Communication between threads of multi-thread processor

• US 10,558,463 B2
• Filed: 06/03/2016
• Issued: 02/11/2020
• Est. Priority Date: 06/03/2016
• Status: Active Grant

• Current Assignee: Synopsys Incorporated
• Original Assignee: Synopsys Incorporated
• Inventors: Tran, Thang
• Primary Examiner(s): Partridge, William B
• Application Number:
  US15/172,885
• Publication Number:
  US 20170351518A1
• Time in Patent Office: 1,348 Days
• Field of Search: 712220
• CPC Class Codes: G06F 9/30101 Special purpose registers
• CPC Class Codes: G06F 9/30123 according to context, e.g. thread buffers
• CPC Class Codes: G06F 9/30189 according to execution mode, e.g. mode flag
• CPC Class Codes: G06F 9/3851 from multiple instruction streams, e.g. multistreaming
• CPC Class Codes: G06F 9/461 Saving or restoring of program or task context
• CPC Class Codes: G06F 9/544 Buffers; Shared memory; Pipes

Abstract

Embodiments of the present disclosure support hardware based thread switching in a multithreading environment. The thread switching is implemented on a multithread microprocessor by utilizing thread mailbox registers and other auxiliary registers that can be pre-programmed for hardware based thread switching. A set of mailbox registers can be allocated to each thread of a plurality of threads that can be executed in the microprocessor. A mailbox register in the set of mailbox registers comprises an identifier of a next thread of the plurality of threads to which an active thread switches based on a thread switch condition further indicated in the mailbox register. The auxiliary registers in the microprocessor can be used to configure a number of threads for simultaneous execution in the microprocessor, a priority for thread switching, and to store a program counter of each thread and states of registers of each thread.

Claims

1. A method in a microprocessor, comprising:

allocating a set of mailbox registers to each thread of a plurality of threads for execution in the microprocessor;

including, in a field of a mailbox register in the set of mailbox registers, an identifier of a next thread of the plurality of threads to be executed in the microprocessor upon thread switching;

switching execution of the thread to execution of the next thread based upon a thread switch condition indicated in the mailbox register and the identifier of the next thread;

setting a bit in a first field of a thread enable register to enable a corresponding thread of the plurality of threads in a simultaneous multithreading (SMT) mode, the corresponding thread enabling one or more other threads of the plurality of threads in the SMT mode; and

enabling or disabling a thread of each of the plurality of threads for coarse grain multithreading, based on a corresponding bit in a second field of the thread enable register.

2. The method of claim 1, further comprising:

transmitting an interrupt signal to a control processor of the microprocessor to configure the next thread in the field of the mailbox register; and

writing, by the control processor in response to the interrupt, content associated with the next thread to one or more registers of the microprocessor.

3. The method of claim 1, further comprising:

pushing the mailbox register of the thread back into a thread mailbox First-In First-Out (FIFO) register allocated to the plurality of threads upon switching from the thread to the next thread,

the thread mailbox FIFO register having a plurality of mailbox entries, each mailbox entry comprises the mailbox register allocated to one thread of the plurality of threads.

4. The method of claim 1, further comprising:

writing the thread into a memory of the microprocessor dedicated for thread switching; and

reading, based on the identifier of the next thread in the mailbox register, the next thread from the memory for execution of the next thread in the microprocessor.

5. The method of claim 1, further comprising:

configuring execution of one or more threads at a time in the microprocessor by setting at least one bit in a thread configuration register of the microprocessor;

configuring, in the thread configuration register, a total number of threads for execution in the microprocessor;

configuring, in the thread configuration register, a number of one or more simultaneous threads for execution in the microprocessor.

6. The method of claim 1, further comprising:

setting, in a third field of the thread enable register, a priority for thread switching.

7. The method of claim 6, further comprising:

performing thread switching, based on the priority for the thread switching, using either a round robin process or the identifier of the next thread in the mailbox register.

8. The method of claim 6, further comprising:

loading the mailbox register with the next thread based on the priority indicated in the thread enable register.

9. The method of claim 1, further comprising:

writing a program counter (PC) of the thread into a thread PC register associated with the thread, upon switching from the thread to the next thread; and

fetching instructions of the next thread based on a content of another PC register associated with the next thread, upon switching from the thread to the next thread.

10. The method of claim 9, further comprising:

modifying the thread PC register and the other thread PC register using an auxiliary interface of the microprocessor.

11. The method of claim 1, further comprising:

writing processor states of the thread into a thread processor states register associated with the thread, upon switching from the thread to the next thread; and

restoring processor states of the next thread by reading another thread processor states register associated with the next thread, upon switching from the thread to the next thread.

12. The method of claim 11, further comprising:

modifying the thread processor states register and the other thread processor states register using an auxiliary interface of the microprocessor.

