> On 20 Dec 2023, at 8:42 AM, Sreeram R Venkat <[email protected]> wrote: > > Ok, I think the error I'm getting has something to do with how the multiple > solves are being done in succession. I'll try to see if there's anything I'm > doing wrong there. > > One question about the -pc_type lu -ksp_type preonly method: do you know > which parts of the solve (factorization/triangular solves) are done on host > and which are done on device?
I think only the triangular solves can be done on device. Since you have many right-hand sides, it may not be that bad. GPU people will hopefully give you a more insightful answer. Thanks, Pierre > Thanks, > Sreeram > > On Sat, Dec 16, 2023 at 10:56 PM Pierre Jolivet <[email protected] > <mailto:[email protected]>> wrote: >> Unfortunately, I am not able to reproduce such a failure with your input >> matrix. >> I’ve used ex79 that I linked previously and the system is properly solved. >> $ ./ex79 -pc_type hypre -ksp_type hpddm -ksp_hpddm_type cg >> -ksp_converged_reason -ksp_view_mat ascii::ascii_info -ksp_view_rhs >> ascii::ascii_info >> Linear solve converged due to CONVERGED_RTOL iterations 6 >> Mat Object: 1 MPI process >> type: seqaijcusparse >> rows=289, cols=289 >> total: nonzeros=2401, allocated nonzeros=2401 >> total number of mallocs used during MatSetValues calls=0 >> not using I-node routines >> Mat Object: 1 MPI process >> type: seqdensecuda >> rows=289, cols=10 >> total: nonzeros=2890, allocated nonzeros=2890 >> total number of mallocs used during MatSetValues calls=0 >> >> You mentioned in a subsequent email that you are interested in systems with >> at most 1E6 unknowns, and up to 1E4 right-hand sides. >> I’m not sure you can expect significant gains from using GPU for such >> systems. >> Probably, the fastest approach would indeed be -pc_type lu -ksp_type preonly >> -ksp_matsolve_batch_size 100 or something, depending on the memory available >> on your host. >> >> Thanks, >> Pierre >> >>> On 15 Dec 2023, at 9:52 PM, Sreeram R Venkat <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Here are the ksp_view files. I set the options -ksp_error_if_not_converged >>> to try to get the vectors that caused the error. I noticed that some of the >>> KSPMatSolves converge while others don't. In the code, the solves are >>> called as: >>> >>> input vector v --> insert data of v into a dense mat --> KSPMatSolve() --> >>> MatMatMult() --> KSPMatSolve() --> insert data of dense mat into output >>> vector w -- output w >>> >>> The operator used in the KSP is a Laplacian-like operator, and the >>> MatMatMult is with a Mass Matrix. The whole thing is supposed to be a solve >>> with a biharmonic-like operator. I can also run it with only the first >>> KSPMatSolve (i.e. just a Laplacian-like operator). In that case, the KSP >>> reportedly converges after 0 iterations (see the next line), but this >>> causes problems in other parts of the code later on. >>> >>> I saw that sometimes the first KSPMatSolve "converges" after 0 iterations >>> due to CONVERGED_RTOL. Then, the second KSPMatSolve produces a NaN/Inf. I >>> tried setting ksp_min_it, but that didn't seem to do anything. >>> >>> I'll keep trying different options and also try to get the MWE made (this >>> KSPMatSolve is pretty performance critical for us). >>> >>> Thanks for all your help, >>> Sreeram >>> >>> On Fri, Dec 15, 2023 at 1:01 AM Pierre Jolivet <[email protected] >>> <mailto:[email protected]>> wrote: >>>> >>>>> On 14 Dec 2023, at 11:45 PM, Sreeram R Venkat <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> >>>>> Thanks, I will try to create a minimal reproducible example. This may >>>>> take me some time though, as I need to figure out how to extract only the >>>>> relevant parts (the full program this solve is used in is getting quite >>>>> complex). >>>> >>>> You could just do -ksp_view_mat binary:Amat.bin -ksp_view_pmat >>>> binary:Pmat.bin -ksp_view_rhs binary:rhs.bin and send me those three files >>>> (I’m guessing your are using double-precision scalars with 32-bit >>>> PetscInt). >>>> >>>>> I'll also try out some of the BoomerAMG options to see if that helps. >>>> >>>> These should work (this is where all “PCMatApply()-ready” PC are being >>>> tested): >>>> https://petsc.org/release/src/ksp/ksp/tutorials/ex79.c.html#line215 >>>> You can see it’s also testing PCHYPRE + KSPHPDDM on device (but not with >>>> HIP). >>>> I’m aware the performance should not be optimal (see your comment about >>>> host/device copies), I’ve money to hire someone to work on this but: a) I >>>> need to find the correct engineer/post-doc, b) I