APPARATUS AND METHOD FOR PROCESSING THREADS REQUIRING RESOURCES

• US 20130247060A1
• Filed: 03/16/2012
• Published: 09/19/2013
• Est. Priority Date: 03/16/2012
• Status: Active Grant

• Current Assignee: Arm Ltd. (United Kingdom) (SoftBank Group Corp.)
• Original Assignee: Arm Ltd. (United Kingdom) (SoftBank Group Corp.)
• Inventors: MAKLJENOVIC, Nebojsa, JAMES, Benjamin Charles
• Granted Patent: US 8,966,494 B2
• Time in Patent Office: Days
• US Class Current: 718/104
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

A data processing apparatus has processing circuitry for processing threads using resources accessible to the processing circuitry. Thread handling circuitry handles pending threads which are waiting for resources required for processing. When a request is made for a resource which is not available, a lock is set to ensure that once the resource becomes available, the resource remains available until the lock is removed. This prevents other threads reallocating the resource. When a subsequent pending thread requests access to the same locked unavailable resource, the lock is transferred to that subsequent thread so that the latest thread accessing that resource is considered the lock owning thread. The lock is removed once the lock owning thread is ready for processing.

Claims

1. A data processing apparatus comprising:

processing circuitry configured to process processing threads using resources accessible to said processing circuitry;

thread handling circuitry configured to handle pending threads awaiting resources required for processing; and

resource checking circuitry configured to check whether at least one resource required by a pending thread from said thread handling circuitry is available, to forward said pending thread to said processing circuitry for processing if said at least one resource is available, and to request access to said at least one resource and retain said pending thread in said thread handling circuitry if said at least one resource is not available;

wherein;

said resource checking circuitry is configured to set a lock for an unavailable resource if said unavailable resource is requested for a pending thread and said unavailable resource is not already locked, and to set the pending thread for which the unavailable resource is requested as a lock owning thread for said unavailable resource, wherein a locked resource which becomes available remains available until the lock associated with the locked resource is removed;

on determining that a locked resource is unavailable for a subsequent pending thread which requires said locked resource and is not the current lock owning thread for said locked resource, said resource checking circuitry is configured to set said subsequent pending thread as the lock owning thread for said locked resource; and

said resource checking circuitry is configured to remove the lock associated with an available locked resource if the current lock owning thread for said available locked resource is forwarded to said processing circuitry for processing.

2. The data processing apparatus according to claim 1, wherein said resource checking circuitry is configured to retain the lock associated with said available locked resource if a pending thread which requires the available locked resource and which is not the current lock owning thread is forwarded to said processing circuitry for processing.

3. The data processing apparatus according to claim 1, wherein said locked resource is associated with a lock identifier identifying the current lock owning thread for said locked resource, and said resource checking circuitry is configured to set said subsequent pending thread as the lock owning thread by updating said lock identifier of said locked resource.

4. The data processing apparatus according to claim 3, wherein each pending thread is associated with a thread identifier, and said lock identifier comprises the thread identifier of the current lock owning thread.

5. The data processing apparatus according to claim 1, wherein said resource checking circuitry is configured to prevent said available locked resource becoming unavailable until the lock associated with said available locked resource has been removed.

6. The data processing apparatus according to claim 1, wherein said thread handling circuitry comprises a pipeline configured to perform pre-processing operations on said pending threads.

7. The data processing apparatus according to claim 6, wherein said pre-processing operations include determining which resources are required for said pending threads.

8. The data processing apparatus according to claim 6, wherein said resource checking circuitry is configured to check whether said at least one resource is available for a pending thread output from the pipeline, and if said at least one resource is not available, to return the pending thread to the start of the pipeline.

9. The data processing apparatus according to claim 1, wherein said thread handling circuitry comprises a thread buffer for buffering pending threads for which at least one resource is not yet available.

