SYSTEM ENABLING TRANSACTIONAL MEMORY AND PREDICTION-BASED TRANSACTION EXECUTION METHOD

• US 20090292884A1
• Filed: 05/08/2009
• Published: 11/26/2009
• Est. Priority Date: 05/23/2008
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Hall, Charles Brian, Liang, Zhi Yong, Wang, Yan Qi, Wang, Hua Yong, Shen, Xiao Wei
• Granted Patent: US 8,799,590 B2
• Time in Patent Office: Days
• US Class Current: 711/147
• CPC Class Codes: G06F 2209/507 Low-level
• CPC Class Codes: G06F 9/30087 Synchronisation or serialisation instructions
• CPC Class Codes: G06F 9/30189 according to execution mode, e.g. mode flag
• CPC Class Codes: G06F 9/3834 Maintaining memory consistency
• CPC Class Codes: G06F 9/3842 Speculative instruction execution
• CPC Class Codes: G06F 9/467 Transactional memory G06F9/528 takes precedence
• CPC Class Codes: G06F 9/528 by using speculative mechanisms

Abstract

This invention provides a system enabling Transactional Memory with overflow prediction mechanism, comprising: prediction unit for predicting the mode for the next execution of a transaction based on the final status of the previous execution of the transaction; execution unit for executing the transaction in the execution mode predicted by the prediction unit, wherein the execution mode comprises overflow mode and non-overflow made. According to this invention, before a transaction is executed, it is predicted whether or not the transaction will overflow, and therefore, the execution of the transaction which is necessary to determine whether or not an overflow will occur is saved and the system performance can be improved.

Claims

1. A system enabling Transactional Memory comprising:

a prediction unit for predicting the mode for the next execution of a transaction based on the final status of the preceding execution of the transaction;

an execution unit for executing the transaction in the mode predicted by the prediction unit, wherein the mode includes overflow mode and non-overflow mode.

2. The system enabling Transactional Memory according to claim 1, wherein as to a transaction executed in non-overflow mode,

if an overflow occurs during its execution, the mode for the next execution of the transaction is predicted as overflow mode by the prediction unit;

otherwise, the mode for the next execution of the transaction is predicted as non-overflow mode.

3. The system enabling Transactional Memory according to claim 2, further comprising:

a transaction write buffer for temporarily storing the speculative data of the transaction during the execution of the transaction in non-overflow mode by the execution unit and for recording data addresses of write operations inside the transaction during the execution of the transaction in overflow mode by the execution unit.

4. The system enabling Transactional Memory according to claim 3, wherein as to a transaction executed in overflow mode,

if the transaction write buffer has enough space to hold all the data addresses of the write operations inside the transaction during the execution of the transaction, the mode for the next execution of the transaction is predicted as non-overflow mode by the prediction unit;

otherwise, the mode for the next execution of the transaction is predicted as overflow mode by the prediction unit.

5. The system enabling Transactional Memory according to claim 3, further comprising:

a transaction read buffer for recording data address of read operations inside the transaction during the execution of the transaction by the execution unit;

wherein as to a transaction executed in overflow mode, if the transaction read buffer does not have space enough to hold all the data addresses of the read operations inside the transaction during the execution of the transaction, the mode for the next execution of the transaction is predicted as overflow mode by the prediction unit.

6. The system enabling Transactional Memory according to claim 2, wherein as to a transaction executed in non-overflow mode, if an overflow occurs during the execution of the transaction, the prediction unit further predicts the number of times N the transaction will be executed in overflow mode, and after the next N executions of the transaction in overflow mode, the mode for the next execution is predicted as non-overflow mode by the prediction unit.

7. The system enabling Transactional Memory according to claim 6, wherein when the transaction overflows,

if the mode of the last execution of the transaction is non-overflow mode, a minimum value N_min, which is a power of 2, is predicted as the number of times N the transaction will be executed in overflow mode;

and

if the mode of the last execution of the transaction is overflow mode, the prediction unit doubles the number of the times N predicted at the end of the last execution of the transaction as the number of times the transaction will be executed in overflow mode.

8. The system enabling Transactional Memory according to claim 1, further comprising:

a status register for storing the execution mode indicated by the execution unit;

a storage unit for writing data into a cache or the write buffer;

a load unit for reading data from the cache or the transaction write buffer; and

a data flow controller for controlling the storage unit or the load unit to read or write data according to the execution mode stored in the status register.

9. The system enabling Transactional Memory according to claim 1, wherein the prediction unit comprises a lookup table for storing information indicating the execution mode of a transaction, and

the execution mode information stored in the lookup table is modified according to the final state of the execution of the transaction.

10. The system enabling Transactional Memory according to claim 9, wherein if the execution unit does not find in the lookup table the execution mode information corresponding to a transaction to be executed, the execution mode information corresponding to the transaction is created in the lookup table, in which the execution mode is set to non-overflow mode.

11. A transaction execution method based on prediction, comprising:

a prediction step for predicting the mode for the next execution of a transaction based on the final state of the previous execution of the transaction;

a execution step for executing the transaction in the execution mode predicted in the prediction step, wherein the execution mode includes overflow mode and non-overflow mode.

12. The transaction execution method according to claim 11, wherein the prediction step further comprises the following step of:

as to a transaction executed in non-overflow mode, predicting the mode for the next execution of the transaction as overflow mode if an overflow occurs in the execution;

otherwise, predicting the mode for the next execution of the transaction as non-overflow mode.

13. The transaction execution method according to claim 12, wherein the execution step comprises:

in overflow mode, recording in a transaction write buffer data addresses of write operations inside a transaction being executed.

14. The transaction execution method according to claim 13, wherein the prediction step further comprises:

as to a transaction executed in overflow mode, predicting the mode for the next execution of the transaction as non-overflow mode if the transaction write buffer is sufficient for holding all the data addresses of the write operations of the transaction during the execution of the transaction, otherwise, predicting the mode for the next execution of the transaction as overflow mode.

15. The transaction execution method according to claim 13, wherein the execution step further comprises:

recording the data addresses of read operations inside the transaction in a transaction read buffer; and

the prediction step further comprises;

as to a transaction executed in overflow mode, predicting the mode for the next execution of the transaction as overflow mode if the transaction read buffer is not sufficient for holding all the data addresses of the read operations inside the transaction during the execution of the transaction.

16. The transaction execution method according to claim 12, wherein the prediction step further comprises:

as to a transaction executed in non-overflow mode, further predicting the number of times N the transaction will be executed in overflow mode if an overflow occurs during the execution of the transaction, and after the next N executions of the transaction in overflow mode, predicting the mode for the next execution of the transaction as non-overflow mode.

17. The transaction execution method according to claim 16, wherein when the transaction overflows,

if the mode of the last execution of the transaction is non-overflow mode, a minimum value N_min, which is a power of 2, is predicted as the number of times N the transaction will be executed in overflow mode;

and

if the mode for the last execution of the transaction is overflow mode, the number of times N predicted at the end of the last execution is doubled, and predicted as the number of times the transaction will be executed in overflow mode.

18. The transaction execution method according to claim 11, wherein the execution step further comprises:

storing the execution mode information;

executing store or load operations inside the transaction according to the stored execution mode information.

19. The transaction execution method according to claim 11, wherein the prediction step comprises:

storing information indicating the execution mode of a transaction in a lookup table; and

modifying the execution mode information stored in the lookup table according to the final status of the execution of the transaction.

20. The transaction execution method according to claim 19, wherein if the execution mode information corresponding to a transaction to be executed is not found in the lookup table, the execution mode information corresponding to the transaction is created in the lookup table, in which the execution mode is set to non-overflow mode.