<div class="gmail_quote">On Thu, Nov 17, 2011 at 11:17, Rongliang Chen <span dir="ltr"><<a href="mailto:rongliang.chan@gmail.com">rongliang.chan@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<div id=":222">In my log_summary output, I found that nearly 80% of the total time is spent on KSPGMRESOrthog. I think this does not make sense ( the log_summary output followed). Who has any idea about this?<br></div></blockquote>
<div><br></div><div>Reductions are very expensive relative to everything else on the coarse level. You can try more levels or a different coarse level solver. You can also likely get away with solving the coarse problem inexactly.</div>
<div><br></div><div>Alternatively, you can try getting Chebychev to help you out. Use -ksp_chebychev_estimate_eigenvalues to tune Chebychev (possibly to target a specific part of the spectrum).</div><div><br></div><div><a href="http://www.mcs.anl.gov/petsc/snapshots/petsc-dev/docs/manualpages/KSP/KSPChebychevSetEstimateEigenvalues.html">http://www.mcs.anl.gov/petsc/snapshots/petsc-dev/docs/manualpages/KSP/KSPChebychevSetEstimateEigenvalues.html</a></div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;"><div id=":222"><br>Another question, I am using the two-level asm precondtioner. On the coarse level I use one-level asm preconditioned GMRES to solve a coarse problem. So both the fine level solver and coarse level solver call the function KSPGMRESOrthog. In the log_summary output, I just know the total time spent on KSPGMRESOrthog and how can I know how much time is spent on the coarse level KSPGMRESOrthog and how much is spent on fine level KSPGMRESOrthog? Thanks.</div>
</blockquote></div><br><div>I assume you are using PCMG for this, so you can add -pc_mg_log to profile the time on each level independently. You seem to have many KSPGMRESOrthog steps per fine-level PCApply, so I think most of the time is in the coarse level.</div>