Tracing processing activity

1. Data processing circuitry comprising:

a processing element configured to perform processing activities;

a trace data store; and

trace circuitry to:

generate items of trace data indicative of processing activities of the processing element, each item of trace data comprising a header indicative of a nature of a corresponding processing activity, and

store the items of trace data in the trace data store;

the trace circuitry comprising detection circuitry to:

detect a condition relating to an outcome of a given processing activity for which items of trace data have been stored in the trace data store, said condition being a period since initiation of the given processing activity, and

selectively discard at least some of the stored items of trace data relating to the given processing activity, and retain the header of each discarded item of trace data, in dependence upon the period since initiation of the given processing activity being less than a threshold period when the given processing activity reaches a predetermined stage.

2. Data processing circuitry according to claim 1 , in which:

the trace data store is a buffer having an associated order of data item storage and an indicator to indicate a next available storage position, in the order of data item storage; and

the detection circuitry is configured to discard stored items of trace data relating to the given processing activity by setting the indicator to indicate, as a next available storage position, a storage position in the trace data store at which an item of trace data relating to the given processing activity is stored.

3. Data processing circuitry according to claim 2 , in which:

the detection circuitry is configured to discard all of the stored items of trace data relating to the given processing activity by setting the indicator to indicate, as a next available storage position, a first storage position in the order of data item storage at which an item of trace data relating to the given processing activity is stored.

4. Data processing circuitry according to claim 2 , in which the detection circuitry is configured to store, in response to initiation of a processing activity, a current state of the indicator.

5. Data processing circuitry according to claim 4 , in which the detection circuitry is configured to discard all the stored items of data trace relating to the given processing activity by setting the indicator to indicate, as a next available storage position, the indicator value stored in response to initiation of the given processing activity.

6. Data processing circuitry according to claim 2 , in which the trace data store is a circular buffer in which, when the indicator reaches a limit position in the order of data item storage, the indicator is adjusted so that a next available storage position is a preceding position in the order of data item storage.

7. Data processing circuitry according to claim 6 , in which the limit position is a last storage position in the trace data store.

8. Data processing circuitry according to claim 6 , in which the limit position is no more than a limit number of storage positions, in the order of data item storage, from a first storage position at which an item of trace data relating to the given processing activity is stored.

9. Data processing circuitry according to claim 6 , in which the preceding position is a first available storage position after, in the order of data item storage, stored items of trace data which were not discarded by the detection circuitry.

10. Data processing circuitry according to claim 1 , in which the predetermined stage is completion of the given processing activity.

11. Data processing circuitry according to claim 1 , in which the detection circuitry is configured to discard stored items of trace data relating to the given processing activity in response to a detection of successful completion of the given processing activity.

12. Data processing circuitry according to claim 1 , in which:

the processing element is configured to execute program instructions; and

the processing activities relate to the execution of groups of program instructions.

13. Data processing circuitry according to claim 1 , in which:

the processing element comprises logic circuitry to execute logical operations; and

the processing activities relate to the execution of one or more logical operations.

14. Data processing circuitry according to claim 1 , in which:

the processing element comprises circuitry to transfer data from a source to a destination; and

the processing activities relate to data transfer operations.

15. Trace apparatus comprising:

trace circuitry to:

generate items of trace data indicative of processing activities of a processing element, each said item of trace data comprising a header indicative of a nature of a corresponding processing activity, and

store the items of trace data in a trace data store;

the trace circuitry comprising detection circuitry to:

detect a condition relating to an outcome of a given processing activity for which items of trace data have been stored in the trace data store, said condition being a period since initiation of the given processing activity, and

selectively discard at least some of the stored items of trace data relating to the given processing activity, and retain the header of each discarded item of trace data, in dependence upon the period since initiation of the given processing activity being less than a threshold period when the given processing activity reaches a predetermined stage.

16. A method comprising:

generating items of trace data indicative of processing activities of a processing element, each said item of trace data comprising a header indicative of a nature of a corresponding processing activity;

storing the items of trace data in a trace data store;

detecting a condition relating to an outcome of a given processing activity for which items of trace data have been stored in the trace data store, said condition being a period since initiation of the given processing activity; and

selectively discarding at least some of the stored items of trace data relating to the given processing activity, and retaining the header of each discarded item of trace data, in dependence upon the period since initiation of the given processing activity being less than a threshold period when the given processing activity reaches a predetermined stage.