<div dir="ltr">A few comments:<div><br></div><div>* I support the path David wants to take. We flushed this out over several months in collaboration with a Google Summer of Code student. It is the best transition strategy given that we have several moving components (see below).</div><div><br></div><div>* The Simple backend of vtkSMPTools is only there for debugging. Helgrind produces lots of false positives when using TBB so I developed the Simple backend for use with Helgrind. It is not a production backend and pretty much sucks. Now that we haven an OpenMP backend that can be used with Helgrind, Simple must die. I don't see a reason to deprecate it first since it is there only for debugging. This is clearly documented in the PDF will pointed to.</div><div><br></div><div>* For compilers that do not support OpenMP 3.1, one can (and should) use TBB. TBB is the better backend anyway so I recommend it over OpenMP.</div><div><br></div><div>* We will not include TBB in VTK. It is an external dependency similarly to OpenGL & MPI. In the future, folks will have to get it or have OpenMP if they want any thread-level parallelism out of VTK. We need to discuss what "in the future" means.</div><div><br></div><div>* Posix threads, C++11 threads etc. are not the way to go. They are way too low level and require management of thread pools and such to get good scalability. Things that OpenMP and TBB already to well. In general, for the kind of parallel computing we want in VTK, the best tools are high level ones such as parallel for loops etc. Furthermore, OpenMP will be important where we want to get SIMD (vector) parallelism. Auto-vectorization is very imperfect. And there are no C++ primitives that help with SIMD in C++11.</div><div><br></div><div>* At one point, we will have to get rid of vtkMultiThreader (at least of its use in algorithms, it may still be useful for GUI threads and whatnot). Hopefully, by then OpenMP 3.1 or above will be universally supported so we can make it the default backend. If not though, we'll have to require that people use TBB.</div><div><br></div><div>Best,</div><div>-berk</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Feb 9, 2016 at 11:33 AM, Ken Martin <span dir="ltr"><<a href="mailto:ken.martin@kitware.com" target="_blank">ken.martin@kitware.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Echoing David's earlier comments it would seem like we would want a nice path to convert existing multithreaded algorithms to use vtkSMPTools knowing that vtkSMPTools would not slow down the existing algorithm. Doing<div><br></div><div>#if VTK_SMP_BACKEND == SLOW</div><div> use vtkMultithreader</div><div>#else</div><div> use vtkSMPTools</div><div>#endif<br><div><br></div><div>sounds odd. I did not read the pdf so if that is covered in there apologies.</div><div><br></div><div><br></div><div><br></div></div><div class="gmail_extra"><br><div class="gmail_quote"><div><div class="h5">On Tue, Feb 9, 2016 at 10:56 AM, David Gobbi <span dir="ltr"><<a href="mailto:david.gobbi@gmail.com" target="_blank">david.gobbi@gmail.com</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div class="h5"><div dir="ltr">Hi Sujin,<div><br></div><div>That sounds good. Even if the choice of backend is transparent as far as using vtkSMPTools is concerned, it's very nice to be able to report which backend was configured.</div><div><br></div><div> - David<br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Feb 9, 2016 at 8:46 AM, Sujin Philip <span dir="ltr"><<a href="mailto:sujin.philip@kitware.com" target="_blank">sujin.philip@kitware.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div><div>Hi Sean,<br><br></div>vtkSMPTools is a framework for implementing multi-threaded algorithms in VTK. It support several backends. The main ones are TBB and OpenMP. There are Kaapi and Simple backends which are no longer supported and will be removed soon. Finally, the default backend is Sequential which is just a single threaded implementation of the framework. After removal of the Kaapi and Simple backend, if you need multithreading support on Clang you would have to use TBB. The Sequential backend will be supported on all platforms.<br><br></div>David,<br><br>I have talked with Berk about this and I will soon make a change to have a compile time macro to check for SMP backend type. I will also finally remove Kaapi and Simple backend as part of this change.<br><br></div>Thanks<span><font color="#888888"><br></font></span></div><span><font color="#888888">Sujin<br><br></font></span></div><div><div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Feb 9, 2016 at 10:28 AM, Sean McBride <span dir="ltr"><<a href="mailto:sean@rogue-research.com" target="_blank">sean@rogue-research.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span>On Tue, 9 Feb 2016 09:13:48 -0500, Sujin Philip said:<br>
<br>
>Why would you want to continue using vtkMultiThreader when Sequential or<br>
>Simple is used? In fact, now that there is an openmp backend, we should be<br>
>removing simple. It was only there to ease debugging since tbb had very<br>
>complex back-traces. Openmp back-traces are much more readable. Do you want<br>
>the algorithm to be multithreaded even when Sequential is used?<br>
<br>
</span>I don't know the APIs you're discussing, so this comment is coming mostly from ignorance, but: are you talking about requiring OpenMP to build VTK? Clang has only very recently added OpenMP support, and IIRC it's not complete. Also, last I checked, Apple's fork of clang doesn't support it at all.<br>
<br>
Cheers,<span><font color="#888888"><br>
<span><font color="#888888"><br>
--<br>
____________________________________________________________<br>
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