FG Calculation Slow down on last tiles

[NNois]

Hello,
I've a problem with all my renders and scenes, in every contexts:

The FG calculation part of rendered frames hugely slow down at let say 98%.
It's bizard, for example for 95% of a frame it takes like 1min and the 100% are reached at 3min
I've a height core processor machine, xsi 6,5 and the scenario is the same at every new project.
How can I configure the tile size of FG to reduce the problem and, by the way is it normal than an FG calculation lefts a sort of an unrendered grid for the last percentages of the calculation ?
Thanks

[thiago]

Should not slow down, but if the fgmap is huge, it can slow down when it starts to dump the .fgmap. And that's gonna depend on the speed of HD access or network access...
But the calculation itself should not slow down in the end. This happen to all scenes?

[alexyork]

i'm not 100% sure but if, for example, you have 4 cores to render a frame, the last bucket will only be rendered with 1 of those cores, so the time for that bucket to complete will be quadrupled. on some frames/stills that can increase rendertime hugely.

as i say i'm not 100% on this, perhaps MR subdivides the last bucket into however many cores you have, but i strongly doubt it does. it's something I've wanted for some time now. that "last bucket" can often be a right pain.

[thiago]

Reduce the tile size, you will have more tiles to render (which will render faster because it's a smaller area), so you will have more processors working simultaneously in more tiles.

[CiaranM]

Reduce the tile size, you will have more tiles to render (which will render faster because it's a smaller area), so you will have more processors working simultaneously in more tiles.

But, don't go too small, that will have the opposite effect! Depending on number of cores, you'll need to experiment to find the right balance between render speed and tile size.

[thiago]

But, don't go too small, that will have the opposite effect! Depending on number of cores, you'll need to experiment to find the right balance between render speed and tile size.

Absolutely right.