On Sat, Jan 22, 2022 at 9:00 PM Junchao Zhang <junchao.zh...@gmail.com> wrote:
> > > > On Sat, Jan 22, 2022 at 5:00 PM Barry Smith <bsm...@petsc.dev> wrote: > >> >> The GPU flop rate (when 100 percent flops on the GPU) should always be >> higher than the overall flop rate (the previous column). For large problems >> they should be similar, for small problems the GPU one may be much higher. >> >> If the CPU one is higher (when 100 percent flops on the GPU) something >> must be wrong with the logging. I looked at the code for the two cases and >> didn't see anything obvious. >> >> Junchao and Jacob, >> I think some of the timing code in the Kokkos interface is wrong. >> >> * The PetscLogGpuTimeBegin/End should be inside the viewer access >> code not outside it. (The GPU time is an attempt to best time the kernels, >> not other processing around the use of the kernels, that other stuff is >> captured in the general LogEventBegin/End. >> > What about potential host to device memory copy before calling a kernel? Should we count it in the kernel time? Good point > >> * The use of WaitForKokkos() is confusing and seems inconsistent. >> > I need to have a look. Until now, I have not paid much attention to kokkos > profiling. > >> -For example it is used in VecTDot_SeqKokkos() which I would >> think has a barrier anyways because it puts a scalar result into update? >> -Plus PetscLogGpuTimeBegin/End is suppose to already have >> suitable system (that Hong added) to ensure the kernel is complete; reading >> the manual page and looking at Jacobs cupmcontext.hpp it seems to be there >> so I don't think WaitForKokkos() is needed in most places (or is Kokkos >> asynchronous and needs this for correctness?) >> But these won't explain the strange result of overall flop rate being >> higher than GPU flop rate. >> >> Barry >> >> >> >> >> >> On Jan 22, 2022, at 11:44 AM, Mark Adams <mfad...@lbl.gov> wrote: >> >> I am getting some funny timings and I'm trying to figure it out. >> I figure the gPU flop rates are bit higher because the timers are inside >> of the CPU timers, but *some are a lot bigger or inverted* >> >> --- Event Stage 2: KSP Solve only >> >> MatMult 400 1.0 1.0094e+01 1.2 1.07e+11 1.0 3.7e+05 6.1e+04 >> 0.0e+00 2 55 62 54 0 68 91100100 0 671849 857147 0 0.00e+00 0 >> 0.00e+00 100 >> MatView 2 1.0 4.5257e-03 2.5 0.00e+00 0.0 0.0e+00 0.0e+00 >> 2.0e+00 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00e+00 0 >> 0.00e+00 0 >> KSPSolve 2 1.0 1.4591e+01 1.1 1.18e+11 1.0 3.7e+05 6.1e+04 >> 1.2e+03 2 60 62 54 60 100100100100100 512399 804048 0 0.00e+00 0 >> 0.00e+00 100 >> SFPack 400 1.0 2.4545e-03 1.4 0.00e+00 0.0 0.0e+00 0.0e+00 >> 0.0e+00 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00e+00 0 >> 0.00e+00 0 >> SFUnpack 400 1.0 9.4637e-05 1.7 0.00e+00 0.0 0.0e+00 0.0e+00 >> 0.0e+00 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00e+00 0 >> 0.00e+00 0 >> VecTDot 802 1.0 3.0577e+00 2.1 3.36e+09 1.0 0.0e+00 0.0e+00 >> 8.0e+02 0 2 0 0 40 13 3 0 0 67 *69996 488328* 0 0.00e+00 >> 0 0.00e+00 100 >> VecNorm 402 1.0 1.9597e+00 3.4 1.69e+09 1.0 0.0e+00 0.0e+00 >> 4.0e+02 0 1 0 0 20 6 1 0 0 33 54744 571507 0 0.00e+00 0 >> 0.00e+00 100 >> VecCopy 4 1.0 1.7143e-0228.6 0.00e+00 0.0 0.0e+00 0.0e+00 >> 0.0e+00 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00e+00 0 >> 0.00e+00 0 >> VecSet 4 1.0 3.8051e-0316.9 0.00e+00 0.0 0.0e+00 0.0e+00 >> 0.0e+00 0 0 0 0 0 0 0 0 0 0 0 0 0 0.00e+00 0 >> 0.00e+00 0 >> VecAXPY 800 1.0 8.6160e-0113.6 3.36e+09 1.0 0.0e+00 0.0e+00 >> 0.0e+00 0 2 0 0 0 6 3 0 0 0 *247787 448304* 0 0.00e+00 >> 0 0.00e+00 100 >> VecAYPX 398 1.0 1.6831e+0031.1 1.67e+09 1.0 0.0e+00 0.0e+00 >> 0.0e+00 0 1 0 0 0 5 1 0 0 0 63107 77030 0 0.00e+00 0 >> 0.00e+00 100 >> VecPointwiseMult 402 1.0 3.8729e-01 9.3 8.43e+08 1.0 0.0e+00 0.0e+00 >> 0.0e+00 0 0 0 0 0 2 1 0 0 0 138502 262413 0 0.00e+00 0 >> 0.00e+00 100 >> VecScatterBegin 400 1.0 1.1947e+0035.1 0.00e+00 0.0 3.7e+05 6.1e+04 >> 0.0e+00 0 0 62 54 0 5 0100100 0 0 0 0 0.00e+00 0 >> 0.00e+00 0 >> VecScatterEnd 400 1.0 6.2969e+00 8.8 0.00e+00 0.0 0.0e+00 0.0e+00 >> 0.0e+00 0 0 0 0 0 10 0 0 0 0 0 0 0 0.00e+00 0 >> 0.00e+00 0 >> PCApply 402 1.0 3.8758e-01 9.3 8.43e+08 1.0 0.0e+00 0.0e+00 >> 0.0e+00 0 0 0 0 0 2 1 0 0 0 138396 262413 0 0.00e+00 0 >> 0.00e+00 100 >> >> --------------------------------------------------------------------------------------------------------------------------------------------------------------- >> >> >> On Sat, Jan 22, 2022 at 11:10 AM Junchao Zhang <junchao.zh...@gmail.com> >> wrote: >> >>> >>> >>> >>> On Sat, Jan 22, 2022 at 10:04 AM Mark Adams <mfad...@lbl.gov> wrote: >>> >>>> Logging GPU flops should be inside of PetscLogGpuTimeBegin()/End() >>>> right? >>>> >>> No, PetscLogGpuTime() does not know the flops of the caller. >>> >>> >>>> >>>> On Fri, Jan 21, 2022 at 9:47 PM Barry Smith <bsm...@petsc.dev> wrote: >>>> >>>>> >>>>> Mark, >>>>> >>>>> Fix the logging before you run more. It will help with seeing the >>>>> true disparity between the MatMult and the vector ops. >>>>> >>>>> >>>>> On Jan 21, 2022, at 9:37 PM, Mark Adams <mfad...@lbl.gov> wrote: >>>>> >>>>> Here is one with 2M / GPU. Getting better. >>>>> >>>>> On Fri, Jan 21, 2022 at 9:17 PM Barry Smith <bsm...@petsc.dev> wrote: >>>>> >>>>>> >>>>>> Matt is correct, vectors are way too small. >>>>>> >>>>>> BTW: Now would be a good time to run some of the Report I >>>>>> benchmarks on Crusher to get a feel for the kernel launch times and >>>>>> performance on VecOps. >>>>>> >>>>>> Also Report 2. >>>>>> >>>>>> Barry >>>>>> >>>>>> >>>>>> On Jan 21, 2022, at 7:58 PM, Matthew Knepley <knep...@gmail.com> >>>>>> wrote: >>>>>> >>>>>> On Fri, Jan 21, 2022 at 6:41 PM Mark Adams <mfad...