GAMG without any options is using MatTransposeMatMult (in petsc-dev) during setup at line 1031 of agg.c. What I find is that this operation takes up a majority of the total setup time, and doesn't scale well. Is there anything that can be done about this?
I am a little surprised that it is taking significantly more time than the RAP construction of the coarse grid operators done by MatPtAP. On 1 processor, for example, it takes 5% of the setup time, and on 8 processors it takes ~4%. The MatTransposeMatMult, on the other hand, takes 67% of setup on 1 processor and 71% of setup on 8. I've attached the log_summary for 1 processor and 8 processors. You can also see that the solve time is completely eclipsed by the setup time. Regards, John -------------- next part -------------- A non-text attachment was scrubbed... Name: gamg_np1.out Type: application/octet-stream Size: 14732 bytes Desc: not available URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120817/50858c8c/attachment-0002.obj> -------------- next part -------------- A non-text attachment was scrubbed... Name: gamg_np8.out Type: application/octet-stream Size: 15496 bytes Desc: not available URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120817/50858c8c/attachment-0003.obj>
