Hi!
I'm using one of my WIP (Babel tower) to compare the speed of 3.6.1a vs 3.7
beta5a vs 3.7 beta6. In this scene, the ground is an isosurface.

At 1024x768, no AA, no radiosity, 1 thread when applicable, i get the
following CPU time used (in seconds):

    3.6.1a           3.7 beta5a        3.7 beta6
(the scene as is)
    316.72         468.94(+48%)     469.45(+48%)
(with a point_light instead of an area_light)
     95.56         140.88(+47%)     138.33(+45%)
(with a plane instead of an isosurface)
     26.00          29.23(+12%)      27.02(+4%)

Clearly the isosurface is causing most of the overhead. Sticking with a
point light for now, i tried the following, knowing that max_gradient was
around 10.
(with evaluate 5.48, 1.29, 0.8)
     95.56         140.88(+47%)     138.33(+45%)
(with evaluate 4, 1.37, 0.2)
     86.81          99.92(+15%)      94.50(+9%)
(with a fixed max_gradient of 9.5)
    115.53         123.33(+7%)      119.97(+4%)

I tend to jump to the conclusion that in 3.6.1a using evaluate instead of a
fixed max_gradient leads to faster renders, more or less so depending on
the parameters (17% or 25% faster in the case above), whereas in the betas,
evaluate with nonoptimal parameters can lead to definitely slower renders
(approx. 15% slower above).

JYR

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