10. The data processing apparatus according to claim 9, wherein said thread buffer comprises a first-in first-out (FIFO) buffer, and said resource checking circuitry is configured to check whether said at least one resource has become available for a pending thread output from said FIFO buffer, and if said at least one resource is not available, to input said pending thread to said FIFO buffer.

11. The data processing apparatus according to claim 1, wherein said resources comprise data required for processing said pending threads.

12. The data processing apparatus according to claim 11, comprising a memory configured to store said data and a cache configured to cache a portion of said data stored in said memory, said cache comprising a plurality of cache storage locations.

13. The data processing apparatus according to claim 12, wherein said lock indicates that a cache storage location which has been allocated for storing data cannot be reallocated for storing other data until said lock has been removed.

14. The data processing apparatus according to claim 12, wherein said resource checking circuitry is configured to determine whether data required by a pending thread is present in said cache, and if not, to issue a request to fetch the required data from said memory and store said required data to a cache storage location of said cache and set a lock for said cache storage location.

15. The data processing apparatus according to claim 14, wherein if all cache storage locations of said cache are already allocated for storing data, then said resource checking circuitry is configured to reallocate a cache storage location for which no lock has been set for storing said required data.

16. The data processing apparatus according to claim 14, wherein if a lock has already been set for all cache storage locations of said cache, then said resource checking circuitry is configured to retain said pending thread in said thread handling circuitry without issuing said request to fetch the required data from said memory.

17. The data processing apparatus according to claim 1, wherein said processing circuitry comprises a graphics processor.

18. The data processing apparatus according to claim 17, wherein said resources include texture data and said processing threads comprise texture mapping threads for controlling said graphics processor to perform texture mapping operations using said texture data.

19. A data processing apparatus comprising:

processing means for processing processing threads using resources accessible to said processing circuitry;

thread handling means for handling pending threads awaiting resources required for processing; and

resource checking means for checking whether at least one resource required by a pending thread from said thread handling circuitry is available, for forwarding said pending thread to said processing means for processing if said at least one resource is available, and for requesting access to said at least one resource and retaining said pending thread in said thread handling means if said at least one resource is not available;

wherein;

said resource checking means is configured to set a lock for an unavailable resource if said unavailable resource is requested for a pending thread and said unavailable resource is not already locked, and to set the pending thread for which the unavailable resource is requested as a lock owning thread for said unavailable resource, wherein a locked resource which becomes available remains available until the lock associated with the locked resource is removed;

on determining that a locked resource is unavailable for a subsequent pending thread which requires said locked resource and is not the current lock owning thread for said locked resource, said resource checking means is configured to set said subsequent pending thread as the lock owning thread for said locked resource; and

said resource checking means is configured to remove the lock associated with an available locked resource if the current lock owning thread for said available locked resource is forwarded to said processing means for processing.

20. A method of processing data using a data processing apparatus comprising processing circuitry configured to process processing threads using resources accessible to said processing circuitry, and thread handling circuitry configured to handle pending threads awaiting resources required for processing;

said method comprising steps of;

(a) checking whether at least one resource required by a pending thread from said thread handling circuitry is available;

(b) if said at least one resource is available, then forwarding said pending thread to said processing circuitry for processing;

(c) if said at least one resource is not available, then;

(i) requesting access to said at least one resource for said pending thread and retaining said pending thread in said thread handling circuitry; and

(ii) setting a lock for said at least one resource, and setting the pending thread for which said at least one resource is requested as a lock owning thread for said at least one resource,

(d) checking whether a locked resource required by a subsequent pending thread from said thread handling circuitry is available, wherein a locked resource which becomes available remains available until the lock associated with the locked resource is removed;

(e) if said locked resource is unavailable and said subsequent pending thread is not the current lock owning thread for said locked resource, setting said subsequent pending thread as the lock owning thread for said locked resource; and

(f) if said locked resource is available and said subsequent pending thread is the current lock owning thread for said locked resource, forwarding said subsequent pending thread to said processing circuitry for processing and removing the lock associated with said locked resource.