From e78bea89fd56a2c4d3a0d46cad8c78e5508505dd Mon Sep 17 00:00:00 2001 From: Wolfgang Bangerth Date: Tue, 25 Mar 2008 13:41:58 +0000 Subject: [PATCH] Show the new current profile and discuss it. git-svn-id: https://svn.dealii.org/trunk@15930 0785d39b-7218-0410-832d-ea1e28bc413d --- deal.II/examples/step-22/doc/intro.dox | 34 ++++++++++++++++---------- 1 file changed, 21 insertions(+), 13 deletions(-) diff --git a/deal.II/examples/step-22/doc/intro.dox b/deal.II/examples/step-22/doc/intro.dox index 20cc99423d..e9af6c9c6d 100644 --- a/deal.II/examples/step-22/doc/intro.dox +++ b/deal.II/examples/step-22/doc/intro.dox @@ -617,23 +617,28 @@ zero through three in 3d is shown here: @image html step-22.profile-3.png -As can be seen, at this refinement level approximately half of the -instruction count is spent on matrix assembly and sparse ILU computation (left -half), one third on the actual solver (the SparseILU::vmult calls in -the center right), and the rest on other things. Since floating point +As can be seen, at this refinement level approximately one sixth of the +instruction count is spent on matrix assembly and sparse ILU +computation (third quarter from left to right), about one half on the +actual solver (the SparseILU::vmult calls on +the left), and the rest on other things. Since floating point operations such as in the SparseILU::vmult calls typically take much longer than many of the logical operations and table lookups in matrix assembly, the fraction of the run time taken up by matrix assembly is -actually significantly less than half the total, as will become +actually significantly less than the fraction opf instructions, as will become apparent in the comparison we make in the results section. -For higher refinement levels, the greenesh boxes at the center right -representing the solver as well as the blue box at the top right -representing the reordering algorithm are going to grow at the expense -of the other parts of the program, since they don't scale -linearly. The fact that at this moderate refinement level (3168 cells -and 93176 degrees of freedom) matrix assembly requires about half the -instructions may therefore not be of such importance. +For higher refinement levels, the boxes representing the solver as +well as the beige box at the top right representing the stemming from +reordering algorithm are going to grow at the expense of the other +parts of the program, since they don't scale linearly. The fact that +at this moderate refinement level (3168 cells and 93176 degrees of +freedom) the linear solver already makes up more than half the +instructions is a good sign that most of the algorithms used in this +program are well-tuned and that major improvements in speeding up the +program are most likely not to come from hand-optimizing individual +aspects but by changing solver algorithms. We will address this point +in the discussion of results below as well. As a final point, and as a point of reference, the following picture also shows how the profile looked at an early stage of optimizing this @@ -645,4 +650,7 @@ As mentioned above, the runtime of this version was about twice as long as for the first profile, with the SparseILU decomposition taking up about 30% of the instruction count, and operations on the ill-suited CompressedSparsityPattern about 10%. Both these bottlenecks have since -been completely removed. +been completely removed with the exception of the use of the +CompressedSparsityPattern through the DoFRenumbering::Cuthill_McKee +algorithm. (The latter at least applies as of the time of writing of +this program; the problem may be solved in the future.) -- 2.39.5