Hi, I'm using the GMRES with ASM preconditioner with sub-domain solver ILU(2) to solve an elasticity problem. First, I use 16 cores to test the computation time, then use 32 cores to run the same code with the same parameters. But I just get about 10% speed up. From the log file I found that the computation time of KSPSolve() and MatSolve() just decrease a little bit. My PETSc version is 3.16.0 and use --with-debugging=0 when configure it. The matrix size is about 7*10^6. Some detail of the log is shown below: 16-cores: ------------------------------------------------------------------------------------------------------------------------ Event Count Time (sec) Flop --- Global --- --- Stage ---- Total Max Ratio Max Ratio Max Ratio Mess AvgLen Reduct %T %F %M %L %R %T %F %M %L %R Mflop/s ------------------------------------------------------------------------------------------------------------------------ MatMult 664 1.0 5.0794e+01 1.6 2.70e+10 1.1 7.1e+04 4.8e+04 1.0e+00 7 13 49 20 0 7 13 49 20 0 8010 MatSolve 663 1.0 1.9868e+02 1.1 1.43e+11 1.1 0.0e+00 0.0e+00 0.0e+00 33 70 0 0 0 33 70 0 0 0 10932 MatLUFactorNum 1 1.0 6.1501e+00 1.1 1.40e+10 1.1 0.0e+00 0.0e+00 0.0e+00 1 7 0 0 0 1 7 0 0 0 35056 MatILUFactorSym 1 1.0 1.5566e+01 1.2 0.00e+00 0.0 0.0e+00 0.0e+00 0.0e+00 2 0 0 0 0 2 0 0 0 0 0 KSPSetUp 2 1.0 5.9627e-03 1.9 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 KSPSolve 1 1.0 2.5168e+02 1.0 1.90e+11 1.1 1.4e+05 4.8e+04 1.3e+03 44 93 98 40 89 44 93 98 40 90 11437 KSPGMRESOrthog 641 1.0 1.8980e+01 1.7 1.82e+10 1.1 0.0e+00 0.0e+00 6.4e+02 3 9 0 0 43 3 9 0 0 44 14578 PCSetUp 2 1.0 2.2480e+01 1.1 1.40e+10 1.1 5.3e+02 6.5e+05 7.0e+00 4 7 0 2 0 4 7 0 2 0 9591 PCSetUpOnBlocks 1 1.0 2.1555e+01 1.1 1.40e+10 1.1 0.0e+00 0.0e+00 0.0e+00 3 7 0 0 0 3 7 0 0 0 10002 PCApply 663 1.0 2.0296e+02 1.1 1.43e+11 1.1 7.0e+04 4.8e+04 1.0e+00 33 70 49 20 0 33 70 49 20 0 10701 PCApplyOnBlocks 663 1.0 1.9908e+02 1.1 1.43e+11 1.1 0.0e+00 0.0e+00 0.0e+00 33 70 0 0 0 33 70 0 0 0 10910 32-cores: ------------------------------------------------------------------------------------------------------------------------ Event Count Time (sec) Flop --- Global --- --- Stage ---- Total Max Ratio Max Ratio Max Ratio Mess AvgLen Reduct %T %F %M %L %R %T %F %M %L %R Mflop/s ------------------------------------------------------------------------------------------------------------------------ MatMult 671 1.0 4.7602e+01 2.0 1.39e+10 1.1 1.7e+05 2.8e+04 1.0e+00 7 13 49 23 0 7 13 49 23 0 8637 MatSolve 670 1.0 1.7800e+02 1.1 7.56e+10 1.1 0.0e+00 0.0e+00 0.0e+00 33 71 0 0 0 33 71 0 0 0 12544 MatLUFactorNum 1 1.0 3.5714e+00 1.1 7.16e+09 1.1 0.0e+00 0.0e+00 0.0e+00 1 7 0 0 0 1 7 0 0 0 60743 MatILUFactorSym 1 1.0 8.4088e+00 1.2 0.00e+00 0.0 0.0e+00 0.0e+00 0.0e+00 2 0 0 0 0 2 0 0 0 0 0 KSPSetUp 2 1.0 3.8060e-03 1.5 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 KSPSolve 1 1.0 2.1680e+02 1.0 9.95e+10 1.1 3.5e+05 2.8e+04 1.3e+03 44 93 98 47 89 44 93 98 47 90 13592 KSPGMRESOrthog 648 1.0 1.6999e+01 2.0 9.39e+09 1.1 0.0e+00 0.0e+00 6.5e+02 2 9 0 0 43 2 9 0 0 44 16450 PCSetUp 2 1.0 1.2439e+01 1.1 7.16e+09 1.1 1.3e+03 3.7e+05 7.0e+00 2 7 0 2 0 2 7 0 2 0 17440 PCSetUpOnBlocks 1 1.0 1.1876e+01 1.1 7.16e+09 1.1 0.0e+00 0.0e+00 0.0e+00 2 7 0 0 0 2 7 0 0 0 18267 PCApply 670 1.0 1.8235e+02 1.1 7.56e+10 1.1 1.7e+05 2.7e+04 1.0e+00 34 71 49 23 0 34 71 49 23 0 12245 PCApplyOnBlocks 670 1.0 1.7838e+02 1.1 7.56e+10 1.1 0.0e+00 0.0e+00 0.0e+00 33 71 0 0 0 33 71 0 0 0 12517 Hope you can help me! Best Regards, Yujie