PyOpenCL July 2012

pyopencl@tiker.net

10 participants
21 discussions

by Gregor Thalhammer

Dear Andreas, I am currently working on a cython based wrapper for the OpenCL FFT library from AMD: https://github.com/geggo/gpyfft For this I need to create a pyopencl Event instance from a cl_event returned by the library. I attached a patch against recent pyopencl that adds this possibility, similar to the from_cl_mem_as_int() method of the MemoryObject class. Could you please add this to pyopencl. Thanks for your help Gregor

7 years, 8 months

More good news

by Andreas Kloeckner

Hi all, now that we have a flexible scan, a lot of stuff becomes quite easy: http://documen.tician.de/pyopencl/array.html#sorting :) Performance isn't a dream yet, but I've also done exactly zero tuning. It manages 34 MKeys/s on Fermi and 42 MKeys/s on Tahiti. For comparison, numpy does about 10 MKeys/s on a CPU with a decent memory system. The CL code on the CPU achieves about 10 MKeys/s on 4+ cores, with the AMD implementation being 50% faster than Intel. (All this is on 32-bit integers.) If you've got some time to help tune this... :P But the real good news here is that a) this was pretty easy to put together on top of the existing scan primitive, and b) it actually yields code that works on quite a bunch of CL implementations. Hope you're finding this as exciting as me. :) Andreas

8 years, 7 months

Re: [PyOpenCL] Runtime error in Mountain Lion: symbol not found

by Andreas Kloeckner

Hi Bogdan, Bogdan Opanchuk <mantihor(a)gmail.com> writes: >> This is a bit mystifying. Where does that config option come from in >> your case? Can you check your siteconf.py or ~/.aksetup-defaults.py? If >> it's not coming from there, the default should pass the correct, unsplit >> (i.e. with comma) version to distutils. You can check this by putting >> >> print conf["LDFLAGS"] >> >> into setup.py before the call to setup(). If the correct thing is passed >> to distutils and it still comes out split, then that's a distutils >> issue. Otherwise, please report back, and we'll investigate. > > It seems that the incorrect value is indeed coming from distutils. If > I remove siteconf.py and just run "setup.py build", the flags are > correct (and siteconf.py is not created). Actually, this result means exactly the opposite--it means that distutils is innocent, and that something in PyOpenCL screws it up. Can you please run ./configure.py and check what ends up in siteconf.py? Thanks, Andreas

8 years, 8 months

Re: [PyOpenCL] How to pass an array of vectors in pyOpenCL

by Andreas Kloeckner

Hi there, J Diviney <justdivs(a)gmail.com> writes: > I've already posted this to stackoverflow, but then remembered that this > mailing list exists, so apologies if any of you have read it twice already. no worries, all good. > I'm moving a simulation into pyOpenCL and can't get my data access to work. > I'm trying to supply a 1D array of vectors (well, actually several arrays, > but the example I've included just uses one). > > Currently, the first few vectors are copied over just fine, but then the > data is simply not what I supplied. One possible problem that I see in your code is that float3s are actually laid out as four floats in memory. (You can see this using sizeof() in your kernel.) When dealing with vectors such as this, it's often most convenient to use pyopencl.array.vec.float3 as the dtype. HTH, Andreas

8 years, 8 months

How to pass an array of vectors in pyOpenCL

by J Diviney

Hi, I've already posted this to stackoverflow, but then remembered that this mailing list exists, so apologies if any of you have read it twice already. I'm moving a simulation into pyOpenCL and can't get my data access to work. I'm trying to supply a 1D array of vectors (well, actually several arrays, but the example I've included just uses one). Currently, the first few vectors are copied over just fine, but then the data is simply not what I supplied. I don't think I've posted here before, so apologies if any of the formatting/presentation is wrong. Also, I've just stripped out all the simulation code, so I realise this code is currently not actually doing anything, I just want to get the buffer passing correct. Thanks in advance. I've attached the kernel and the file that I'm calling it with.

