mirror of
https://gitlab.kitware.com/vtk/vtk-m
synced 2024-10-05 09:59:12 +00:00
5b8c282e9f
These changes complete the using part of the guide.
43 lines
2.8 KiB
ReStructuredText
43 lines
2.8 KiB
ReStructuredText
==============================
|
|
Timers
|
|
==============================
|
|
|
|
.. index:: timer
|
|
|
|
It is often the case that you need to measure the time it takes for an operation to happen.
|
|
This could be for performing measurements for algorithm study or it could be to dynamically adjust scheduling.
|
|
|
|
Performing timing in a multi-threaded environment can be tricky because operations happen asynchronously.
|
|
To ensure that accurate timings can be made, |VTKm| provides a :class:`vtkm::cont::Timer` class to provide an accurate measurement of operations that happen on devices that |VTKm| can use.
|
|
By default, :class:`vtkm::cont::Timer` will time operations on all possible devices.
|
|
|
|
The timer is started by calling the :func:`vtkm::cont::Timer::Start` method.
|
|
The timer can subsequently be stopped by calling :func:`vtkm::cont::Timer::Stop`.
|
|
The time elapsed between calls to :func:`vtkm::cont::Timer::Start` and :func:`vtkm::cont::Timer::Stop` (or the current time if :func:`vtkm::cont::Timer::Stop` was not called) can be retrieved with a call to the :func:`vtkm::cont::Timer::GetElapsedTime` method.
|
|
Subsequently calling :func:`vtkm::cont::Timer::Start` again will restart the timer.
|
|
|
|
.. load-example:: Timer
|
|
:file: GuideExampleTimer.cxx
|
|
:caption: Using :class:`vtkm::cont::Timer`.
|
|
|
|
.. commonerrors::
|
|
Some device require data to be copied between the host CPU and the device.
|
|
In this case you might want to measure the time to copy data back to the host.
|
|
This can be done by "touching" the data on the host by getting a control portal.
|
|
|
|
The |VTKm| :class:`vtkm::cont::Timer` does its best to capture the time it takes for all parallel operations run between calls to :func:`vtkm::cont::Timer::Start` and :func:`vtkm::cont::Timer::Stop` to complete.
|
|
It does so by synchronizing to concurrent execution on devices that might be in use.
|
|
|
|
.. commonerrors::
|
|
Because :class:`vtkm::cont::Timer` synchronizes with devices (essentially waiting for the device to finish executing), that can have an effect on how your program runs.
|
|
Be aware that using a :class:`vtkm::cont::Timer` can itself change the performance of your code.
|
|
In particular, starting and stopping the timer many times to measure the parts of a sequence of operations can potentially make the whole operation run slower.
|
|
|
|
By default, :class:`vtkm::cont::Timer` will synchronize with all active devices.
|
|
However, if you want to measure the time for a specific device, then you can pass the device adapter tag or id to :class:`vtkm::cont::Timer`'s constructor.
|
|
You can also change the device being used by passing a device adapter tag or id to the :func:`vtkm::cont::Timer::Reset` method.
|
|
A device can also be specified through an optional argument to the :func:`vtkm::cont::Timer::GetElapsedTime` method.
|
|
|
|
.. doxygenclass:: vtkm::cont::Timer
|
|
:members:
|