[vtk-developers] Proposal to add "vtkInfoMacro"

[David Gobbi]

Well, vtkImageReslice is probably not the best "speed" example any more, it
has become fat with all the features that I've added to it over the years
:)   And in the old days, a big reason for its speed was that it did some
bit-twiddling to work around the disastrously slow floor() operations on
old CPUs.

However, it is certainly true with modern computer architectures, with
their multiple cores and fast caches, doing _any_ application-level or
system-level operations within the algorithmic code causes a significant
performance hit, because that takes the CPU core out of the "zone" where it
can work at its full potential.

 - David

On Fri, Dec 12, 2014 at 5:12 PM, Berk Geveci <berk.geveci at kitware.com>
wrote:
>
> I'd be fine with it if the header is put into a higher level module such
> as GUISupport and has some examples demonstrating its purpose and some
> documentation providing a guide on how to use it. I would not agree to
> putting this at a place where it may encourage folks to use it in
> algorithms and other core functionality. As I mentioned previously, I
> already have the unpleasant job of ripping out a number of "convenience"
> functionality that are going to have significant impact on performance as
> we continue to multi-thread more algorithms. All of these features look
> harmless when initially added. Then they find their way into core
> functionality slowly but surely. When you are considering 200-way
> parallelism (which we are, since we are porting to Intel Xeon Phi already),
> any little bit makes a difference. Some simple examples:
>
> * Garbage collection
> * vtkDataArrayTemplate::DataChanged()
> * Abundant use of Modified()
> * Progress reporting
>
> Very nice and convenient feature. They may lead to a code running more
> slowly as more threads are added rather than scale up.
>
> I don't agree that misuse of such features would get caught in reviews.
> Very few reviewers are conscious of potential performance issues. Because
> very few developers are performance conscious at this point (Dave Gobbi
> excepted, he writes amazingly fast code, see image reslice).
>
> So this is not the time to pepper core classes with convenience
> functionality. It is time to simplify and come with very clear guidelines
> on what core classes and algorithms can and cannot do. Once the development
> community becomes more aware of these issues and our dashboards are able to
> catch performance regressions, we can relax some.
>
> Best,
> -berk
>
>
>
>
> On Fri, Dec 12, 2014 at 9:52 AM, David Gobbi <david.gobbi at gmail.com>
> wrote:
>>
>> However, I have reservations about putting this macro in vtkSetGet.h. If
>> it goes in its own header, then the chances of it being confused with
>> vtkDebugMacro are significantly reduced.
>>
>>  - David
>>
>>
>> On Fri, Dec 12, 2014 at 7:24 AM, Andras Lasso <lasso at queensu.ca> wrote:
>>
>>>  I completely agree with David. This is an application support feature.
>>> There are several examples for such features in VTK, including QVTKWidget
>>> or vtkOutputWindow::DisplayText(). These are not meant to be used in VTK
>>> library itself (other than examples and tests) but in VTK-based
>>> applications. They make the life of application developers easier, allow
>>> standardization, reduces code/feature duplication.
>>>
>>>
>>>
>>> Adding the macro has negligible impact on VTK but would help application
>>> developers.
>>>
>>>
>>>
>>> Andras
>>>
>>>
>>>
>>>
>>>
>>> *From:* David Gobbi [mailto:david.gobbi at gmail.com]
>>> *Sent:* Friday, December 12, 2014 09:16
>>> *To:* vtk-developers at vtk.org
>>> *Cc:* Jean-Christophe Fillion-Robin; Berk Geveci; Andras Lasso
>>> *Subject:* Re: [vtk-developers] Proposal to add "vtkInfoMacro"
>>>
>>>
>>>
>>> On the one hand, I can see that it is useful to have a message macro
>>> that doesn't require a debug build.  In my own apps, I often write
>>> app-specific classes that are derived from vtkObject and this is a macro
>>> that I might use from time to time.  Unlike Berk, I'm not all that worried
>>> that it might be abused.  For VTK, we have code review.
>>>
>>>
>>>
>>> On the other hand, I don't think we have a use case for this within VTK
>>> itself, it would be there purely to serve external VTK classes and apps.
>>> And people who need this feature could simply put this macro (or a similar
>>> one) in their own header files.
>>>
>>>
>>>
>>> Summary: this is a convenience feature, IMHO a mostly harmless one, and
>>> one that I might use.
>>>
>>>
>>>
>>>  - David
>>>
>>>
>>>
>>>
>>>
>>> On Fri, Dec 12, 2014 at 6:27 AM, Berk Geveci <berk.geveci at kitware.com>
>>> wrote:
>>>
>>>  I disagree with this change. There is no compelling VTK specific
>>> example for why this is needed. The examples are all from Slicer - which to
>>> me says that they can be implemented in Slicer.
>>>
>>>
>>>
>>> Adding a logging functionality without clear guidelines on how to use it
>>> is dangerous. It can lead to folks using it for debugging in performance
>>> critical sections and since it is not compiled out in Release builds, it
>>> can lead to significant performance issues, specially in multi-threaded
>>> code. As it is, there are lot of minor issues like this that we will have
>>> to go and clean up (progress being one of them).
>>>
>>>
>>>
>>> The main use case seems to be tracking interaction/workflow changes. My
>>> suggestion is to employ a method appropriate to that. For example, events
>>> and listeners.
>>>
>>>
>>>
>>> Best,
>>>
>>> -berk
>>>
>>>
>>>
>>>
>>>
>>> On Thu, Dec 11, 2014 at 12:06 PM, Jean-Christophe Fillion-Robin <
>>> jchris.fillionr at kitware.com> wrote:
>>>
>>>     Hi Folks,
>>>
>>> While developing 3D Slicer, we created a macro named
>>>
>>>                                           vtkInfoMacro
>>>
>>> similar to "vtkErrorMacro/vtkDebugMacro/vtkWarningMacro".
>>>
>>>   We would like to contribute it back to VTK core.
>>>
>>>
>>>
>>>  The associated topic is:
>>>
>>>                       http://review.source.kitware.com/#/c/18385/
>>>
>>>  It would be great to get feedback before moving forward.
>>>
>>> Thanks
>>>
>>> Jc
>>>
>>>
>>
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