[Bf-cycles] Hair Rendering and Steps?

Zauber Paracelsus zauber at gridmail.org
Thu Feb 19 04:48:41 CET 2015

Okay, this post is about a performance oddity that I have noticed with 
hair rendering.

What I am seeing deals with the Steps property, under the Render panel 
in hair properties.  While tinkering with it I found that each 1 step 
reduction results in the render's memory usage being reduced by half, 
which makes sense given the description.  As an added bonus, it reduces 
the build time for the render.

However, on the flip side I have found that lower values seem to 
increase the final render time.  Below is the rendering times, measured 
on one of the current builds off of buildbot (hash fda1198)

GPU Render:
3 Steps: 12.20s
2 Steps: 12.90s
1 Step:  16.81s
0 Steps: 28.04s

CPU Render:
3 Steps: 23.60s
2 Steps: 27.15s
1 Step:  38.96s
0 Steps: 80.24s

Now, this isn't quite what I was expecting.  If there's less 
geometry/data to process, then in theory shouldn't the render times be 
going down?

Is this expected, or have I spotted a performance flaw or regression?

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