CUDA Runtime API :: CUDA Toolkit Documentation

3.5. Event Management

This section describes the event management functions of the CUDA runtime application programming interface.

Functions

cudaError_t cudaEventCreate ( cudaEvent_t* event ): Creates an event object.
cudaError_t cudaEventCreateWithFlags ( cudaEvent_t* event, unsigned int flags ): Creates an event object with the specified flags.
cudaError_t cudaEventDestroy ( cudaEvent_t event ): Destroys an event object.
cudaError_t cudaEventElapsedTime ( float* ms, cudaEvent_t start, cudaEvent_t end ): Computes the elapsed time between events.
cudaError_t cudaEventQuery ( cudaEvent_t event ): Queries an event's status.
cudaError_t cudaEventRecord ( cudaEvent_t event, cudaStream_t stream = 0 ): Records an event.
cudaError_t cudaEventSynchronize ( cudaEvent_t event ): Waits for an event to complete.

Functions

cudaError_t cudaEventCreate ( cudaEvent_t* event )

Creates an event object.

Parameters

event: - Newly created event

Returns

cudaSuccess, cudaErrorInitializationError, cudaErrorInvalidValue, cudaErrorLaunchFailure, cudaErrorMemoryAllocation

Description

Creates an event object using cudaEventDefault.

Note:

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

cudaError_t cudaEventCreateWithFlags ( cudaEvent_t* event, unsigned int flags )

Creates an event object with the specified flags.

Parameters

event: - Newly created event
flags: - Flags for new event

Returns

cudaSuccess, cudaErrorInitializationError, cudaErrorInvalidValue, cudaErrorLaunchFailure, cudaErrorMemoryAllocation

Description

Creates an event object with the specified flags. Valid flags include:

cudaEventDefault: Default event creation flag.
cudaEventBlockingSync: Specifies that event should use blocking synchronization. A host thread that uses cudaEventSynchronize() to wait on an event created with this flag will block until the event actually completes.
cudaEventDisableTiming: Specifies that the created event does not need to record timing data. Events created with this flag specified and the cudaEventBlockingSync flag not specified will provide the best performance when used with cudaStreamWaitEvent() and cudaEventQuery().
cudaEventInterprocess: Specifies that the created event may be used as an interprocess event by cudaIpcGetEventHandle(). cudaEventInterprocess must be specified along with cudaEventDisableTiming.

Note:

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

cudaError_t cudaEventDestroy ( cudaEvent_t event )

Destroys an event object.

Parameters

event: - Event to destroy

Returns

cudaSuccess, cudaErrorInitializationError, cudaErrorInvalidValue, cudaErrorLaunchFailure

Description

Destroys the event specified by event.

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

Note:

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

cudaError_t cudaEventElapsedTime ( float* ms, cudaEvent_t start, cudaEvent_t end )

Computes the elapsed time between events.

Parameters

ms: - Time between start and end in ms
start: - Starting event
end: - Ending event

Returns

cudaSuccess, cudaErrorNotReady, cudaErrorInvalidValue, cudaErrorInitializationError, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure

Description

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 cudaEventRecord() 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 cudaEventRecord() has not been called on either event, then cudaErrorInvalidResourceHandle is returned. If cudaEventRecord() has been called on both events but one or both of them has not yet been completed (that is, cudaEventQuery() would return cudaErrorNotReady on at least one of the events), cudaErrorNotReady is returned. If either event was created with the cudaEventDisableTiming flag, then this function will return cudaErrorInvalidResourceHandle.

Note:

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

cudaError_t cudaEventQuery ( cudaEvent_t event )

Queries an event's status.

Parameters

event: - Event to query

Returns

cudaSuccess, cudaErrorNotReady, cudaErrorInitializationError, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure

Description

Query the status of all device work preceding the most recent call to cudaEventRecord() (in the appropriate compute streams, as specified by the arguments to cudaEventRecord()).

If this work has successfully been completed by the device, or if cudaEventRecord() has not been called on event, then cudaSuccess is returned. If this work has not yet been completed by the device then cudaErrorNotReady is returned.

For the purposes of Unified Memory, a return value of cudaSuccess is equivalent to having called cudaEventSynchronize().

Note:

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

cudaError_t cudaEventRecord ( cudaEvent_t event, cudaStream_t stream = 0 )

Records an event.

Parameters

event: - Event to record
stream: - Stream in which to record event

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorInitializationError, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure

Description

Records an event. See note about NULL stream behavior. Since operation is asynchronous, cudaEventQuery() or cudaEventSynchronize() must be used to determine when the event has actually been recorded.

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

Note:

This function uses standard NULL stream semantics.
Note that this function may also return error codes from previous, asynchronous launches.

cudaError_t cudaEventSynchronize ( cudaEvent_t event )

Waits for an event to complete.

Parameters

event: - Event to wait for

Returns

cudaSuccess, cudaErrorInitializationError, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure

Description

Wait until the completion of all device work preceding the most recent call to cudaEventRecord() (in the appropriate compute streams, as specified by the arguments to cudaEventRecord()).

If cudaEventRecord() has not been called on event, cudaSuccess is returned immediately.

Waiting for an event that was created with the cudaEventBlockingSync flag will cause the calling CPU thread to block until the event has been completed by the device. If the cudaEventBlockingSync 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.