13. The method of claim 1, wherein the thread switch condition comprises indication about one from a group consisting of:

thread switching based on Level-2 (L2) cache miss,

thread switching based on a timer,

thread switching based on a software interrupt (SWI) generated by the thread,

thread switching based on an interrupt, and

thread switching based on an event.

14. The method of claim 1, wherein the allocation of the set of mailbox registers to each thread of the plurality of threads comprises:

allocating the set of mailbox registers to each thread of the plurality of threads that simultaneously run in the microprocessor, and the method further comprising

configuring, in each mailbox register in the set of mailbox register, a condition for switching from that thread to another thread and an identifier of the other thread.

15. A microprocessor, comprising:

a set of mailbox registers allocated to each thread of a plurality of threads for execution in the microprocessor; and

one or more auxiliary registers allocated to one or more of the plurality of threads including a thread enable register allocated to the plurality of threads, wherein

a mailbox register in the set of mailbox registers allocated to that thread comprises an identifier of a next thread of the plurality of threads to which that thread switches based on a thread switch condition indicated in the mailbox register,

the one or more auxiliary registers configure at least one of;

a number of threads in the plurality of threads for execution in the microprocessor, a priority for thread switching, storing a program counter (PC) of each thread, or storing states of registers of each thread,

a bit in a first field of the thread enable register is set to enable a corresponding thread of the plurality of threads in a simultaneous multithreading (SMT) mode, the corresponding thread enabling one or more other threads of the plurality of threads for execution in the SMT mode, and

a thread of each of the plurality of threads is enabled or disabled for coarse grain multithreading, based on a corresponding bit in a second field of the thread enable register.

16. The microprocessor of claim 15, further comprising:

a thread mailbox First-In First-Out (FIFO) register allocated to the plurality of threads having a plurality of mailbox entries, each mailbox entry in the thread mailbox FIFO register comprises the mailbox register allocated to that thread of the plurality of threads.

17. The microprocessor of claim 16, further comprising:

circuitry configured to write a mailbox entry for a thread of the plurality of threads into the thread mailbox FIFO register, based on an instruction of the thread or an external source triggered by the threads.

18. The microprocessor of claim 17, wherein the circuitry is further configured to write the mailbox entry into the thread mailbox FIFO register by recycling the mailbox entry from the thread mailbox FIFO register.

19. The microprocessor of claim 16, further comprising:

circuitry configured to read, from the thread mailbox FIFO register, a mailbox entry comprising the mailbox register for a thread of the plurality of threads, wherein

the circuitry is further configured to determine, based on the thread switch condition indicated within the mailbox entry, whether condition for thread switching is satisfied, and

the circuitry is further configured to switch execution from the thread to the next thread based on the identifier of the next thread within the mailbox entry, if the condition for thread switching is satisfied.

20. The microprocessor of claim 15, further comprising:

a memory dedicated for thread switching, wherein the memory comprises instructions of the next thread based on the identifier of the next thread.

21. The microprocessor of claim 15, wherein the one or more auxiliary registers comprises:

a thread configuration register, at least one bit in the thread configuration register to configure execution of one or more threads at a time in the microprocessor,

a field of the thread configuration register comprising information about the number of threads for execution in the microprocessor; and

another field of the thread configuration register comprising information of a number of one or more simultaneous threads for execution in the microprocessor.

22. The microprocessor of claim 15, wherein

a third field of the thread enable register comprising information about the priority for thread switching.

23. The microprocessor of claim 15, wherein the one or more auxiliary registers comprise:

a thread program counter (PC) register allocated for each thread of the plurality of threads,

the thread PC register comprises a content of PC of that thread associated with the thread PC register, upon switching from that thread to the next thread, and

the thread PC register allocated for the next thread comprises instructions of the next thread.

24. The microprocessor of claim 15, wherein the one or more auxiliary registers comprise:

a thread processor states register to allocate for each thread of the plurality of threads,

the thread processor states register loaded with processor states of a current thread upon switching from the current thread to the next thread, and

the thread processor states register allocated for the next thread loaded with processor states of the next thread.

25. The microprocessor of claim 15, wherein the priority for thread switching defines thread switching in a round robin manner or thread switching based on the identification of the next thread in the mailbox register.

26. The microprocessor of claim 15, wherein the thread switch condition comprises indication about one from a group consisting of:

thread switching based on an interrupt,

thread switching based on Level-2 (L2) cache miss,

thread switching based on a timer, and

thread switching based on an event.

27. The microprocessor of claim 15, wherein:

the set of mailbox registers are allocated to each thread of the plurality of threads simultaneously running in the microprocessor, and

each mailbox register in the set of mailbox registers configures a condition for switching from that thread to another thread and an identifier of the other thread.