Abstract: A system, which includes a processor that includes a plurality of cores, generates an address translation when there is a miss in a translation lookaside buffer (TLB). A hypervisor utilizes a translating load instruction that upon execution on the processor generates a data portion of a TLB entry. Execution of the translating load instruction utilizes information from a real-to-physical address translation table entry and information provided in the call to the translating load instruction to synthesize the data portion of a new virtual-to-physical translation table entry.

Abstract: One embodiment of the present invention provides a system that facilitates efficient join operations between a head thread and a speculative thread during speculative program execution, wherein the head thread executes program instructions and the speculative thread executes program instructions in advance of the head thread. The system operates by executing a primary version of a program using the head thread, and by executing a speculative version of the program using the speculative thread. When the head thread reaches a point in the program where the speculative thread began executing, the system performs a join operation between the head thread and the speculative thread. This join operation causes the speculative thread to act as a new head thread by switching from executing the speculative version of the program to executing the primary version of the program.

Abstract: Explicit software control is used for data speculations. The explicit software control is applied at selected locations in a computer program to provide the benefit of data speculation while eliminating the need for hardware to perform data speculation. A computer-based method first determines, via explicit software control, whether data speculation for an item, a variable, a pointer, an address, etc., is needed. Upon determining that data speculation for the item is needed, the data speculation is performed under explicit software control. Conversely, if the explicit software control determines that data speculation is not needed, e.g., the value of the item typically obtained by execution of a long latency instruction, is available, an original code segment is executed using an actual value of the item.

Abstract: One embodiment of the present invention provides a system that facilitates inter-processor communication and synchronization through a hardware message buffer, which includes a plurality of physical channels that are structured as queues for communicating between processors in a multiprocessor system. The system operates by receiving an instruction to perform a data transfer operation through the hardware message buffer, wherein the instruction specifies a virtual channel to which the data transfer operation is directed. Next, the system translates the virtual channel into a physical channel, and then performs the data transfer operation on the physical channel within the hardware message buffer. In one embodiment of the present invention, if the data transfer operation is a store operation and the physical channel is already full, the system returns status information indicating that the physical channel is too full to perform the store operation.

Abstract: One embodiment of the present invention provides a system that facilitates deferring execution of instructions with unresolved data dependencies as they are issued for execution in program order. During a normal execution mode, the system issues instructions for execution in program order. Upon encountering an unresolved data dependency during execution of an instruction, the system generates a checkpoint that can subsequently be used to return execution of the program to the point of the instruction. Next, the system executes subsequent instructions in an execute-ahead mode, wherein instructions that cannot be executed because of an unresolved data dependency are deferred, and wherein other non-deferred instructions are executed in program order.

Abstract: A system that suppresses duplicative prefetches for branch target cache lines. During operation, the system fetches a first cache line into in a fetch buffer. The system then prefetches a second cache line, which immediately follows the first cache line, into the fetch buffer. If a control transfer instruction in the first cache line has a target instruction which is located in the second cache line, the system determines if the control transfer instruction is also located at the end of the first cache line so that a corresponding delay slot for the control transfer instruction is located at the beginning of the second cache line. If so, the system suppresses a subsequent prefetch for a target cache line containing the target instruction because the target instruction is located in the second cache line which has already been prefetched.

Abstract: One embodiment of the present invention provides a system that fixes bit errors encountered during references to a cache memory. During execution of an application, the system performs a reference to the cache memory by retrieving a data item and an associated error-correcting code from the cache memory. Next, the system computes an error-correcting code from the retrieved data item and compares the computed error-correcting code with the associated error-correcting code. If the computed error-correcting code does not match the associated error-correcting code a bit error has occurred. In this case, the system stores an identifier for the reference in a register within a set of one or more registers associated with the cache memory, so that the bit error can be fixed at a later time. The system also allows the application to continue executing.

Abstract: One embodiment of the present invention provides a system that corrects bit errors in temporary results within a central processing unit (CPU). During operation, the system receives a temporary result during execution of an in-flight instruction. Next, the system generates a parity bit for the temporary result, and stores the temporary result and the parity bit in a temporary register within the CPU. Before the temporary result is committed to the architectural state of the CPU, the system checks the temporary result and the parity bit to detect a bit error. If a bit error is detected, the system performs a micro-trap operation to re-execute the instruction that generated the temporary result, thereby regenerating the temporary result. Otherwise, if a bit error is not detected, the system commits the temporary result to the architectural state of the CPU.

Abstract: One embodiment of the present invention provides a system that facilitates deferring execution of instructions with unresolved data dependencies as they are issued for execution in program order. During a normal execution mode, the system issues instructions for execution in program order. Upon encountering an unresolved data dependency during execution of an instruction, the system generates a checkpoint that can subsequently be used to return execution of the program to the point of the instruction. Next, the system executes subsequent instructions in an execute-ahead mode, wherein instructions that cannot be executed because of an unresolved data dependency are deferred, and wherein other non-deferred instructions are executed in program order.

Abstract: One embodiment of the present invention provides a system which performs simultaneous speculative threading. The system starts by executing instructions in normal execution mode using a first thread. Upon encountering a data-dependent stall condition, the first thread generates an architectural checkpoint and commences execution of instructions in execute-ahead mode. During execute-ahead mode, the first thread executes instructions that can be executed and defers instructions that cannot be executed into a deferred queue. When the data dependent stall condition has been resolved, the first thread generates a speculative checkpoint and continues execution in execute-ahead mode. At the same time, the second thread commences execution in a deferred mode, wherein the second thread executes instructions deferred by the first thread.

