Happy about that! May I ask you to post the results here. I am curious since I never actually compared timings (and only blindly trusted Martin).
Thanks, Peter On Saturday, 22 October 2022 at 16:46:16 UTC+2 Simon wrote: > Yes, the issue is resolved and the computation time decreased > significantly. > > Thank you all! > > -Simon > > Am Sa., 22. Okt. 2022 um 12:57 Uhr schrieb Peter Munch < > peterr...@gmail.com>: > >> You are right. Release 9.3 uses the slow path for MappingQ. The reason is >> that here >> https://github.com/dealii/dealii/blob/ccfaddc2bab172d9d139dabc044d028f65bb480a/include/deal.II/matrix_free/fe_point_evaluation.h#L708-L711 >> >> we check for MappingQGeneric. At that time MappingQ and MappingQGeneric >> were different classes. In the meantime, we have merged the classes so that >> in release 9.4 and on master this is not an issue anymore. Is there a >> chance that you update deal.II. Alternatively, you could use >> MappingQGeneric instead of MappingQ. >> >> Hope this resolves this issue! >> >> Peter >> >> On Friday, 21 October 2022 at 10:59:35 UTC+2 Simon wrote: >> >>> I revised the appendix from my last message a little bit and attache now >>> a minimal working example (just 140 lines) along with a CMakeLists.txt. >>> After checking the profiling results from valgrind, the combination of >>> MappingQ with FE_Q takes *not* the fast path. >>> >>> For info: I use dealii version 9.3.2 >>> >>> Best, >>> Simon >>> >>> Am Do., 20. Okt. 2022 um 18:11 Uhr schrieb Simon Wiesheier < >>> simon.w...@gmail.com>: >>> >>>> " When you use FEPointEvaluation, you should construct it only once and >>>> re-use the same object for different points. Furthermore, you should also >>>> avoid to create "p_dofs" and the "std::vector" near the I was not clear >>>> with my original message. Anyway, the problem is the FEValues object that >>>> gets used. I am confused by your other message that you use FE_Q together >>>> with MappingQ - that combination should be supported and if it is not, we >>>> should take a look at a (reduced) code from you. " >>>> >>>> I added a snippet of my code (see appendix) in which I describe the >>>> logic as to what I am doing with FEPointEvaluation. >>>> In fact, constructing FEPointEvaluation (and the vector p_dofs) once >>>> and re-using them brings only minor changes as the overall costs are >>>> dominated by the call to reinit(). >>>> But, of course, it helps at least. >>>> >>>> I am surprised too that the fast path is not used. Maybe you can >>>> identify a problem in my code. >>>> Thank you! >>>> >>>> Best, >>>> Simon >>>> >>>> Am Do., 20. Okt. 2022 um 17:02 Uhr schrieb Martin Kronbichler < >>>> kronbichl...@gmail.com>: >>>> >>>>> Dear Simon, >>>>> >>>>> When you use FEPointEvaluation, you should construct it only once and >>>>> re-use the same object for different points. Furthermore, you should also >>>>> avoid to create "p_dofs" and the "std::vector" near the I was not clear >>>>> with my original message. Anyway, the problem is the FEValues object that >>>>> gets used. I am confused by your other message that you use FE_Q together >>>>> with MappingQ - that combination should be supported and if it is not, we >>>>> should take a look at a (reduced) code from you. >>>>> >>>>> Regarding the high timings: There is some parallelization by tasks >>>>> that gets done inside the constructor of FEValues. This has good intents >>>>> for the case that we are in 3D and have a reasonable amount of work to >>>>> do. >>>>> However, you are in 1D (if I read your code correctly), and then it is >>>>> having adverse effects. The reason is that the constructor of FEValues is >>>>> very likely completely dominated by memory allocation. When we have 1 >>>>> thread, everything is fine, but when we have multiple threads working >>>>> they >>>>> will start to interfere with each other when the request memory through >>>>> malloc(), which has to be coordinated by the operating system (and thus >>>>> gets slower). In fact, the big gap between compute time and wall time >>>>> shows >>>>> that there is a lot of time wasted by "system time" that does not do >>>>> actual >>>>> work on the cores. >>>>> >>>>> I guess the library could have a better measure of when to spawn tasks >>>>> in FEValues in similar context, but it is a lot of work to get this >>>>> right. >>>>> (This is why I keep avoiding it in critical functions.) >>>>> >>>>> Best, >>>>> Martin >>>>> >>>>> >>>>> On 20.10.22 16:47, Simon Wiesheier wrote: >>>>> >>>>> Update: >>>>> >>>>> I profiled my program with valgrind --tool=callgrind and could figure >>>>> out that >>>>> FEPointEvaluation creates an FEValues object along with a quadrature >>>>> object under the hood. >>>>> Closer inspection revealed that all constructors, destructors,... >>>>> associated with FEPointEvaluation >>>>> need roughly 5000 instructions more (per call!). >>>>> That said, FEValues is indeed the faster approach, at least for FE_Q >>>>> elements. >>>>> >>>>> export DEAL_II_NUM_THREADS=1 >>>>> eliminated the gap between cpu and wall time. >>>>> Using FEValues directly, I get cpu time 19.8 seconds >>>>> and in the case of FEPointEvaluation cpu time = 21.9 seconds; >>>>> Wall times are in the same ballpark. >>>>> Out of curiosity, why produces multi-threading such high wall times >>>>> (200 seconds) in my case?. >>>>> >>>>> These times are far too big given that the solution of the linear >>>>> system takes only about 13 seconds. >>>>> But based on what all of you have said, there is probably no other to >>>>> way to implement my problem. >>>>> >>>>> Best >>>>> Simon >>>>> >>>>> Am Do., 20. Okt. 2022 um 11:55 Uhr schrieb Simon Wiesheier < >>>>> simon.w...@gmail.com>: >>>>> >>>>>> Dear Martin and Wolfgang, >>>>>> >>>>>> " You seem to be looking for FEPointEvaluation. That class is shown >>>>>> in step-19 and provides, for simple FiniteElement types, a much faster >>>>>> way >>>>>> to evaluate solutions at arbitrary points within a cell. Do you want to >>>>>> give it a try? " >>>>>> >>>>>> I implemented the FEPointEvaluation approach like this: >>>>>> >>>>>> FEPointEvaluation<1,1> fe_eval(mapping, >>>>>> FE_Q<1>(1), >>>>>> update_gradients | >>>>>> update_values); >>>>>> fe_eval.reinit(cell, >>>>>> make_array_view(std::vector<Point<1>>{ref_point_energy_vol})); >>>>>> Vector<double> p_dofs(2); >>>>>> cell->get_dof_values(solution_global, p_dofs); >>>>>> fe_eval.evaluate(make_array_view(p_dofs), >>>>>> EvaluationFlags::values | >>>>>> EvaluationFlags::gradients); >>>>>> double val = fe_eval.get_value(0); >>>>>> Tensor<1,1> grad = fe_eval.get_gradient(0); >>>>>> >>>>>> I am using FE_Q elements of degree one and a MappingQ object also of >>>>>> degree one. >>>>>> >>>>>> Frankly, I do not really understand the measured computation times. >>>>>> My program has several loadsteps with nested Newton iterations: >>>>>> Loadstep 1: >>>>>> Assembly 1: cpu time 12.8 sec wall time 268.7 sec >>>>>> Assembly 2: cpu time 17.7 sec wall time 275.2 sec >>>>>> Assembly 3: cpu time 22.3 sec wall time 272.6 sec >>>>>> Assembly 4: cpu time 23.8 sec wall time 271.3sec >>>>>> Loadstep 2: >>>>>> Assembly 1: cpu time 14.3 sec wall time 260.0 sec >>>>>> Assembly 2: cpu time 16.9 sec wall time 262.1 sec >>>>>> Assembly 3: cpu time 18.5 sec wall time 270.6 sec >>>>>> Assembly 4: cpu time 17.1 sec wall time 262.2 sec >>>>>> ... >>>>>> >>>>>> Using FEValues instead of FEPointEvaluation, the results are: >>>>>> Loadstep 1: >>>>>> Assembly 1: cpu time 23.9 sec wall time 171.0 sec >>>>>> Assembly 2: cpu time 32.5 sec wall time 168.9 sec >>>>>> Assembly 3: cpu time 33.2 sec wall time 168.0 sec >>>>>> Assembly 4: cpu time 32.7 sec wall time 166.9 sec >>>>>> Loadstep 2: >>>>>> Assembly 1: cpu time 24.9 sec wall time 168.0 sec >>>>>> Assembly 2: cpu time 34.7 sec wall time 167.3 sec >>>>>> Assembly 3: cpu time 33.9 sec wall time 167.8 sec >>>>>> Assembly 4: cpu time 34.3 sec wall time 167.7 sec >>>>>> ... >>>>>> >>>>>> Clearly, the fluctuations using FEValues are smaller than in case of >>>>>> FEPointEvaluation. >>>>>> Anyway, using FEPointEvaluation the cpu time is smaller but the wall >>>>>> time substantially bigger. >>>>>> If I am not mistaken, the values cpu time 34.3 sec and wall time >>>>>> 167.7 sec mean that >>>>>> the cpu needs 34.3 sec to execute my assembly routine and has to wait >>>>>> in the >>>>>> remaining 167.7-34.3 seconds. >>>>>> This huge gap between cpu and wall time has to be related to what I >>>>>> do with FEValues or FEPointEvaluation >>>>>> as cpu and wall time are nearly balanced if I use either neither of >>>>>> them. >>>>>> What might be the problem? >>>>>> >>>>>> Best >>>>>> Simon >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> >>>>>> Am Mi., 19. Okt. 2022 um 22:34 Uhr schrieb Wolfgang Bangerth < >>>>>> bang...