Sorry, I was wrong. Of course, it is the other way round. The fast one is 3 times faster.
-Simon Am So., 23. Okt. 2022 um 10:37 Uhr schrieb Peter Munch < peterrmue...@gmail.com>: > Now, I am lost. The fast one is 3 times slower!? > > Peter > > On Sunday, 23 October 2022 at 10:33:38 UTC+2 Simon wrote: > >> Certainly. >> When using the slow path, i.e. MappingQ in version 9.3.2, the cpu time is >> about 6.3 seconds. >> In case of the fast path, i.e. MappingQGeneric in version 9.3.2, the cpu >> time is about 18.7 seconds. >> Crudely, the .reinit function associated with the FEPointEvaluation >> objects is called about 1.2 million times. >> >> Best, >> Simon >> >> Am Sa., 22. Okt. 2022 um 17:09 Uhr schrieb Peter Munch < >> peterr...@gmail.com>: >> >>> 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 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>>>>>>>> . >>>>>>>> >>>>>>>> -- >>>>>>>> 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, 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