Abstract: One embodiment of the present invention provides a system which creates multiple checkpoints in a processor that supports speculative-execution. The system starts by issuing instructions for execution in program order during execution of a program in a normal-execution mode. Upon encountering a launch condition during an instruction which causes a processor to enter execute-ahead mode, the system performs an initial checkpoint and commences execution of instructions in execute-ahead mode. Upon encountering a predefined condition during execute-ahead mode, the system generates an additional checkpoint and continues to execute instructions in execute-ahead mode. Generating the additional checkpoint allows the processor to return to the additional checkpoint, instead of the previous checkpoint, if the processor subsequently encounters a condition that requires the processor to return to a checkpoint.

Abstract: One embodiment of the present invention provides a system that facilitates selectively unmarking load-marked cache lines during transactional program execution, wherein load-marked cache lines are monitored during transactional execution to detect interfering accesses from other threads. During operation, the system encounters a release instruction during transactional execution of a block of instructions. In response to the release instruction, the system modifies the state of cache lines, which are specially load-marked to indicate they can be released from monitoring, to account for the release instruction being encountered. In doing so, the system can potentially cause the specially load-marked cache lines to become unmarked. In a variation on this embodiment, upon encountering a commit-and-start-new-transaction instruction, the system modifies load-marked cache lines to account for the commit-and-start-new-transaction instruction being encountered.

Abstract: One embodiment of the present invention provides a system that facilitates selectively unmarking load-marked cache lines during transactional program execution, wherein load-marked cache lines are monitored during transactional execution to detect interfering accesses from other threads. During operation, the system encounters a release instruction during transactional execution of a block of instructions. In response to the release instruction, the system modifies the state of cache lines, which are specially load-marked to indicate they can be released from monitoring, to account for the release instruction being encountered. In doing so, the system can potentially cause the specially load-marked cache lines to become unmarked. In a variation on this embodiment, upon encountering a commit-and-start-new-transaction instruction, the system modifies load-marked cache lines to account for the commit-and-start-new-transaction instruction being encountered.

Abstract: One embodiment of the present invention provides a system which improves branch prediction accuracy in a processor that supports speculative-execution. During normal-execution mode, the system issues instructions in program order. Upon encountering a launch condition which causes a processor to enter a speculative-execution mode, the system performs a checkpoint and begins executing instructions in a speculative-execution mode. Upon encountering a branch instruction during speculative-execution mode, the system selects the subsequent instruction to be executed based on a current state of a branch predictor and does not update the current state of the branch predictor, thereby preventing the branch predictor from being incorrectly updated twice when re-executing the branch instruction after returning to normal-execution mode.

Abstract: One embodiment of the present invention provides a system that predicts a result produced by a section of code in order to support speculative program execution. The system begins by executing the section of code using a head thread in order to produce a result. Before the head thread produces the result, the system generates a predicted result to be used in place of the result. Next, the system allows a speculative thread to use the predicted result in speculatively executing subsequent code that follows the section of code. After the head thread finishes executing the section of code, the system determines if a difference between the predicted result and the result generated by the head thread has affected execution of the speculative thread. If so, the system executes the subsequent code again using the result generated by the head thread. If not, the system performs a join operation to merge state associated with the speculative thread with state associated with the head thread.

Abstract: One embodiment of the present invention provides a system that facilitates interleaved execution of a head thread and a speculative thread within a single processor pipeline. The system operates by executing program instructions using the head thread, and by speculatively executing program instructions in advance of the head thread using the speculative thread, wherein the head thread and the speculative thread execute concurrently through time-multiplexed interleaving in the single processor pipeline.

Abstract: A plurality of processors on a chip is operated in lockstep. A crossbar switch on the chip couples and decouples the plurality of processors to a plurality of banks in a level-two (L2) cache. As data is stored in a first bank of the L2 cache, the old data at that location is passed through the crossbar switch to a second bank of the L2 cache that is functioning as a first-in-first-out memory (FIFO). Thus, new data is cached at a location in the first bank of the level-two cache, i.e., stored, and old data, from that location, is logged in the second bank of the level-two cache. The logged data in the second bank is used to restore the first bank to a known prior state when necessary.

Abstract: A system that facilitates error correction within a register file in a central processing unit (CPU). During execution of an instruction by the CPU, the system retrieves a dataword and an associated syndrome from a source register in the register file. Next, the system uses information in the dataword and the associated syndrome to detect, and if necessary correct, an error in the dataword or associated syndrome. This error detection and correction takes place in parallel with using the dataword to perform a computational operation specified by the instruction. If an error is detected, the system prevents the instruction from performing a writeback to a destination register in the register file. The system also writes a corrected dataword to the source register in the register file. Next, the system flushes the instruction pipeline, and restarts execution of the instruction so that the corrected dataword is retrieved for the computational operation.

Abstract: One embodiment of the present invention provides a system that predicts a result produced by a section of code in order to support speculative program execution. The system begins by executing the section of code using a head thread in order to produce a result. Before the head thread produces the result, the system generates a predicted result to be used in place of the result. Next, the system allows a speculative thread to use the predicted result in speculatively executing subsequent code that follows the section of code. After the head thread finishes executing the section of code, the system determines if a difference between the predicted result and the result generated by the head thread has affected execution of the speculative thread. If so, the system executes the subsequent code again using the result generated by the head thread. If not, the system performs a join operation to merge state associated with the speculative thread with state associated with the head thread.

Abstract: One embodiment of the present invention supports execution of a start transactional execution (STE) instruction, which marks the beginning of a block of instructions to be executed transactionally. Upon encountering the STE instruction during execution of a program, the system commences transactional execution of the block of instructions following the STE instruction. Changes made during this transactional execution are not committed to the architectural state of the processor until the transactional execution successfully completes.