Performance testing shared vs. static libs

I wrote these tests to see how much slower it is to call into a sharedlibrary than it is to call into a static library.  My intuition wouldsay that shared is slower, of course, but by how much?These timings are calling a routine that simply increments an integer(it's only 8 instructions total), so the differences shown here arepretty much worst-case.  For example, if my test says that calling ashared library is 10% slower, but your routine is 80 instructions long(10x larger than mine), then for you, calling a shared library routinewould only be a 1% performance hit.The tests shown below were run on Linux 2.6, gcc 3.3.3 on an Athlon1800.  You can retrieve the test code from funcptrs-0.2.tar.gz on:   http://www.rinspin.com/bronson/code/gcc/COMPILED RESULTSShared vs. staticCalling a shared library routine is 1-20% slower, with the typicalperformance hit somewhere around 15%:  direct to shared library:      -O0=5%,  -01=20%, -O2=20%, -O3=1%,  -Os=10% slower  indirect to shared library:      -O0=10%, -01=15%, -O2=15%, -O3=15%, -Os=10% slowerPIC (position-independent code) vs. position dependent code:-fPIC (position independent code) doesn't affect the speed of the directfunction call at all (except for -Os, where it's 5% slower).  However,when calling via function pointer, -fPIC causes a 0 to 30% peformancehit (-O0=0%, -O1=10%, -O2=20%, -O3=30%, -Os=15% slower) overposition-dependent code.Static linking vs. compiling directly:As you would expect, statically linking to a routine in a libraryusually provides exactly the same performance as directly compiling theroutine into your program.  There are some exceptions, however:-O1 is 5% slower and -Os is 5% faster.  This seems really weird to me.Why would it be any different at all?CONCLUSIONYes, calling a shared library routine is slower.  But not much.  Fortrivial functions, it might be 30% slower worst case, 15% typical,depending on your code and optimization level.  For real-worldfunctions, as long as they're not used in the innermost loops, the delaycaused by calling into a shared library is negligible.    - ScottDATA:For -O0:  Directly calling a shared library routine is 5% slower than calling  it statically.  Indirect function call: (5% slower than direct)    Calling into a shared library is 10% slower than calling statically.        (i.e. calling a shared library function indirectly is 15% slower        than calling a static library function directly)           null: min=0.35936 max=0.37501 avg=0.36353     44.917%         direct: min=0.80486 max=0.82058 avg=0.80934    100.000%       dirshare: min=0.82967 max=0.87794 avg=0.84628    104.563%      dirstatic: min=0.80114 max=0.80580 avg=0.80432     99.379%   dirpicstatic: min=0.80263 max=0.82554 avg=0.80936    100.002%       indirect: min=0.83391 max=0.85256 avg=0.84431    104.320%     indirshare: min=0.91188 max=0.95370 avg=0.93296    115.273%    indirstatic: min=0.83172 max=0.86983 avg=0.84892    104.889% indirpicstatic: min=0.83234 max=0.87370 avg=0.84546    104.462%For -O1:  calling a shared library routine is 20% slower than calling  it statically (for both direct and indirect).  Directly calling a static library routine is 5% slower than calling  a routine that has been directly compiled in (?!).  This isreproducible.  For some reason, PIC causes a 10% performance hit in the indirect  call, but not in the direct call!           null: min=0.24641 max=0.25326 avg=0.24962     48.134%         direct: min=0.51562 max=0.51982 avg=0.51859    100.000%       dirshare: min=0.62994 max=0.63484 avg=0.63222    121.911%      dirstatic: min=0.54484 max=0.54833 avg=0.54584    105.254%   dirpicstatic: min=0.54667 max=0.55310 avg=0.55051    106.156%       indirect: min=0.53638 max=0.55393 avg=0.54647    105.377%     indirshare: min=0.63173 max=0.64108 avg=0.63423    122.299%    indirstatic: min=0.51710 max=0.52236 avg=0.51930    100.137% indirpicstatic: min=0.57687 max=0.57940 avg=0.57802    111.460%For -O2:  calling a shared library routine is 20% slower than calling  it statically (for both direct and indirect).  Directly calling a static library routine is 5% slower than calling  a routine that has been directly compiled in (?!).  This isreproducible.  For some reason, PIC causes a 20% performance hit in the indirect  call, but not in the direct call!           null: min=0.25051 max=0.25293 avg=0.25157     48.603%         direct: min=0.51552 max=0.52036 avg=0.51761    100.000%       dirshare: min=0.63215 max=0.63767 avg=0.63372    122.432%      dirstatic: min=0.51592 max=0.51873 avg=0.51756     99.991%   dirpicstatic: min=0.51541 max=0.52058 avg=0.51775    100.027%       indirect: min=0.51572 max=0.52056 avg=0.51831    100.136%     indirshare: min=0.60469 max=0.60900 avg=0.60630    117.135%    indirstatic: min=0.51512 max=0.51920 avg=0.51735     99.950% indirpicstatic: min=0.63046 max=0.64098 avg=0.63390    122.466%For -O3:  It doesn't matter if youre callind a shared library, static  library, or your own code, or -fPIC or not.  All direct calls  are very close to each other (about 1%).  We do see that indirectly calling your own code or a staticlibrary goes 10% faster than direct (as found in the previousbattery of tests).Indirectly calling a shared library takes 15% longer thanindirectly calling a static library (and 5% longer than directlycalling either static or shared).PIC continues to cause a 20% performance hit for indirect.           null: min=0.24947 max=0.25187 avg=0.25082     43.595%         direct: min=0.57265 max=0.57676 avg=0.57534    100.000%       dirshare: min=0.58120 max=0.58617 avg=0.58403    101.509%      dirstatic: min=0.57705 max=0.59201 avg=0.58076    100.942%   dirpicstatic: min=0.57274 max=0.57839 avg=0.57535    100.001%       indirect: min=0.51557 max=0.51962 avg=0.51780     89.999%     indirshare: min=0.60617 max=0.60948 avg=0.60813    105.699%    indirstatic: min=0.51572 max=0.51917 avg=0.51813     90.056% indirpicstatic: min=0.62970 max=0.63533 avg=0.63271    109.970%For -Os:Calling a shared library takes 10% longer than static (both direct andindirect)Calling a static library is 5% faster than calling direct code?!?!-fPIC causes a 5% performance hit direct and a 15% performance hitindirect.           null: min=0.25008 max=0.25290 avg=0.25153     43.712%         direct: min=0.57253 max=0.57886 avg=0.57543    100.000%       dirshare: min=0.62959 max=0.63425 avg=0.63178    109.793%      dirstatic: min=0.54431 max=0.54895 avg=0.54653     94.977%   dirpicstatic: min=0.57430 max=0.58078 avg=0.57699    100.270%       indirect: min=0.57590 max=0.57842 avg=0.57706    100.283%     indirshare: min=0.63282 max=0.63675 avg=0.63517    110.382%    indirstatic: min=0.57224 max=0.57681 avg=0.57524     99.966% indirpicstatic: min=0.65924 max=0.66185 avg=0.66071    114.819%