currently don’t have good >>>> use cases (of course, I could generate a synthetic benchmark, for science). >>>> So even if you send me the three Mat, a MWE would be appreciated if the >>>> KSPMatSolve() is performance-critical for you (see point b) from above). >>>> >>>> Thanks, >>>> Pierre >>>> >>>>> Thanks, >>>>> Sreeram >>>>> >>>>> On Thu, Dec 14, 2023, 1:12 PM Pierre Jolivet <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>>> >>>>>> >>>>>>> On 14 Dec 2023, at 8:02 PM, Sreeram R Venkat <[email protected] >>>>>>> <mailto:[email protected]>> wrote: >>>>>>> >>>>>>> Hello Pierre, >>>>>>> >>>>>>> Thank you for your reply. I tried out the HPDDM CG as you said, and it >>>>>>> seems to be doing the batched solves, but the KSP is not converging due >>>>>>> to a NaN or Inf being generated. I also noticed there are a lot of >>>>>>> host-to-device and device-to-host copies of the matrices (the >>>>>>> non-batched KSP solve did not have any memcopies). I have attached >>>>>>> dump.0 again. Could you please take a look? >>>>>> >>>>>> Yes, but you’d need to send me something I can run with your set of >>>>>> options (if you are more confident doing this in private, you can remove >>>>>> the list from c/c). >>>>>> Not all BoomerAMG smoothers handle blocks of right-hand sides, and there >>>>>> is not much error checking, so instead of erroring out, this may be the >>>>>> reason why you are getting garbage. >>>>>> >>>>>> Thanks, >>>>>> Pierre >>>>>> >>>>>>> Thanks, >>>>>>> Sreeram >>>>>>> >>>>>>> On Thu, Dec 14, 2023 at 12:42 AM Pierre Jolivet <[email protected] >>>>>>> <mailto:[email protected]>> wrote: >>>>>>>> Hello Sreeram, >>>>>>>> KSPCG (PETSc implementation of CG) does not handle solves with >>>>>>>> multiple columns at once. >>>>>>>> There is only a single native PETSc KSP implementation which handles >>>>>>>> solves with multiple columns at once: KSPPREONLY. >>>>>>>> If you use --download-hpddm, you can use a CG (or GMRES, or more >>>>>>>> advanced methods) implementation which handles solves with multiple >>>>>>>> columns at once (via -ksp_type hpddm -ksp_hpddm_type cg or >>>>>>>> KSPSetType(ksp, KSPHPDDM); KSPHPDDMSetType(ksp, KSP_HPDDM_TYPE_CG);). >>>>>>>> I’m the main author of HPDDM, there is preliminary support for device >>>>>>>> matrices, but if it’s not working as intended/not faster than column >>>>>>>> by column, I’d be happy to have a deeper look (maybe in private), >>>>>>>> because most (if not all) of my users interested in (pseudo-)block >>>>>>>> Krylov solvers (i.e., solvers that treat right-hand sides in a single >>>>>>>> go) are using plain host matrices. >>>>>>>> >>>>>>>> Thanks, >>>>>>>> Pierre >>>>>>>> >>>>>>>> PS: you could have a look at >>>>>>>> https://www.sciencedirect.com/science/article/abs/pii/S0898122121000055 >>>>>>>> to understand the philosophy behind block iterative methods in PETSc >>>>>>>> (and in HPDDM), src/mat/tests/ex237.c, the benchmark I mentioned >>>>>>>> earlier, was developed in the context of this paper to produce Figures >>>>>>>> 2-3. Note that this paper is now slightly outdated, since then, >>>>>>>> PCHYPRE and PCMG (among others) have been made “PCMatApply()-ready”. >>>>>>>> >>>>>>>>> On 13 Dec 2023, at 11:05 PM, Sreeram R Venkat <[email protected] >>>>>>>>> <mailto:[email protected]>> wrote: >>>>>>>>> >>>>>>>>> Hello Pierre, >>>>>>>>> >>>>>>>>> I am trying out the KSPMatSolve with the BoomerAMG preconditioner. >>>>>>>>> However, I am noticing that it is still solving column by column >>>>>>>>> (this is stated explicitly in the info dump attached). I looked at >>>>>>>>> the code for KSPMatSolve_Private() and saw that as long as >>>>>>>>> ksp->ops->matsolve is true, it should do the batched solve, though >>>>>>>>> I'm not sure where that gets set. >>>>>>>>> >>>>>>>>> I am using the options -pc_type hypre -pc_hypre_type boomeramg when >>>>>>>>> running the code. >>>>>>>>> >>>>>>>>> Can you please help me with this? >>>>>>>>> >>>>>>>>> Thanks, >>>>>>>>> Sreeram >>>>>>>>> >>>>>>>>> >>>>>>>>> On Thu, Dec 7, 2023 at 4:04 PM Mark Adams <[email protected] >>>>>>>>> <mailto:[email protected]>> wrote: >>>>>>>>>> N.B., AMGX interface is a bit experimental. >>>>>>>>>> Mark >>>>>>>>>> >>>>>>>>>> On Thu, Dec 7, 2023 at 4:11 PM Sreeram R Venkat <[email protected] >>>>>>>>>> <mailto:[email protected]>> wrote: >>>>>>>>>>> Oh, in that case I will try out BoomerAMG. Getting AMGX to build >>>>>>>>>>> correctly was also tricky so hopefully the HYPRE build will be >>>>>>>>>>> easier. >>>>>>>>>>> >>>>>>>>>>> Thanks, >>>>>>>>>>> Sreeram >>>>>>>>>>> >>>>>>>>>>> On Thu, Dec 7, 2023, 3:03 PM Pierre