Hi Andreas, - good news: I made good progress on introducing a generic context. For code lines such as viennacl::vector<T> x = y + z; the vector x is created in the correct context (i.e. deduced from y, z). This resolves most of the issues with temporaries.
- bad news: I haven't found enough time for applying the same scheme to matrices yet. As the infrastructure is mostly ready, this shouldn't take too long and be completed during tomorrow. Stay tuned :-) Best regards, Karli On 07/21/2013 09:59 AM, Andreas IHU wrote: > Hi again, > > here's another problem which just occured to me while working with the latest > developer version from GitHub. > > I have a program which has to iteratively solve a number of independent > equation systems. > The actual number of systems may vary between 1 and 10. > Because they are totally independent from each other, we assign each system a > number of OpenMP threads allowing them to be solved in parallel at the same > time. > > Now I tried to integrate ViennaCL into that scheme and used the > multithreaded.cpp example as a guide. > The main difference is that I use OpenMP threads instead of Boost ones. > > My approach is to first create as many different OpenCL contexts as equation > systems do exist and split the existing OpenCL devices over them. > If just one device exists, its gonna be used by all contexts, which shouldn't > be a problem. > Then I call > > viennacl::ocl::switch_context() > > for every equation system and allocate all the required VCL vectors and > matrices required just afterwards. > This makes sure they are assigned and allocated for the context they actually > belong to. > This all still takes place in serial mode and doesn't bring me in trouble :-) > > The actual problems begin, when the solver routine of our programm is called > in parallel mode. > > 1.) It fills a preallocated STL matrix with the current coefficients and > updates the RHS vector. > These are gonna be copied to their VCL counterparts using > viennacl::copy(stlmat,vclmat); > What happens exactly during this call is that > > viennacl::copy()-> > viennacl::detail::copy_impl()-> > gpu_matrix.set()-> > viennacl::backend::memory_create() (in > compressed_matrix.hpp at row 519ff) > > allocates 3 new buffers which should be created for the context they > belong to. > This could be achieved by calling > viennacl::ocl::switch_context() > before the copy takes place. > Unfortunately this isn't an option because I would have to use a OMP > Critical region to make sure that the parallel calls to switch_context() & > copy() do not overlap each other leading to race conditions. > So what I need is an oportunity to specify a context in which the copy() > takes place without having to change the actual context. > > 2.) The same problem happens afterwards when calling the actual > Preconditioner and solve() routines. > They too allocate memory for the currently active context. > > I built a temporary workaround by putting the whole sequence into a OpenMP > Critical region which prevents context errors in ViennaCL, > but makes it impossible to solve the equation systems in parallel. > > Any suggestions on that? > Kind regards > Andreas Rost > > > > > ------------------------------------------------------------------------------ > See everything from the browser to the database with AppDynamics > Get end-to-end visibility with application monitoring from AppDynamics > Isolate bottlenecks and diagnose root cause in seconds. > Start your free trial of AppDynamics Pro today! > http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk > _______________________________________________ > ViennaCL-devel mailing list > ViennaCL-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/viennacl-devel > ------------------------------------------------------------------------------ See everything from the browser to the database with AppDynamics Get end-to-end visibility with application monitoring from AppDynamics Isolate bottlenecks and diagnose root cause in seconds. Start your free trial of AppDynamics Pro today! http://pubads.g.doubleclick.net/gampad/clk?id=48808831&iu=/4140/ostg.clktrk _______________________________________________ ViennaCL-devel mailing list ViennaCL-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viennacl-devel
