Using a transactional execution mechanism to free up processor resources used by a busy-waiting thread

• US 7,395,418 B1
• Filed: 09/22/2005
• Issued: 07/01/2008
• Est. Priority Date: 09/22/2005
• Status: Active Grant

• Current Assignee: Oracle America, Inc. (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Caprioli, Paul, Mesard, Wayne
• Primary Examiner(s): Li; Aimee J
• Application Number:
  US11/234,669
• Time in Patent Office: 1,013 Days
• Field of Search: 712/228, 712/229
• US Class Current: 712/228
• CPC Class Codes: G06F 9/3004 to perform operations on memory
• CPC Class Codes: G06F 9/3005 to perform operations for flow control
• CPC Class Codes: G06F 9/30087 Synchronisation or serialisation instructions
• CPC Class Codes: G06F 9/3009 Thread control instructions
• CPC Class Codes: G06F 9/30181 Instruction operation extension or modification
• CPC Class Codes: G06F 9/30189 according to execution mode, e.g. mode flag
• CPC Class Codes: G06F 9/3842 Speculative instruction execution
• CPC Class Codes: G06F 9/3851 from multiple instruction streams, e.g. multistreaming
• CPC Class Codes: G06F 9/3863 using multiple copies of the architectural state, e.g. shadow registers
• CPC Class Codes: G06F 9/3885 using a plurality of independent parallel functional units
• CPC Class Codes: G06F 9/467 Transactional memory G06F9/528 takes precedence
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

A technique for improving the performance of a system that supports simultaneous multi-threading (SMT). When a first thread encounters a halt sequence, the system starts a transactional memory operation by generating a checkpoint and entering a transactional-execution mode. Next, the system loads from a mailbox address associated with the halt sequence. The system then stalls execution of the first thread, so that the first thread does not execute instructions within the halt sequence, thereby freeing up processor resources for other threads. To terminate the halt sequence, a second thread stores to the mailbox address, which causes a transactional-memory mechanism within the processor to detect an interference with the previous load from the mailbox address by the first thread and which causes the first thread to exit from the halt sequence. The system then continues executing instructions following the halt sequence.

Claims

1. A method for improving the performance of a processor that supports speculative execution, wherein when a first thread encounters a halt sequence which is used by the first thread to wait for data that is to be generated by a second thread, the method comprises:

starting a transactional memory operation by generating a checkpoint and entering transactional-execution mode, wherein instructions are speculatively executed but results are not committed to the architectural state of the processor until the transaction completes without interference;

loading from a mailbox address associated with the halt sequence so that a transactional memory system can detect a subsequent interference with the load from the mailbox address, wherein the subsequent interference with the load from the mailbox address indicates that the halt sequence is to be terminated; and

while executing in a speculative-execution mode, stalling execution of the first thread, so that the processor does not execute instructions within the halt sequence, thereby freeing up processor resources for other threads;

wherein when the second thread has completed generating the data required by the first thread, the second thread performs a store operation to the mailbox address and a transactional-memory mechanism within the processor terminates the halt sequence by;

detecting an interference with the load from the mailbox address;

exiting the halt sequence; and

continuing execution of instructions following the halt sequence.

2. The method of claim 1, wherein stalling execution of the first thread involves executing a speculation-barrier instruction, wherein during transactional-execution mode, the speculation-barrier instruction prevents the first thread from speculatively executing subsequent instructions.

3. The method of claim 2, wherein the speculation-barrier instruction prevents the halt sequence from committing the transactional-memory operation.

4. The method of claim 1, wherein the halt sequence is implemented as:

a system call;

a library function;

or

a macro.

5. The method of claim 1, wherein the second thread terminates the halt sequence for the first thread after calculating a result required by the first thread.

6. An apparatus for improving the performance of a processor that supports speculative execution, comprising:

an processing mechanism configured such that when a first thread encounters a halt sequence which is used by the first thread to wait for data that is to be generated by a second thread, the processing mechanism;

starts a transactional memory operation using a transactional-memory mechanism which involves generating a checkpoint and entering transactional-execution mode, wherein instructions are speculatively executed but results are not committed to the architectural state of the processor until the transaction completes without interference;

loads from a mailbox address associated with the halt sequence so that a transactional memory system can detect a subsequent interference with the load from the mailbox address, wherein the subsequent interference with the load from the mailbox address indicates that the halt sequence is to be terminated; and

while executing in a speculative-execution mode, stalls execution of the first thread, so that the processor does not execute instructions within the halt sequence, thereby freeing up processor resources for other threads;

wherein when the second thread has completed generating the data required by the first thread, the second thread performs a store operation to the mailbox address and the transactional-memory mechanism within the processing mechanism is configured to;

detect an interference with the load from the mailbox address;

exit the halt sequence; and

to

continue execution of instructions following the halt sequence, thereby terminating the halt sequence.

7. The apparatus of claim 6, wherein stalling execution of the first thread involves executing a speculation-barrier instruction, wherein during transactional-execution mode, the speculation-barrier instruction prevents the first thread from speculatively executing subsequent instructions.

8. The apparatus of claim 7, wherein the speculation-barrier instruction prevents the halt sequence from committing the transactional-memory operation.

9. The apparatus of claim 6, wherein the halt sequence is implemented as:

a system call;

a library function;

or

a macro.

10. The apparatus of claim 6, wherein the second thread terminates the halt sequence for the first thread after calculating a result required by the first thread.

11. A computer system for improving the performance of a processor that supports speculative execution, comprising:

the processor;

a memory; and

a transactional-memory mechanism;

wherein when a first thread encounters a halt sequence which is used by the first thread to wait for data that is to be generated by a second thread, the processor is configured to;

start a transactional memory operation using the transactional-memory mechanism which involves generating a checkpoint and entering transactional-execution mode, wherein instructions are speculatively executed but results are not committed to the architectural state of the processor until the transaction completes without interference;

load from a mailbox address associated with the halt sequence so that a transactional memory system can detect a subsequent interference with the load from the mailbox address wherein the subsequent interference with the load from the mailbox address indicates that the halt sequence is to be terminated; and

while executing in a speculative-execution mode, stall execution of the first thread, so that the processor does not execute instructions within the halt sequence, thereby freeing up processor resources for other threads;

wherein when the second thread has completed generating the data required by the first thread, the second thread performs a store operation to the mailbox address and the transactional-memory mechanism within the processing mechanism is configured to;

detect an interference with the load from the mailbox address;

exit the halt sequence; and

to

continue execution of instructions following the halt sequence, thereby terminating the halt sequence.

12. The computer system of claim 11, wherein stalling execution of the first thread involves executing a speculation-barrier instruction, wherein during transactional-execution mode, the speculation-barrier instruction prevents the first thread from speculatively executing subsequent instructions.

13. The computer system of claim 12, wherein the speculation-barrier instruction prevents the halt sequence from committing the transactional-memory operation.

14. The computer system of claim 11, wherein the halt sequence is implemented as:

a system call;

a library function;

or

a macro.

15. The computer system of claim 11, wherein the second thread terminates the halt sequence for the first thread after calculating a result required by the first thread.