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2.12. Event Management

This section describes the event management functions of the low-level CUDA driver application programming interface.

Functions

CUresult cuEventCreate ( CUevent* phEvent, unsigned int  Flags )
Creates an event.
CUresult cuEventDestroy ( CUevent hEvent )
Destroys an event.
CUresult cuEventElapsedTime ( float* pMilliseconds, CUevent hStart, CUevent hEnd )
Computes the elapsed time between two events.
CUresult cuEventQuery ( CUevent hEvent )
Queries an event's status.
CUresult cuEventRecord ( CUevent hEvent, CUstream hStream )
Records an event.
CUresult cuEventSynchronize ( CUevent hEvent )
Waits for an event to complete.

Functions

CUresult cuEventCreate ( CUevent* phEvent, unsigned int  Flags )

Creates an event. Creates an event *phEvent with the flags specified via Flags. Valid flags include:

Note:

Note that this function may also return error codes from previous, asynchronous launches.

See also:

cuEventRecord, cuEventQuery, cuEventSynchronize, cuEventDestroy, cuEventElapsedTime

Parameters
phEvent
- Returns newly created event
Flags
- Event creation flags
CUresult cuEventDestroy ( CUevent hEvent )

Destroys an event. Destroys the event specified by hEvent.

In the case that hEvent has been recorded but has not yet been completed when cuEventDestroy() is called, the function will return immediately and the resources associated with hEvent will be released automatically once the device has completed hEvent.

Note:

Note that this function may also return error codes from previous, asynchronous launches.

See also:

cuEventCreate, cuEventRecord, cuEventQuery, cuEventSynchronize, cuEventElapsedTime

Parameters
hEvent
- Event to destroy
CUresult cuEventElapsedTime ( float* pMilliseconds, CUevent hStart, CUevent hEnd )

Computes the elapsed time between two events. Computes the elapsed time between two events (in milliseconds with a resolution of around 0.5 microseconds).

If either event was last recorded in a non-NULL stream, the resulting time may be greater than expected (even if both used the same stream handle). This happens because the cuEventRecord() operation takes place asynchronously and there is no guarantee that the measured latency is actually just between the two events. Any number of other different stream operations could execute in between the two measured events, thus altering the timing in a significant way.

If cuEventRecord() has not been called on either event then CUDA_ERROR_INVALID_HANDLE is returned. If cuEventRecord() has been called on both events but one or both of them has not yet been completed (that is, cuEventQuery() would return CUDA_ERROR_NOT_READY on at least one of the events), CUDA_ERROR_NOT_READY is returned. If either event was created with the CU_EVENT_DISABLE_TIMING flag, then this function will return CUDA_ERROR_INVALID_HANDLE.

Note:

Note that this function may also return error codes from previous, asynchronous launches.

See also:

cuEventCreate, cuEventRecord, cuEventQuery, cuEventSynchronize, cuEventDestroy

Parameters
pMilliseconds
- Time between hStart and hEnd in ms
hStart
- Starting event
hEnd
- Ending event
CUresult cuEventQuery ( CUevent hEvent )

Queries an event's status. Query the status of all device work preceding the most recent call to cuEventRecord() (in the appropriate compute streams, as specified by the arguments to cuEventRecord()).

If this work has successfully been completed by the device, or if cuEventRecord() has not been called on hEvent, then CUDA_SUCCESS is returned. If this work has not yet been completed by the device then CUDA_ERROR_NOT_READY is returned.

Note:

Note that this function may also return error codes from previous, asynchronous launches.

See also:

cuEventCreate, cuEventRecord, cuEventSynchronize, cuEventDestroy, cuEventElapsedTime

Parameters
hEvent
- Event to query
CUresult cuEventRecord ( CUevent hEvent, CUstream hStream )

Records an event. Records an event. If hStream is non-zero, the event is recorded after all preceding operations in hStream have been completed; otherwise, it is recorded after all preceding operations in the CUDA context have been completed. Since operation is asynchronous, cuEventQuery and/or cuEventSynchronize() must be used to determine when the event has actually been recorded.

If cuEventRecord() has previously been called on hEvent, then this call will overwrite any existing state in hEvent. Any subsequent calls which examine the status of hEvent will only examine the completion of this most recent call to cuEventRecord().

It is necessary that hEvent and hStream be created on the same context.

Note:

Note that this function may also return error codes from previous, asynchronous launches.

See also:

cuEventCreate, cuEventQuery, cuEventSynchronize, cuStreamWaitEvent, cuEventDestroy, cuEventElapsedTime

Parameters
hEvent
- Event to record
hStream
- Stream to record event for
CUresult cuEventSynchronize ( CUevent hEvent )

Waits for an event to complete. Wait until the completion of all device work preceding the most recent call to cuEventRecord() (in the appropriate compute streams, as specified by the arguments to cuEventRecord()).

If cuEventRecord() has not been called on hEvent, CUDA_SUCCESS is returned immediately.

Waiting for an event that was created with the CU_EVENT_BLOCKING_SYNC flag will cause the calling CPU thread to block until the event has been completed by the device. If the CU_EVENT_BLOCKING_SYNC flag has not been set, then the CPU thread will busy-wait until the event has been completed by the device.

Note:

Note that this function may also return error codes from previous, asynchronous launches.

See also:

cuEventCreate, cuEventRecord, cuEventQuery, cuEventDestroy, cuEventElapsedTime

Parameters
hEvent
- Event to wait for

CUDA Driver API (PDF) - CUDA Toolkit v5.5 (older) - Last updated May 11, 2013 - Send Feedback