event for offline analysis has been received, the mechanism proceeds to update the history table in step  301 . The mechanism also updates the conditional probabilities for events associated with the event in step  302 . Conditional probability calculations are performed to determine the probability of the associated critical event occurring. The probability of an event occurring is preferably based upon a time window size that is selected by the designer that determines which events are considered associated. In step  303 , the mechanism determines if a conditional probability has been established for all critical events. If a conditional probability has not been established for all events, the mechanism returns to step  300  wherein it waits for an event for offline analysis. If a conditional probability has been established, the mechanism sets on online analysis register value to one in step  304  and waits for the next offline analysis event to be received.  
         [0025]     Referring now to  FIG. 4 , an online mechanism for handling the occurrence of error events during online processing is shown. The online mechanism first loads the recent history and conditional probability tables in step  401 . The online mechanism then determines if an online analysis event has been received in step  402 . If not, the mechanism loops back to step  402  until an online analysis event is received. If an online analysis event has been received, the mechanism uses the history table and the conditional probability table to try to spot future critical events in step  403 . The set of events can be checked to determine which events are the most critical and what further events are associated with their occurrence. In step  404 , the mechanism determines if the probability of the occurrence of a critical event has surpassed a lower threshold level. If such a critical event is not predicted, the mechanism returns to step  402  wherein it waits to receive an online analysis event. If such a critical event is predicted, the mechanism updates its dynamic masking and sets a time-out period in step  405 . The dynamic masking reduces the processing time during online analysis, so that short term actions can be taken.  
         [0026]     The mechanism then proceeds to step  408  as shown in the flow chart of  FIG. 5 . The mechanism of  FIG. 5  waits to receive an online analysis event in step  501 . When an online analysis event is received, the mechanism determines if the time-out period has elapsed in step  502 . If the time-out period has not elapsed, the online mechanism determines if the probability of the occurrence of a critical event has converged toward a higher threshold value in step  503 . If a critical event is predicted to occur, the online mechanism takes action in step  510  to migrate the process away from the predicted critical event occurrence, schedule maintenance, etc. The online mechanism evaluates the probability that the associated events will occur in determining what type of remedial action needs to be taken. Once the remedial action is taken, the mask is reset in step  521  and the mechanism returns to step  406  of  FIG. 4  wherein the online analysis mechanism restarts. If the time-out period has elapsed in step  502 , the mask is reset in step  521  to zero and the online mechanism is restarts in step  406 .  
         [0027]     Referring now to  FIG. 6 , a simplified dynamic grouping mechanism in accordance with an embodiment of the present invention is shown. Consider that a series of events are being recorded from a system in a table  603 . The table  603  contains processed information from an event logger. Consider that a set of five events ( 604 ) are found to occur associating a critical event  3  ( 620 ). Based on table  603 , conditional probability values for each event or set of events associated with critical event(s)  620  are recorded into probability history table ( 700 ) in  FIG. 7  during offline analysis. So, when a series of events ( 605 ) occur in a system, at any instant of time, we lookup the conditional probabilities of the events and figure out whether the joint probability associated with the events so far has reached a lower threshold value. A dynamic grouping mechanism ( 606 ) of the events happening on a system with our target event(s) (the critical event(s) three ( 620 )) help to choose the probabilities and joint probabilities from the probability table ( FIG. 7 ). If the joint probability ( 705 ) or conditional probability ( 704 ) reaches a specified lower threshold value then the online mechanism is ready to take action through  510  in  FIG. 5 . A preferred embodiment of the present invention uses online conditional probability based filtering mechanisms. The conditional probability information is contained in a probability history table ( FIG. 7 ). The probability history table also contains information related to the severity of the events and the non-critical events that are associated with the critical events. Referring now to  FIG. 7 , a preferred history table  700  with conditional probability information in accordance with an embodiment of the present invention is shown. The history table  700  contains a list of critical events  701  that may occur on a distributed network. For each critical event  701 , event type information  702  that indicates the severity of the occurrence of the event  701  is stored. A list of associated non-critical events  703  contains the non-critical events that are associated with the occurrence of the critical event  701 . The history table  700  also contains the conditional probabilities  704  and joint probabilities  705  for each of the associated non-critical events. The joint probability is a probability that a sequence of ( two or more) non-critical events happens before a critical event. The conditional probability and joint probability are calculated for insertion into the probability history table during offline analysis.  
         [0028]     Based on offline and online analysis, global masks can be designed. The dynamic masking process identifies a particular set of critical events and the associated cloud of non-critical events occurring in the neighborhood of the critical event. Dynamic groups are then established based on the type of critical events and the associated non-critical events. The number of non-critical events to be included within the grouping mechanism is determined by the designer, type of system and the number of simultaneous events that are required to be listed as critical events.  
         [0029]     Referring now to  FIG. 8 , a preferred hardware implementation of the dynamic masking process of an embodiment of the invention is shown. Dynamic groups  801  are established based upon the type of critical event and the associated non-critical events. Based on offline and online analysis, global masks  808  are designed AND gates  812  are used to mask and unmask events. An OR gate  803  is also used to record the final time stamp and event type in the event logger. The events are masked or filtered such that information is only collected for critical events and associated non-critical events. A variety of techniques can be used to mask the events. For example, a device control register mask may be used to filter information from the counters and registers such that only certain critical events result in a global alert, machine check alert or synchronization stop signal being generated by the system monitor or service/host processor. The collected information for a critical event preferably includes a counter value  804 , time stamp  805  calculated based on the synchronized clock and event type  806 . The counter value  804  is reset  807  after the error information is read. A global interrupt  810  is used to trigger online interrupts globally based upon the occurrence of the event. Global dynamic mask generators  811  may be customized to filter specific events through any type of desired bit masking mechanism.  
         [0030]     Referring now to  FIG. 9 , a block diagram of an information handling system  900  that can be used to implement an embodiment of the present invention is shown. The system  900  includes a processor  906 , a random access memory  902 , read only memory  904  and input/output interface  910 . Additionally, a disk drive subsystem  912 , input/output controller  908  a mass storage device  918  and interface  914 , and a CD ROM drive  916  are included. The processor  906  has a system-on-chip embodiment of the counters, registers and masks as discussed herein. When an error event occurs on the system  900 , a local time stamp is recorded for the error event. Event information including the time stamp is sent from the system  900  through the input/output interface  910  to a remote monitoring system that logs the information and decides upon remedial or preventive action. Software can be loaded on a computer readable medium, such as the diskette  903  or CD ROM  901 , to operate the programmable computer system  900  according to an embodiment of the present invention.  
         [0031]     What has been shown and discussed is a highly-simplified depiction of a programmable computer apparatus. Those skilled in the art will appreciate that other low-level components and connections are required in any practical application of a computer apparatus. Therefore, while there has been described what is presently considered to be the preferred embodiment, it will be understood by those skilled in the art that other modifications can be made within the spirit of the invention.