Abstract:
Method and system for repairing memory failure in a computer system in one aspect determines one or more test patterns and time duration for testing the new memory unit that replaced a failed memory unit. The test pattern is written to the new memory unit and read from the new memory unit. The read pattern is compared to the test pattern that was used to write. If the read test pattern and the written test pattern doe not match, a further repair action is taken. If they match, writing and reading of the test pattern repeats until the time duration for testing expires. The new memory unit may be configured as available for use when the write and read test completes successfully for the testing time duration.

Description:
FIELD OF THE INVENTION 
   The present invention generally relates to computer memories and particularly to detecting and repairing memory failures. 
   BACKGROUND OF THE INVENTION 
   In high availability nonstop production environments concurrent recovery, repair and extensive testing of replacement memory such as DIMMS (dual in-line memory module) memory is highly desirable. Replacement memory DIMMs are prone to early life failures, contamination during shipment or installation. Improper installation processes often cause replacement DIMMs to fail. Replacement DIMMs frequently fail shortly after the memory is returned to the production use and under stress. 
   Conventional testing of replaced memory DIMMS typically involve background read only memory scrubbing techniques to clean up single bit errors and detect multiple bit errors in the system installation environment. Also in conventional testing methodologies that perform a write test, the entire productive system is disabled to accommodate the write test. These two methods and others like it either require a different system installation environment than the production environment or disruption of the production services or applications. 
   Accordingly, it is desirable to have a system and method that would allow a production system to have memory concurrently installed and stressed and verified in the actual production environment without affecting the production environment. This would allow the customer and the IT supplier to more confidently return repaired components after failure to production and verify replacement component. 
   SUMMARY OF THE INVENTION 
   A method and system for repairing memory failure in a computer system are provided. The method in one aspect comprises receiving a command that a failed memory unit has been replaced and to test the new memory unit in a memory subsystem having one or more memory units concurrently being used by a running processor, determining a test pattern, and determining a time duration for testing the new memory unit. The method further includes writing the test pattern to the new memory unit, reading the written test pattern from the new memory unit, and comparing the test pattern read with the test pattern that was written. If the read test pattern and the written test pattern do not match, the method may further include notifying that the new memory unit is bad and if the read test pattern and the written test pattern match, determining if the time duration for testing has expired. If the time duration has not expired, the method further may include repeating the steps of writing, reading, and comparing. If the time duration has expired, the method may further include configuring the new memory as being available for use. 
   A program storage device readable by machine, tangibly embodying a program of instructions executable by the machine to perform the above method steps for repairing memory failure in a computer system is also provided. 
   A system for recovering memory failure in a computer system, in one aspect may comprise a processor operable to receive a command that a failed memory unit has been replaced and to test the new memory unit in a memory subsystem of a computer system. The memory subsystem may have one or more memory units. The processor may be further operable to determine a test pattern and determine time duration for testing the new memory unit. The processor further may be operable to write the test pattern to the new memory unit, read the written test pattern from the new memory unit, and compare the test pattern read with the test pattern that was written. If the read test pattern and the written test pattern do not match, the processor may be operable to notify that the new memory unit is bad and if the read test pattern and the written test pattern match, the processor may be operable to further determine if the time duration for testing has expired. If the time duration has not expired, the processor may be operable to repeat the steps of writing, reading, and comparing, and if the time duration has expired, the processor may be operable to configure the new memory as being available for use. 
   Further features as well as the structure and operation of various embodiments are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a computer with a single copy of real memory and multiple memory DIMMS. 
       FIG. 2  illustrates a method flow of general events according to the present invention in one embodiment. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  is a block diagram illustrating computer components and a single copy of real memory and multiple memory DIMMs. While the description in the present disclosure refers to DIMMs as examples of memory units, it should be understood that the system and method of the present disclosure applies to any other memory unit, known or will be known, and therefore, is not limited to DIMMs only. In one embodiment of the present invention, a part of a repair action, for instance, at the customer&#39;s or service technician&#39;s direction, performs write and read tests on memory DIMMS or a single DIMM before returning the replaced memory DIMM or DIMMs to operating system use. In  FIG. 1 , a computer system has a central processing unit (CPU)  102 , Service Processor  101 , Memory Bus  103 , Service Processor writing net  100 , Memory Controller  104 , Memory Chip  107  on Memory DIMM  106 . Memory DIMM  105  is another DIMM like the Memory DIMM  106 . The I/O (input/output) portion of the computer has been omitted for clarity but is not excluded from the scope of the invention as existing in a typical computer. The CPU may run operating system such as AIX5L. A service processor  101  may also have its own operating system such as a Linux derivative. A service processor  101  has the ability to send commands, data and execute programs at a microcode level to all components of a computer. Each component may be wired to the service processor  101  on its own bus network. In other embodiments, a BIOS ROM and or RAM or the like may be used instead of a service processor. The functions disclosed in the present disclosure may be implemented in a service processor or BIOS or the like. A memory bus  103  usually exists between a CPU  102  or CPUs that connect to a memory controller  104  that in turn can individually communicate with each addressable area of the memory subsystem  110 . In one embodiment, each memory chip on a DIMM contains storage and logic to perform memory operations and send and receive commands and data from the memory controller. 
