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I will see if I can spare some time to take a look at this over the weekend.
Thorsten Froehlich
On 26.08.2020 05:17, DonF wrote:
> William F Pokorny <ano### [at] anonymous org> wrote:
>
> DETAILS:
>
> Description of the SPEC test case:
>
> POV-Ray is a free and open source ray-tracing application. The CPU2017
> version is based on POV-Ray version 3.7.
>
> The benchmark renders a 2560 x 2048 pixel image of a chess board, with the
> pieces placed on the board in the starting position. The rendered scene
> image is saved as a Targa (.tga) file.
>
> This output image is compared with the reference output image using the
> SPEC utility [1]imagevalidate, which calculates a the structural
> similarity (SSIM) index between corresponding 8x8 groups of pixels in each
> image. The SSIM index has a range of -1 (maximal difference) to 1
> (identical). The benchmark requires that all computed SSIM indices be
> greater than 0.996 in order for the run to be considered successful.
>
> A log of the execution is also generated, but its contents are not used to
> validate correction operation of the benchmark.
>
> POV-Ray (which became 511.povray_r) was contributed to CPU2017 by one of
> the developers, Thorsten Froehlich, under the GNU Affero License v3.
>
>
> Performance of SPEC2017 REF sized test case:
>
> Sample performance difference using Intel compiler on a Skylake system
> with the spec2017 REF size test case, but most compilers on most platforms,
> including x86 or ARM platforms, can see similar large performance differences
> with just this one slight numerical difference in J.
>
> If J turns out to be zero, or if reset. 218 seconds.
> Without resetting J to zero when close to zero. 349 seconds. 60% slower.
>
> Both output images validated successfully using the SPEC imagevalidate method,
> but the one output image took much longer to generate.
>
>
> Input .ini file used for the SPEC2017 REF sized test case:
>
> Width=2560
> Height=2048
> All_Console=On
> All_File=SPEC-benchmark.log
> Antialias_Depth=3
> Antialias=On
> Antialias_Threshold=0.3
> Bits_Per_Color=8
> Bounding_Threshold=1
> Bounding=On
> Buffer_Output=Off
> Buffer_Size=0
> Clock=0
> Continue_Trace=Off
> Create_Histogram=Off
> Cyclic_Animation=Off
> Debug_Console=Off
> Display=Off
> Display_Gamma=1.0
> Draw_Vistas=Off
> Fatal_Console=On
> Fatal_Error_Command=
> Fatal_Error_Return=I
> Field_Render=Off
> Final_Clock=1
> Final_Frame=1
> Histogram_Name=
> Histogram_Grid_Size=0.0
> Initial_Clock=0
> Initial_Frame=1
> Include_Header=
> Input_File_Name=SPEC-benchmark-ref.pov
> Jitter_Amount=0.30
> Jitter=Off
> Light_Buffer=On
> Odd_Field=Off
> Output_Alpha=Off
> Output_File_Name=SPEC-benchmark.tga
> Output_File_Type=t
> Palette=3
> Pause_When_Done=Off
> Post_Frame_Command=
> Post_Frame_Return=I
> Post_Scene_Command=
> Post_Scene_Return=I
> Preview_End_Size=1
> Preview_Start_Size=1
> Pre_Frame_Command=
> Pre_Frame_Return=I
> Pre_Scene_command=
> Pre_Scene_Return=I
> Quality=9
> Remove_Bounds=Off
> Render_Console=On
> Sampling_Method=1
> Split_Unions=Off
> Statistic_Console=On
> Subset_End_Frame=1
> Subset_Start_Frame=1
> Test_Abort_Count=0
> Test_Abort=Off
> User_Abort_Command=
> User_Abort_Return=I
> Verbose=Off
> Version=3.5
> Video_Mode=0
> Vista_Buffer=On
> Warning_Console=Off
>
>
> Description of input .pov:
>
> // Persistence Of Vision raytracer sample file.
> // POV-Ray scene description for chess board.
> // By Ville Saari
> // Copyright (c) 1991 Ferry Island Pixelboys
> //
> // This scene has 430 primitives in objects and 41 in bounding shapes and
> // it takes over 40 hours to render by standard amiga.
> //
> // If you do some nice modifications or additions to this file, please send
> // me a copy. My Internet address is: vsa### [at] niksulahutfi
> //
> // -w320 -h240
> // -w800 -h600 +a0.3
>
> // Note : CHESS2.POV was created from Ville Saari's chess.pov
> // -- Dan Farmer 1996
> // - Cchanged textures
> // - Added camera blur and changed focal length
> // - Use sky sphere
> // - Modularized the code
> // - Added felt pads to bottom of pieces
>
> // remaining manual bounding commented out by Bob Hughes, August 31, 2001
>
>
> Execution Trace:
>
> With my own little debug trace through the Compute_Quadric_BBox() routine of
> file quadrics.cpp using the SPEC test case, I see 19 calls to the
> Compute_Quadric_BBox() routine.
