Is there a difference in memory usage on your tiny problem? I assume no. I don't see anything that could come from GAMG other than the RAP stuff that you have discussed already.
On Mon, Mar 11, 2019 at 9:32 AM Myriam Peyrounette < myriam.peyroune...@idris.fr> wrote: > The code I am using here is the example 42 of PETSc ( > https://www.mcs.anl.gov/petsc/petsc-3.9/src/ksp/ksp/examples/tutorials/ex42.c.html). > Indeed it solves the Stokes equation. I thought it was a good idea to use > an example you might know (and didn't find any that uses GAMG functions). I > just changed the PCMG setup so that the memory problem appears. And it > appears when adding PCGAMG. > > I don't care about the performance or even the result rightness here, but > only about the difference in memory use between 3.6 and 3.10. Do you think > finding a more adapted script would help? > > I used the threshold of 0.1 only once, at the beginning, to test its > influence. I used the default threshold (of 0, I guess) for all the other > runs. > > Myriam > > Le 03/11/19 à 13:52, Mark Adams a écrit : > > In looking at this larger scale run ... > > * Your eigen estimates are much lower than your tiny test problem. But > this is Stokes apparently and it should not work anyway. Maybe you have a > small time step that adds a lot of mass that brings the eigen estimates > down. And your min eigenvalue (not used) is positive. I would expect > negative for Stokes ... > > * You seem to be setting a threshold value of 0.1 -- that is very high > > * v3.6 says "using nonzero initial guess" but this is not in v3.10. Maybe > we just stopped printing that. > > * There were some changes to coasening parameters in going from v3.6 but > it does not look like your problem was effected. (The coarsening algo is > non-deterministic by default and you can see small difference on different > runs) > > * We may have also added a "noisy" RHS for eigen estimates by default from > v3.6. > > * And for non-symetric problems you can try -pc_gamg_agg_nsmooths 0, but > again GAMG is not built for Stokes anyway. > > > On Tue, Mar 5, 2019 at 11:53 AM Myriam Peyrounette < > myriam.peyroune...@idris.fr> wrote: > >> I used PCView to display the size of the linear system in each level of >> the MG. You'll find the outputs attached to this mail (zip file) for both >> the default threshold value and a value of 0.1, and for both 3.6 and 3.10 >> PETSc versions. >> >> For convenience, I summarized the information in a graph, also attached >> (png file). >> >> As you can see, there are slight differences between the two versions but >> none is critical, in my opinion. Do you see anything suspicious in the >> outputs? >> >> + I can't find the default threshold value. Do you know where I can find >> it? >> >> Thanks for the follow-up >> >> Myriam >> >> Le 03/05/19 à 14:06, Matthew Knepley a écrit : >> >> On Tue, Mar 5, 2019 at 7:14 AM Myriam Peyrounette < >> myriam.peyroune...@idris.fr> wrote: >> >>> Hi Matt, >>> >>> I plotted the memory scalings using different threshold values. The two >>> scalings are slightly translated (from -22 to -88 mB) but this gain is >>> neglectable. The 3.6-scaling keeps being robust while the 3.10-scaling >>> deteriorates. >>> >>> Do you have any other suggestion? >>> >> Mark, what is the option she can give to output all the GAMG data? >> >> Also, run using -ksp_view. GAMG will report all the sizes of its grids, >> so it should be easy to see >> if the coarse grid sizes are increasing, and also what the effect of the >> threshold value is. >> >> Thanks, >> >> Matt >> >>> Thanks >>> Myriam >>> >>> Le 03/02/19 à 02:27, Matthew Knepley a écrit : >>> >>> On Fri, Mar 1, 2019 at 10:53 AM Myriam Peyrounette via petsc-users < >>> petsc-users@mcs.anl.gov> wrote: >>> >>>> Hi, >>>> >>>> I used to run my code with PETSc 3.6. Since I upgraded the PETSc version >>>> to 3.10, this code has a bad memory scaling. >>>> >>>> To report this issue, I took the PETSc script ex42.c and slightly >>>> modified it so that the KSP and PC configurations are the same as in my >>>> code. In particular, I use a "personnalised" multi-grid method. The >>>> modifications are indicated by the keyword "TopBridge" in the attached >>>> scripts. >>>> >>>> To plot the memory (weak) scaling, I ran four calculations for each >>>> script with increasing problem sizes and computations cores: >>>> >>>> 1. 100,000 elts on 4 cores >>>> 2. 1 million elts on 40 cores >>>> 3. 10 millions elts on 400 cores >>>> 4. 100 millions elts on 4,000 cores >>>> >>>> The resulting graph is also attached. The scaling using PETSc 3.10 >>>> clearly deteriorates for large cases, while the one using PETSc 3.6 is >>>> robust. >>>> >>>> After a few tests, I found that the scaling is mostly sensitive to the >>>> use of the AMG method for the coarse grid (line 1780 in >>>> main_ex42_petsc36.cc). In particular, the performance strongly >>>> deteriorates when commenting lines 1777 to 1790 (in >>>> main_ex42_petsc36.cc). >>>> >>>> Do you have any idea of what changed between version 3.6 and version >>>> 3.10 that may imply such degradation? >>>> >>> >>> I believe the default values for PCGAMG changed between versions. It >>> sounds like the coarsening rate >>> is not great enough, so that these grids are too large. This can be set >>> using: >>> >>> >>> https://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/PC/PCGAMGSetThreshold.html >>> >>> There is some explanation of this effect on that page. Let us know if >>> setting this does not correct the situation. >>> >>> Thanks, >>> >>> Matt >>> >>> >>>> Let me know if you need further information. >>>> >>>> Best, >>>> >>>> Myriam Peyrounette >>>> >>>> >>>> -- >>>> Myriam Peyrounette >>>> CNRS/IDRIS - HLST >>>> -- >>>> >>>> >>> >>> -- >>> What most experimenters take for granted before they begin their >>> experiments is infinitely more interesting than any results to which their >>> experiments lead. >>> -- Norbert Wiener >>> >>> https://www.cse.buffalo.edu/~knepley/ >>> <http://www.cse.buffalo.edu/%7Eknepley/> >>> >>> >>> -- >>> Myriam Peyrounette >>> CNRS/IDRIS - HLST >>> -- >>> >>> >> >> -- >> What most experimenters take for granted before they begin their >> experiments is infinitely more interesting than any results to which their >> experiments lead. >> -- Norbert Wiener >> >> https://www.cse.buffalo.edu/~knepley/ >> <http://www.cse.buffalo.edu/%7Eknepley/> >> >> >> -- >> Myriam Peyrounette >> CNRS/IDRIS - HLST >> -- >> >> > -- > Myriam Peyrounette > CNRS/IDRIS - HLST > -- > >