Jolivet <[email protected] >>>>>>>>>>> <mailto:[email protected]>> wrote: >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>>> On 7 Dec 2023, at 9:37 PM, Sreeram R Venkat <[email protected] >>>>>>>>>>>>> <mailto:[email protected]>> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> Thank you Barry and Pierre; I will proceed with the first option. >>>>>>>>>>>>> >>>>>>>>>>>>> I want to use the AMGX preconditioner for the KSP. I will try it >>>>>>>>>>>>> out and see how it performs. >>>>>>>>>>>> >>>>>>>>>>>> Just FYI, AMGX does not handle systems with multiple RHS, and thus >>>>>>>>>>>> has no PCMatApply() implementation. >>>>>>>>>>>> BoomerAMG does, and there is a PCMatApply_HYPRE_BoomerAMG() >>>>>>>>>>>> implementation. >>>>>>>>>>>> But let us know if you need assistance figuring things out. >>>>>>>>>>>> >>>>>>>>>>>> Thanks, >>>>>>>>>>>> Pierre >>>>>>>>>>>> >>>>>>>>>>>>> Thanks, >>>>>>>>>>>>> Sreeram >>>>>>>>>>>>> >>>>>>>>>>>>> On Thu, Dec 7, 2023 at 2:02 PM Pierre Jolivet <[email protected] >>>>>>>>>>>>> <mailto:[email protected]>> wrote: >>>>>>>>>>>>>> To expand on Barry’s answer, we have observed repeatedly that >>>>>>>>>>>>>> MatMatMult with MatAIJ performs better than MatMult with >>>>>>>>>>>>>> MatMAIJ, you can reproduce this on your own with >>>>>>>>>>>>>> https://petsc.org/release/src/mat/tests/ex237.c.html. >>>>>>>>>>>>>> Also, I’m guessing you are using some sort of preconditioner >>>>>>>>>>>>>> within your KSP. >>>>>>>>>>>>>> Not all are “KSPMatSolve-ready”, i.e., they may treat blocks of >>>>>>>>>>>>>> right-hand sides column by column, which is very inefficient. >>>>>>>>>>>>>> You could run your code with -info dump and send us dump.0 to >>>>>>>>>>>>>> see what needs to be done on our end to make things more >>>>>>>>>>>>>> efficient, should you not be satisfied with the current >>>>>>>>>>>>>> performance of the code. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Thanks, >>>>>>>>>>>>>> Pierre >>>>>>>>>>>>>> >>>>>>>>>>>>>>> On 7 Dec 2023, at 8:34 PM, Barry Smith <[email protected] >>>>>>>>>>>>>>> <mailto:[email protected]>> wrote: >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> On Dec 7, 2023, at 1:17 PM, Sreeram R Venkat >>>>>>>>>>>>>>>> <[email protected] <mailto:[email protected]>> wrote: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> I have 2 sequential matrices M and R (both MATSEQAIJCUSPARSE >>>>>>>>>>>>>>>> of size n x n) and a vector v of size n*m. v = [v_1 , v_2 ,... >>>>>>>>>>>>>>>> , v_m] where v_i has size n. The data for v can be stored >>>>>>>>>>>>>>>> either in column-major or row-major order. Now, I want to do >>>>>>>>>>>>>>>> 2 types of operations: >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> 1. Matvecs of the form M*v_i = w_i, for i = 1..m. >>>>>>>>>>>>>>>> 2. KSPSolves of the form R*x_i = v_i, for i = 1..m. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> From what I have read on the documentation, I can think of 2 >>>>>>>>>>>>>>>> approaches. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> 1. Get the pointer to the data in v (column-major) and use it >>>>>>>>>>>>>>>> to create a dense matrix V. Then do a MatMatMult with M*V = W, >>>>>>>>>>>>>>>> and take the data pointer of W to create the vector w. For >>>>>>>>>>>>>>>> KSPSolves, use KSPMatSolve with R and V. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> 2. Create a MATMAIJ using M/R and use that for matvecs >>>>>>>>>>>>>>>> directly with the vector v. I don't know if KSPSolve with the >>>>>>>>>>>>>>>> MATMAIJ will know that it is a multiple RHS system and act >>>>>>>>>>>>>>>> accordingly. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Which would be the more efficient option? >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Use 1. >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> As a side-note, I am also wondering if there is a way to use >>>>>>>>>>>>>>>> row-major storage of the vector v. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> No >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> The reason is that this could allow for more coalesced memory >>>>>>>>>>>>>>>> access when doing matvecs. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> PETSc matrix-vector products use BLAS GMEV matrix-vector >>>>>>>>>>>>>>> products for the computation so in theory they should already >>>>>>>>>>>>>>> be well-optimized >>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> >>>>>>>>>>>>>>>> Thanks, >>>>>>>>>>>>>>>> Sreeram >>>>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>> <dump.0> >>>>>>>> >>>>>>> <dump.0> >>>>>> >>>> >>> <Pmat.bin><Amat.bin><rhs.bin> >>