>
> All calls to Compute_Quadric_BBox() execute one of the many
> "Check for xxxxxxx (?-axis)" code blocks, EXCEPT the one case where
> "J is recalculated, ends up being close to zero, but not quite zero,
> and is not reset". In this one case, none of the "Check ..." code blocks are
> executed, the "Add translation" and the "Beware of bounding boxes to large"
> are executed, and large values for BBox.Lengths the BBox.Lower_Left values
> are used.
>
>
> Executed code when J is "recalculated" and ends up being exactly equal to
> 0.0 (or is reset to zero if close) for the 1 of 19 cases that differed:
>
> J was recalculated to J=4.440892e-16,
> and then reset to 0.0 with modified code I added.
>
> Check for cone (y-axis).
> Add translation.
> Quadric->BBox.Lengths 0 to 2: 4.333333 3.500000 4.333333
> Quadric->BBox.Lower_Left 0 to 2: -2.166667 8.000000 -2.166667
>
>
> Executed code when J is "recalculated" and ends up NOT quite being exactly
> equal to 0.0:
>
> Add translation.
> Beware of bounding boxes to large.
> Quadric->BBox.Lengths 0 to 2: 20000000000.000000 20000000000.000000
> 20000000000.000000
> Quadric->BBox.Lower_Left 0 to 2: -10000000000.000000 -10000000000.000000
> -10000000000.000000
>
> For the faster executing run, note that the "Beware of bounding boxes to
> large" code block is still executed for 8 of the 19 calls to
> Compute_Quadric_BBox(), and even when "Beware of bounding boxes to large"
> is NOT called, the large BBox values may be still be set or inherited.
> For this faster test case, 12 of the 19 calls to
> Compute_Quadric_BBox() ended up with large BBox values, so having the
> large BBox values is not unusual, but for the one call where J was not
> reset when perhaps it could/should have been reset, the large BBox values
> were one of the differences encountered between the slower and faster
> runs.
>
>
> Portion of log file results (not used for SPEC verification) for the
> fast and slow execution.
>
> Fast execution with recalculated J reset to zero when it is close to zero:
> 218 seconds.
>
> Image Resolution 2560 x 2048
> ----------------------------------------------------------------------------
> Pixels: 5242880 Samples: 56705552 Smpls/Pxl: 10.82
> Rays: 114705211 Saved: 1162288 Max Level: 5/5
> ----------------------------------------------------------------------------
> Ray->Shape Intersection Tests Succeeded Percentage
> ----------------------------------------------------------------------------
> Box 16019108 16019107 100.00
> Cone/Cylinder 12818313 3292990 25.69
> CSG Intersection 1100588845 111370367 10.12
> CSG Union 88374684 76631294 86.71
> Plane 4514922317 2468835793 54.68
> Quadric 330552192 175746735 53.17
> Sphere 289188952 70116199 24.25
> Bounding Box 2485773879 745702120 30.00
> Light Buffer 1823322702 1064180254 58.36
> ----------------------------------------------------------------------------
>
>
> Slow execution with recalculated J NOT reset to zero when it was close
> to zero: 349 seconds.
>
> Note the large increase in "Tests" for many of the
> "Ray->Shape Intersestion" values, such as CSG Intersection, Plane,
> Quadric, and Sphere, (flagged with **) which presumably
> results in the large increase in execution time.
>
> Image Resolution 2560 x 2048
> ----------------------------------------------------------------------------
> Pixels: 5242880 Samples: 56705552 Smpls/Pxl: 10.82
> Rays: 114705211 Saved: 1162288 Max Level: 5/5
> ----------------------------------------------------------------------------
> Ray->Shape Intersection Tests Succeeded Percentage
> ----------------------------------------------------------------------------
> Box 16019108 16019107 100.00
> Cone/Cylinder 12818313 3292990 25.69
> CSG Intersection 2573044515** 113104449 4.40
> CSG Union 88374684 76631294 86.71
> Plane 5987377987** 3804982796 63.55
> Quadric 1066780027** 285487345 26.76
> Sphere 9123922972** 73475346 0.81
> Bounding Box 2368729644 732816314 30.94
> Light Buffer 2057730695 1350487574 65.63
> ----------------------------------------------------------------------------
>
>
>
>> My quick take is those initial EPSILONs (1e-10 in POV-Ray) should be
>> more like what I'm using in my personal povr branch (gkDBL_epsilon at
>> ~ 4.4e-16)
>
> Based on my observations, 4.4e-16 might be a little too restrictive to catch
> many of the obvious "close to zero values". An EPSILON of 1e-10 may,
> or may not, be too lax, but I think 4.4e-16 would be too restrictive.
> The recalculated values of J that were not close to zero for this case,
> and hence didn't need to be reset were either -1.0, or already 0.0.
>
>
>
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