@lbl.gov> wrote: >>>>>> >>>>>>> I am looking at performance of a CG/Jacobi solve on a 3D Q2 >>>>>>> Laplacian (ex13) on one Crusher node (8 GPUs on 4 GPU sockets, MI250X >>>>>>> or is >>>>>>> it MI200?). >>>>>>> This is with a 16M equation problem. GPU-aware MPI and non GPU-aware >>>>>>> MPI are similar (mat-vec is a little faster w/o, the total is about the >>>>>>> same, call it noise) >>>>>>> >>>>>>> I found that MatMult was about 3x faster using 8 cores/GPU, that is >>>>>>> all 64 cores on the node, then when using 1 core/GPU. With the same size >>>>>>> problem of course. >>>>>>> I was thinking MatMult should be faster with just one MPI process. >>>>>>> Oh well, worry about that later. >>>>>>> >>>>>>> The bigger problem, and I have observed this to some extent with the >>>>>>> Landau TS/SNES/GPU-solver on the V/A100s, is that the vector operations >>>>>>> are >>>>>>> expensive or crazy expensive. >>>>>>> You can see (attached) and the times here that the solve is >>>>>>> dominated by not-mat-vec: >>>>>>> >>>>>>> >>>>>>> ------------------------------------------------------------------------------------------------------------------------ >>>>>>> Event Count Time (sec) Flop >>>>>>> --- Global --- --- Stage ---- *Total GPU * - >>>>>>> CpuToGpu - - GpuToCpu - GPU >>>>>>> Max Ratio Max Ratio Max Ratio Mess >>>>>>> AvgLen Reduct %T %F %M %L %R %T %F %M %L %R *Mflop/s Mflop/s* >>>>>>> Count Size Count Size %F >>>>>>> >>>>>>> --------------------------------------------------------------------------------------------------------------------------------------------------------------- >>>>>>> 17:15 main= >>>>>>> /gpfs/alpine/csc314/scratch/adams/petsc/src/snes/tests/data$ grep >>>>>>> "MatMult >>>>>>> 400" jac_out_00*5_8_gpuawaremp* >>>>>>> MatMult 400 1.0 *1.2507e+00* 1.3 1.34e+10 1.1 3.7e+05 >>>>>>> 1.6e+04 0.0e+00 1 55 62 54 0 27 91100100 0 *668874 0* >>>>>>> 0 0.00e+00 0 0.00e+00 100 >>>>>>> 17:15 main= >>>>>>> /gpfs/alpine/csc314/scratch/adams/petsc/src/snes/tests/data$ grep >>>>>>> "KSPSolve >>>>>>> 2" jac_out_001*_5_8_gpuawaremp* >>>>>>> KSPSolve 2 1.0 *4.4173e+00* 1.0 1.48e+10 1.1 3.7e+05 >>>>>>> 1.6e+04 1.2e+03 4 60 62 54 61 100100100100100 *208923 1094405* >>>>>>> 0 0.00e+00 0 0.00e+00 100 >>>>>>> >>>>>>> Notes about flop counters here, >>>>>>> * that MatMult flops are not logged as GPU flops but something is >>>>>>> logged nonetheless. >>>>>>> * The GPU flop rate is 5x the total flop rate in KSPSolve :\ >>>>>>> * I think these nodes have an FP64 peak flop rate of 200 Tflops, so >>>>>>> we are at < 1%. >>>>>>> >>>>>> >>>>>> This looks complicated, so just a single remark: >>>>>> >>>>>> My understanding of the benchmarking of vector ops led by Hannah was >>>>>> that you needed to be much >>>>>> bigger than 16M to hit peak. I need to get the tech report, but on 8 >>>>>> GPUs I would think you would be >>>>>> at 10% of peak or something right off the bat at these sizes. Barry, >>>>>> is that right? >>>>>> >>>>>> Thanks, >>>>>> >>>>>> Matt >>>>>> >>>>>> >>>>>>> Anway, not sure how to proceed but I thought I would share. >>>>>>> Maybe ask the Kokkos guys if the have looked at Crusher. >>>>>>> >>>>>>> Mark >>>>>>> >>>>>> -- >>>>>> 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/~knepley/> >>>>>> >>>>>> >>>>>> <jac_out_001_kokkos_Crusher_6_8_gpuawarempi.txt> >>>>> >>>>> >>>>> <jac_out_001_kokkos_Crusher_5_8_notpl.txt> >> <jac_out_001_kokkos_Crusher_6_8_notpl.txt> >> >> >>