     FIG. 2  is flow diagram illustrating method steps of the present invention in one embodiment. At step  200 , a computer is running. The computer, for instance, may be a general purpose computer such as an IBM P-Series POWER5 server running AIX 5L operating system. The computer may be performing normal application processing and operating system functions such as I/O, virtual memory demand paging, network input and output to other computers or networks, etc. 
   In one embodiment, the memory subsystem has the ability to detect errors that are both recoverable and unrecoverable. Recoverable errors can be corrected with Error Correcting Codes, ECC. A counter in an implementation dependent location in the memory subsystem is kept of the number of recoverable errors in a particular memory chip. A threshold is met after and appropriate number of recoverable errors to force the proactive removal of the memory chip such as the Memory DIMM shown at  107  ( FIG. 1 ). At step  202 , a memory recovery event occurs when the threshold is reached or exceeded. 
   At step  204 , the logic in DIMM ( FIG. 1   106 ) creates an interrupt to the operating system via the memory controller  104  to relocate the contents of memory from memory chip ( FIG. 1   107 ) to another DIMM such as the one shown at  105  in  FIG. 1 . This may cause the contents of a memory chip in DIMM  105  to be paged out to paging storage if, for example, real memory demands are such that there is not enough free real memory. 
   A service processor ( FIG. 1   101 ) also receives this event and sends commands to the memory controller ( FIG. 1   104 ) to create interrupts to the operating system to relocate the remaining contents of memory for the remaining memory chips on DIMM  106 . In this example, the remaining contents may be stored to DIMM  105  or be paged out to paging storage. In another embodiment, with virtualized server partitions a hypervisor layer may be called to perform memory configuration options prior to sending commands to the operating system or memory controller. The hypervisor in these cases handles any address redirection and offsets from the real hardware addresses such that all servers virtualized partitions operating system all see real memory location 0000 as the first memory location. 
   A service processor ( FIG. 1   101 ) configures DIMM ( FIG. 1   106 ) as unavailable to the operating system so it is no longer used to place virtual memory or real memory pages. The service processor then powers off the DIMM slot for DIMM ( FIG. 1   106 ). This enables the ability to hot remove and replace the memory DIMM in slot ( FIG. 1   106 ). 
   At step  206 , a service technician physically removes and replaces the failed DIMM ( FIG. 1   106 ) with a new DIMM, which will be referred to as new DIMM or new memory from herein. For example, a service technician may request to power on the slot for the new DIMM and test the new memory unit. Such requests may be communicated using service processor interface command commonly available on a P-Series Hardware Management Console (HMC). 
   At step  210 , the new DIMM has power applied to it and logic contained on that DIMM runs a Basic Initialization Self Test (BIST) to determine if there are any immediate failures. At step  212 , if the BIST fails, the flow proceeds to the maintenance repair path at step  214  for a failed DIMM. Since this new DIMM was not under operating system control the running operating system is unaffected. If the BIST passes, at step  216 , control of DIMM is returned back to the service processor  101 , for example, via an interrupt being raised on the service processor wired net ( FIG. 1   100 ). The service processor begins to write and read test this DIMM. A test pattern and length of test may be determined based on the request. For example, a test pattern may be determined or generated based on length and amount of memory being tested. An example of a test may be to use a test pattern for a period of time. For instance, the service processor may use test pattern 1 to 10 hours such that the test pattern is 4 Gigabytes (assuming a 4 GB DIMM) of repeating test data in the form of 0×F0F0F0F0F0F0F0F0 followed by 0×FFFFFFFFFFFFFFFF followed by 0×0000000000000001. A timer may be set for 10 hours and the test data is then written to DIMM  106 . 
   At step  218 , a service processor reads the contents of new DIMM that was test written. At step  220 , the service processor compares to the read pattern to the known test pattern, that is, the test pattern that was used to write to the new memory at step  216 . At  220 , if the read pattern compares successfully to the written pattern, and the timer has not expired at  222 , the testing continues by repeating steps  216  and  218  until the timer expires or the compare is not successful. It should be noted that recoverable errors could occur during this step and may not be detected by this test. The normal logic for chipkill for a recoverable error maybe used and this resulting flow would then be repeated. If the test at step  220  fails, maintenance repair action for a failed memory DIMM may be followed at step  214 . Any known or will be known repair action for a failed memory DIMM may be followed. If the timer expired at step  222 , the write and read tests have completed. A service processor may then configure the new DIMM as available for the system at step  224 . This may or may not entail sending an initialization sequence to the memory DIMM depending on the architecture requirements. In other exemplary embodiments that have hardware memory mirroring the redundant DIMMS can be returned to use via hardware functionality. 
   A method, information processing system and computer readable medium allow for considerably extensive write and read testing of replaced memory DIMMS in a concurrent fashion. The write and read testing lengths and cycles can be set, for example, by an administrator or repair technician. This allows for “burn in” of the new memory DIMMS in their associated system installation environment. 
   The embodiments described above are illustrative examples and it should not be construed that the present invention is limited to these particular embodiments. Thus, various changes and modifications may be effective by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.