8 years, 8 months

Segmented scan change

by Andreas Kloeckner

Hi all, if you've started using the new segmented scan implementation, you should make note of a change that I've just made. Now, your scan_expr is responsible for implementing segmentation. The scan routine will provide a bool flag `across_seg_boundary` to indicate whether the scan update is taking place across a segment boundary. The meaning of the two arguments `a` and `b` has also been clarified: `a` is an increment, and `b` is the value being incremented, potentially `across_seg_boundary`. To keep existing code working, simply wrap your scan expression in across_seg_boundary ? b : (original_scan_expr) Since this is all still unreleased code, there are no facilities in place to keep the old usage working. This became necessary in my use of this code, where I wanted to do a segmented scan on some part of the data and an unsegmented scan on another. This is now easily possible. This is all also documented here: http://documen.tician.de/pyopencl/array.html#making-custom-scan-kernels Sorry for the incompatible change. I'd also welcome feedback. Next, if you're writing scan code, this might come in handy: http://documen.tician.de/pyopencl/array.html#debugging-aids It's a completely sequential scan kernel generator/runner, best run on a CPU. It's meant to help isolate concurrency-related bugs from bugs in the code snippets passed to scan. Its interface is exactly the same as that of the parallel kernel generator/runner. Andreas

8 years, 8 months

Re: [PyOpenCL] Runtime error in Mountain Lion: symbol not found

by Bogdan Opanchuk

Hi Andreas, On Sun, Jul 29, 2012 at 6:25 AM, Andreas Kloeckner <lists(a)informa.tiker.net> wrote: > Argh. That function is part of the CL 1.2 spec. Apple seems to be > advertising 1.2 support, has that function in its CL headers, but > doesn't export it, it seems. Good job. :) > > Assuming what I just said is true, there's now a workaround for this in git. > Can you please try it out and report back? Yes, now it works fine. Thanks! > This is a bit mystifying. Where does that config option come from in > your case? Can you check your siteconf.py or ~/.aksetup-defaults.py? If > it's not coming from there, the default should pass the correct, unsplit > (i.e. with comma) version to distutils. You can check this by putting > > print conf["LDFLAGS"] > > into setup.py before the call to setup(). If the correct thing is passed > to distutils and it still comes out split, then that's a distutils > issue. Otherwise, please report back, and we'll investigate. It seems that the incorrect value is indeed coming from distutils. If I remove siteconf.py and just run "setup.py build", the flags are correct (and siteconf.py is not created).

8 years, 8 months

Runtime error in Mountain Lion: symbol not found

by Bogdan Opanchuk

Hi all, Has anyone tried to use PyOpenCL with OSX10.8? For me the compilation is successful, but I'm getting the following error: Python 2.7.3 (default, Jul 28 2012, 10:31:30) [GCC 4.2.1 Compatible Apple Clang 4.0 ((tags/Apple/clang-421.0.57))] on darwin Type "help", "copyright", "credits" or "license" for more information. >>> import pyopencl Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/Users/bogdan/.virtualenvs/py2/lib/python2.7/site-packages/pyopencl/__init__.py", line 4, in <module> import pyopencl._cl as _cl ImportError: dlopen(/Users/bogdan/.virtualenvs/py2/lib/python2.7/site-packages/pyopencl/_cl.so, 2): Symbol not found: _clCreateProgramWithBuiltInKernels Referenced from: /Users/bogdan/.virtualenvs/py2/lib/python2.7/site-packages/pyopencl/_cl.so Expected in: flat namespace in /Users/bogdan/.virtualenvs/py2/lib/python2.7/site-packages/pyopencl/_cl.so OpenCL framework seems to be connected to the _cl.so: $ otool -L /Users/bogdan/.virtualenvs/py2/lib/python2.7/site-packages/pyopencl/_cl.so /Users/bogdan/.virtualenvs/py2/lib/python2.7/site-packages/pyopencl/_cl.so: /System/Library/Frameworks/OpenCL.framework/Versions/A/OpenCL (compatibility version 1.0.0, current version 1.0.0) /usr/lib/libstdc++.6.dylib (compatibility version 7.0.0, current version 56.0.0) /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 169.3.0) There is also a minor issue during the compilation: clang does not quite understand the sequence "-Wl -framework OpenCL", and treats "-Wl" as if it were a warning-related option. This can be fixed by replacing '-Wl', '-framework', 'OpenCL' by '-Wl,-framework,OpenCL' in siteconf.py (or, better, somewhere in setup.py), but it does not help with the symbol problem.

