6.15. Event Management

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

Functions

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

6.15.1. Functions

__host__ cudaError_t cudaEventCreate(cudaEvent_t *event)

Creates an event object.

Creates an event object for the current device using cudaEventDefault.

Note

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

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Parameters: event – - Newly created event
Returns: cudaSuccess, cudaErrorInvalidValue, cudaErrorLaunchFailure, cudaErrorMemoryAllocation

__host__ cudaError_t cudaEventCreateWithFlags(cudaEvent_t *event, unsigned int flags)

Creates an event object with the specified flags.

Creates an event object for the current device 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.

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Parameters

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

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorLaunchFailure, cudaErrorMemoryAllocation

__host__ cudaError_t cudaEventDestroy(cudaEvent_t event)

Destroys an event object.

Destroys the event specified by event.

An event may be destroyed before it is complete (i.e., while cudaEventQuery() would return cudaErrorNotReady). In this case, the call does not block on completion of the event, and any associated resources will automatically be released asynchronously at completion.

Note

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

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Note

Use of the handle after this call is undefined behavior.

Note

Returns cudaErrorInvalidResourceHandle in the event of being passed NULL as the input event.

Parameters: event – - Event to destroy
Returns: cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure

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

Computes the elapsed time between events.

Computes the elapsed time between two events (in milliseconds with a resolution of around 0.5 microseconds). Note this API is not guaranteed to return the latest errors for pending work. As such this API is intended to serve as a elapsed time calculation only and polling for completion on the events to be compared should be done with cudaEventQuery instead.

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.

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Note

Returns cudaErrorInvalidResourceHandle in the event of being passed NULL as the input event.

Parameters

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

Returns

cudaSuccess, cudaErrorNotReady, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure, cudaErrorUnknown

__host__ cudaError_t cudaEventQuery(cudaEvent_t event)

Queries an event’s status.

Queries the status of all work currently captured by event. See cudaEventRecord() for details on what is captured by an event.

Returns cudaSuccess if all captured work has been completed, or cudaErrorNotReady if any captured work is incomplete.

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.

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Note

Returns cudaErrorInvalidResourceHandle in the event of being passed NULL as the input event.

Parameters: event – - Event to query
Returns: cudaSuccess, cudaErrorNotReady, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure

__host__ cudaError_t cudaEventRecord(cudaEvent_t event, cudaStream_t stream = 0)

Records an event.

Captures in event the contents of stream at the time of this call. event and stream must be on the same CUDA context. Calls such as cudaEventQuery() or cudaStreamWaitEvent() will then examine or wait for completion of the work that was captured. Uses of stream after this call do not modify event. See note on default stream behavior for what is captured in the default case.

cudaEventRecord() can be called multiple times on the same event and will overwrite the previously captured state. Other APIs such as cudaStreamWaitEvent() use the most recently captured state at the time of the API call, and are not affected by later calls to cudaEventRecord(). Before the first call to cudaEventRecord(), an event represents an empty set of work, so for example cudaEventQuery() would return cudaSuccess.

Note

This function uses standard default stream semantics.

Note

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

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Note

Returns cudaErrorInvalidResourceHandle in the event of being passed NULL as the input event.

Parameters

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

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure

__host__ cudaError_t cudaEventRecordWithFlags(cudaEvent_t event, cudaStream_t stream = 0, unsigned int flags = 0)

Records an event.

Captures in event the contents of stream at the time of this call. event and stream must be on the same CUDA context. Calls such as cudaEventQuery() or cudaStreamWaitEvent() will then examine or wait for completion of the work that was captured. Uses of stream after this call do not modify event. See note on default stream behavior for what is captured in the default case.

cudaEventRecordWithFlags() can be called multiple times on the same event and will overwrite the previously captured state. Other APIs such as cudaStreamWaitEvent() use the most recently captured state at the time of the API call, and are not affected by later calls to cudaEventRecordWithFlags(). Before the first call to cudaEventRecordWithFlags(), an event represents an empty set of work, so for example cudaEventQuery() would return cudaSuccess.

flags include:

cudaEventRecordDefault: Default event creation flag.
cudaEventRecordExternal: Event is captured in the graph as an external event node when performing stream capture.

Note

This function uses standard default stream semantics.

Note

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

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Note

Returns cudaErrorInvalidResourceHandle in the event of being passed NULL as the input event.

Parameters

event – - Event to record
stream – - Stream in which to record event
flags – - Parameters for the operation(See above)

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure

__host__ cudaError_t cudaEventSynchronize(cudaEvent_t event)

Waits for an event to complete.

Waits until the completion of all work currently captured in event. See cudaEventRecord() for details on what is captured by an event.

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.

Note

Note that this function may also return cudaErrorInitializationError, cudaErrorInsufficientDriver or cudaErrorNoDevice if this call tries to initialize internal CUDA RT state.

Note

Note that as specified by cudaStreamAddCallback no CUDA function may be called from callback. cudaErrorNotPermitted may, but is not guaranteed to, be returned as a diagnostic in such case.

Note

Returns cudaErrorInvalidResourceHandle in the event of being passed NULL as the input event.

Parameters: event – - Event to wait for
Returns: cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle, cudaErrorLaunchFailure