[Dune] [#742] performace loss between 1.2.2 and 2.0 (Attachment added)

[Dune]

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User who did this - Andreas Dedner (dedner) 

Attached to Project - Dune
Summary - performace loss between 1.2.2 and 2.0
Task Type - Bug Report
Category - Dune Modules
Status - New
Assigned To - 
Operating System - Unspecified / All
Severity - High
Priority - Urgent
Reported Version - SVN (pre2.0)
Due in Version - 2.0
Due Date - Undecided
Details - There is a significant performance loss between the
release 1.2.2 and 2.0. This can for example be seen
using the finitevolume test in the dune-grid-howto.
There are at least 2 issues we found:
1) in common/fvector.hh: the use of memcpy
   in the copy constructor and assignment operator 
   leads to about 20% loss. It is probably only
   a good idea for large vectors - but FieldVectors
   are quite often small. This was introduced in
   rev. 5874.
2) The second issue are changes in Yasp from rev. 6005.
   A patch reverting some of these changes is attached.
   With the patch applied we gain about 50%.
   They concern the reasonable separation of the
   Intersection from the IntersectionIterator but 
   perhaps the use of the shared_ptr cost too much 
   performance. 

Summary (using YaspGrid<2>)
dune-common, dune-grid: releases/1.2.2
dune-grid-hwoto: releases/1.2
a:                   2m52.759s 2m52.432s 2m52.169s   | 170s
------------------------------------------
dune-common, dune-grid: trunk
dune-grid-howto: trunk and releases/1.2:
b: howto trunk:      6m17.540s 6m03.663s 6m09.943s   | 370s
c: howto 1.2:        6m07.869s 6m12.032s 6m11.272s   | 370s
d: howto trunk no mc:5m04.990s 5m15.163s 5m07.877s   | 310s
e: howto 1.2 no mc:  5m35.168s 5m41.208s 5m40.581s   | 340s
f: howto trunk no mc
   and yasp patch:   2m22.751s 2m23.167s 2m20.617s   | 140s
------------------------------------------

1) memcopy (mc) leads to +9% (c/e) or +19% (b/d)
2) other changes between 1.2.2 and 2.0 lead to +80% (d/a)
   or +100% (e/a)
   This difference seems to be caused by the seperation of
   Intersection/IntersectionIterator in YaspGrid 
   (shared_ptr?)
   Applied patch is a partial revert of -r6005.
3) f/a<1 and d/e<1 is probably due to the new interface 
   methods (center...)
4) why b=c is somewhat unclear (would expect b/c<1)


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http://www.dune-project.org/flyspray/index.php?do=details&task_id=742

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