[vtk-developers] Checking SMP backend at runtime/compiletime?

Wed Feb 10 09:54:28 EST 2016

Very good. Thank you for the clarification.

Andras

From: Moreland, Kenneth [mailto:kmorel at sandia.gov]
Sent: Wednesday, February 10, 2016 9:50 AM
To: Andras Lasso <lasso at queensu.ca>
Cc: Geveci, Berk (External Contact) <berk.geveci at kitware.com>; Ken Martin <ken.martin at kitware.com>; VTK Developers <vtk-developers at vtk.org>; David Gobbi <david.gobbi at gmail.com>
Subject: RE: [vtk-developers] Checking SMP backend at runtime/compiletime?

Andreas,

I am not a lawyer, so I make no claims to my expertise in this, but I'm pretty sure you should be ok. Looking at that same FAQ link you sent is this:

Intel® TBB is available under the common open-source software license, GPLv2 with the (libstdc++) runtime exception. Specifically, the Intel® TBB open-source license is exactly the same as that used by the libstdc++ in gcc 4.2.1 (and earlier). GPLv2 is the same license used for a variety of well-known OSS applications including MySQL, NetBeans, and the Linux kernel. - See more at: https://www.threadingbuildingblocks.org/faq/10#sthash.IQJJn2NB.dpuf

So, you if you feel comfortable compiling your code with gcc, you shod be fine.
-Ken

Sent from my iPad so blame autocorrect.

On Feb 9, 2016, at 5:14 PM, Andras Lasso <lasso at queensu.ca<mailto:lasso at queensu.ca>> wrote:
Intel TBB price: https://software.intel.com/en-us/intel-tbb/try-buy

Although the https://www.threadingbuildingblocks.org/faq/10 page tries to clarify dual licensing, it's still not fully clear for me if there is any catch in the open-source license.

Can you confirm that TBB in VTK can be used in a commercial software without any restrictions (paying licensing fees, disclosing source code, etc)?

Andras

From: Moreland, Kenneth [mailto:kmorel at sandia.gov]
Sent: February 9, 2016 6:32 PM
To: Andras Lasso <lasso at queensu.ca<mailto:lasso at queensu.ca>>; Geveci, Berk (External Contact) <berk.geveci at kitware.com<mailto:berk.geveci at kitware.com>>; Ken Martin <ken.martin at kitware.com<mailto:ken.martin at kitware.com>>
Cc: VTK Developers <vtk-developers at vtk.org<mailto:vtk-developers at vtk.org>>; David Gobbi <david.gobbi at gmail.com<mailto:david.gobbi at gmail.com>>
Subject: Re: [vtk-developers] Checking SMP backend at runtime/compiletime?

$700? TBB is open-source, GPLv2 with runtime exception: https://www.threadingbuildingblocks.org/licensing

-Ken

From: vtk-developers <vtk-developers-bounces at vtk.org<mailto:vtk-developers-bounces at vtk.org>> on behalf of Andras Lasso <lasso at queensu.ca<mailto:lasso at queensu.ca>>
Date: Tuesday, February 9, 2016 at 3:56 PM
To: "Geveci, Berk (External Contact)" <berk.geveci at kitware.com<mailto:berk.geveci at kitware.com>>, Ken Martin <ken.martin at kitware.com<mailto:ken.martin at kitware.com>>
Cc: VTK Developers <vtk-developers at vtk.org<mailto:vtk-developers at vtk.org>>, David Gobbi <david.gobbi at gmail.com<mailto:david.gobbi at gmail.com>>
Subject: [EXTERNAL] Re: [vtk-developers] Checking SMP backend at runtime/compiletime?

>we'll have to require that people use TBB.
Are you talking about Intel TBB - single license starting from $700? Or there are some free replacements?

For most of our projects current performance of VTK is already good enough and it is very important to not have any licensing cost or restrictions. So, I would prefer free vtkMultiThreader over expensive Intel TBB, regardless of speed improvements.

Andras

From: Berk Geveci<mailto:berk.geveci at kitware.com>
Sent: February 9, 2016 14:56
To: Ken Martin<mailto:ken.martin at kitware.com>
Cc: VTK Developers<mailto:vtk-developers at vtk.org>; David Gobbi<mailto:david.gobbi at gmail.com>
Subject: Re: [vtk-developers] Checking SMP backend at runtime/compiletime?

A few comments:

* 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).

* 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.

* 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.

* 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.

* 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.

* 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.

Best,
-berk

On Tue, Feb 9, 2016 at 11:33 AM, Ken Martin <ken.martin at kitware.com<mailto:ken.martin at kitware.com>> wrote:
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

#if VTK_SMP_BACKEND == SLOW
 use vtkMultithreader
#else
  use vtkSMPTools
#endif

sounds odd. I did not read the pdf so if that is covered in there apologies.

On Tue, Feb 9, 2016 at 10:56 AM, David Gobbi <david.gobbi at gmail.com<mailto:david.gobbi at gmail.com>> wrote:
Hi Sujin,

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.

 - David

On Tue, Feb 9, 2016 at 8:46 AM, Sujin Philip <sujin.philip at kitware.com<mailto:sujin.philip at kitware.com>> wrote:
Hi Sean,
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.
David,

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.
Thanks
Sujin

On Tue, Feb 9, 2016 at 10:28 AM, Sean McBride <sean at rogue-research.com<mailto:sean at rogue-research.com>> wrote:
On Tue, 9 Feb 2016 09:13:48 -0500, Sujin Philip said:

>Why would you want to continue using vtkMultiThreader when Sequential or
>Simple is used? In fact, now that there is an openmp backend, we should be
>removing simple. It was only there to ease debugging since tbb had very
>complex back-traces. Openmp back-traces are much more readable. Do you want
>the algorithm to be multithreaded even when Sequential is used?

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.

Cheers,

--
____________________________________________________________
Sean McBride, B. Eng                 sean at rogue-research.com<mailto:sean at rogue-research.com>
Rogue Research                        www.rogue-research.com<http://www.rogue-research.com>
Mac Software Developer              Montréal, Québec, Canada

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