I have some trouble understanding remaining render time estimation. It seems that with adaptivity enabled you can't trust the information displayed, I have renders where it will show 2 hrs remaining rendertime for the first 5 passes, and then starts growing until it displays something around 20+ hours. If I disable adaptivity, the remaining estimation will behave like expected, it just counts down as time passes. The final result is that adaptivity adds a lot to the rendertime and the final rendertime increases by a factor of 10 on a big image here vs. a render without adaptivity. The final image may look slightly better but a factor of 10 for slightly less noise is in no way right. Plus, you can't rely on the estimated remaining time since it is misleading.
Given that adaptivity affects render times that much it should probably be moved from devel/debug section and not be enabled by default.
Seems odd.. the adaptivity really took 10times longer for same noise ratio (or passes) ? Or is that only based on estimate ?
No, this is what actually happens. The bad thing is that you may trust the rendertime estimate number, but beginning with pass 5 (probably due to adaptivity being rebalanced every 5 passes) it'll begin to climb up, and will keep rendering for 20 hrs.
My description of the issue is a bit convoluted but in simple words: render without adaptivity takes 2 hrs, render with adaptivity takes 20 hrs. Happens with daily 24-Apr-2016 and 1.4 RC4.
I can't share the scene, I know this is very unfortunate for you the devs. But I bet this can be observed on other scenes.