8 years, 8 months

Scan

by Andreas Kloeckner

Hi all, I'm happy to announce that PyOpenCL git finally has a (more) competent scan implementation. Documentation here: http://documen.tician.de/pyopencl/array.html#module-pyopencl.scan Here are some feature bullets for your enjoyment: - Segmented scan - Look-behind on input (allows comparisons) - Look-behind on output (allows exclusive scan, stream compaction) - Allows transformed scan (aka map-scan) - Arbitrary argument signatures/many input/output arrays - Customizable via code snippets The following operations are already implemented: - copy_if (i.e. filter/stream compaction) - remove_if (i.e. filter/stream compaction) - partition - unique Each only took a couple of lines to implement using the generic scan kernel. If you've got feedback (especially before this goes into a release), I'd be happy to hear it. I'm planning to release this as part of 2012.2, soon. Andreas

8 years, 8 months

Re: [PyOpenCL] [PyCUDA] GPU algorithms library

by Bogdan Opanchuk

Hi Frédéric, On Thu, Jul 19, 2012 at 8:58 AM, Frédéric Bastien <nouiz(a)nouiz.org> wrote: > How much useful it is to abstract between PyCUDA > and PyOpenCL? Personnaly, I probably won't use that part, but I want > to abstract between CUDA and OpenCL. It was either that or to write almost identical libraries for PyCuda and PyOpenCL. The user is by no means forced to use cluda context, it is just a wrapper around PyCuda/PyOpenCL context that is passed to computation classes. After that corresponding array classes and synchronization functions from the target APIs can be used. But I personally use this abstraction because I get better GPU performance with CUDA, but I also need my programs to run on CPU with reasonable speed (mostly, for debugging), and wor that OpenCL is preferable. > I like the idea of making code generator that do transformation on the > input before doing other computation. This is something I wanted > Theano code generator to do, but I never got time to implement it. > What the current parameter derive_s_from_lp and derive_lp_from_s mean? These are two functions that are used to derive types. "s_from_lp" means "stores from loads and parameters" (transformations can also have scalar parameters, currently it can be seen in test_matrixmul.py:test_preprocessing). In the example the transformation is connected to "input pipeline", i.e. to the input parameter "A". So it takes some values from new external input parameters "A_re" and "A_im" (load=2) and combines them into "A" (store=1). The derivation functions work in the following situations: 1) When the object needs to derive types for the external signature from its basis parameters, derive_lp_from_s() is called and supplied with the type for "A", and expected to return types for "A_re" and "A_im" (also for parameters, but there are none, so the empty list is returned). 2) When the object needs to derive basis parameters from the arrays supplied to prepare_for(), derive_s_from_lp() is called which performs derivation in the other direction, producing data type for "A" from data types of "A_re" and "A_im". There are, in fact, four types of derivation functions. If we had a transformation connected to the "output pipeline", we would need derive_l_from_sp() and derive_sp_from_l(). Now that I think about it, "load" and "store" should probably be called "input" and "output", it is less ambiguous :) > Also the code section is not something I call readable... Is is only > because I never used Mako? Andreas, I think you used mako, do you find > this redable? These are only one-liners, so, yes, they seem fine to me. Perhaps, they would be more readable if I did not try to save on spacing, and used some temporary variables? Also, do you find kernels (dummy.mako and matrixmul.mako) hard to read too? > I'm not sure that forcing people to use Mako is a good idea. Can we do > without it? The amount of Mako in the transformations can be reduced if I use macros, for example, "LOAD1" instead of "${load.l1}". The latter was chosen because I planned to add some error checking, which would be less comprehensible with macros. It is much harder to avoid Mako for non-trivial tasks though, like getting corresponding complex data type for the real one, or providing support for multiplication of all combinations of complex/real numbers. Is it really such an issue? It is just Python code in curly braces, after all. > I still think that we need to provide the user not just with a common > gpu nd array object. We need to also provide fonctions on it. But I'm > not sure how we should do this. My project does not intersect with "general ndarray" idea at all. If there was some general array class instead of cl.Array/GPUArray, things would only make things easier for me. I just think that numpy way of providing functions for arrays is not that good in GPU case, as the overhead here is more significant, and should be made explicit and manageable for the user.

8 years, 8 months

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PyOpenCL July 2012