@colostate.edu>: >>>>>> >>>>>>> On 10/19/22 08:45, Simon Wiesheier wrote: >>>>>>> > >>>>>>> > What I want to do boils down to the following: >>>>>>> > Given the reference co-ordinates of a point 'p', along with the >>>>>>> cell on >>>>>>> > which 'p' lives, >>>>>>> > give me the value and gradient of a finite element function >>>>>>> evaluated at >>>>>>> > 'p'. >>>>>>> > >>>>>>> > My idea was to create a quadrature object with 'p' being the only >>>>>>> > quadrature point and pass this >>>>>>> > quadrature object to the FEValues object and finally do the >>>>>>> > .reinit(cell) call (then, of course, get_function_values()...) >>>>>>> > 'p' is different for all (2.5 million) quadrature points, which is >>>>>>> why I >>>>>>> > create the FEValues object so many times. >>>>>>> >>>>>>> It's worth pointing out that is exactly what >>>>>>> VectorTools::point_values() >>>>>>> does. >>>>>>> >>>>>>> (As others have already mentioned, if you want to do that many many >>>>>>> times over, this is too expensive and you should be using >>>>>>> FEPointEvaluation instead.) >>>>>>> >>>>>>> Best >>>>>>> W. >>>>>>> >>>>>>> -- >>>>>>> >>>>>>> ------------------------------------------------------------------------ >>>>>>> Wolfgang Bangerth email: >>>>>>> bang...@colostate.edu >>>>>>> www: >>>>>>> http://www.math.colostate.edu/~bangerth/ >>>>>>> >>>>>>> -- >>>>>>> The deal.II project is located at http://www.dealii.org/ >>>>>>> For mailing list/forum options, see >>>>>>> https://groups.google.com/d/forum/dealii?hl=en >>>>>>> --- >>>>>>> You received this message because you are subscribed to the Google >>>>>>> Groups "deal.II User Group" group. >>>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>>> send an email to dealii+un...@googlegroups.com. >>>>>>> To view this discussion on the web visit >>>>>>> https://groups.google.com/d/msgid/dealii/cd1c8fa0-443d-b7bf-b433-f5ab033a247c%40colostate.edu >>>>>>> . >>>>>>> >>>>>> -- >>>>> The deal.II project is located at http://www.dealii.org/ >>>>> For mailing list/forum options, see >>>>> https://groups.google.com/d/forum/dealii?hl=en >>>>> --- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "deal.II User Group" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to dealii+un...@googlegroups.com. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/dealii/CAM50jEt3LjNS%2BF%3D2pGUSHRNbaHy9EzRfogpyBxb51-7M%3DALxrA%40mail.gmail.com >>>>> >>>>> <https://groups.google.com/d/msgid/dealii/CAM50jEt3LjNS%2BF%3D2pGUSHRNbaHy9EzRfogpyBxb51-7M%3DALxrA%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>>> -- >>>>> The deal.II project is located at http://www.dealii.org/ >>>>> For mailing list/forum options, see >>>>> https://groups.google.com/d/forum/dealii?hl=en >>>>> --- >>>>> You received this message because you are subscribed to a topic in the >>>>> Google Groups "deal.II User Group" group. >>>>> To unsubscribe from this topic, visit >>>>> https://groups.google.com/d/topic/dealii/uAplhH99yg4/unsubscribe. >>>>> To unsubscribe from this group and all its topics, send an email to >>>>> dealii+un...@googlegroups.com. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/dealii/24ba8ef3-39f4-af6c-7296-02677827d6d3%40gmail.com >>>>> >>>>> <https://groups.google.com/d/msgid/dealii/24ba8ef3-39f4-af6c-7296-02677827d6d3%40gmail.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> -- >> The deal.II project is located at http://www.dealii.org/ >> For mailing list/forum options, see >> https://groups.google.com/d/forum/dealii?hl=en >> --- >> You received this message because you are subscribed to the Google Groups >> "deal.II User Group" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to dealii+un...@googlegroups.com. >> > To view this discussion on the web visit >> https://groups.google.com/d/msgid/dealii/b9e2b386-f9f1-4046-9d35-cfbf045beb4bn%40googlegroups.com >> >> <https://groups.google.com/d/msgid/dealii/b9e2b386-f9f1-4046-9d35-cfbf045beb4bn%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- The deal.II project is located at http://www.dealii.org/ For mailing list/forum options, see https://groups.google.com/d/forum/dealii?hl=en --- You received this message because you are subscribed to the Google Groups "deal.II User Group" group. To unsubscribe from this group and stop receiving emails from it, send an email to dealii+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/dealii/725f9507-0236-47f7-b0df-03c7d21fe503n%40googlegroups.com.