fzalfa wrote:
hello
i have try the latest Blender provided in the previous topic, support up to 8 cpu is great
i cannot resist to do some benchmark and i observe some strange behaviour in multithread
i use the same test scene between the Octane2 dual R12k and the O2k 8 R10k 250
the first try i do with the O2k was about 1m17s75.....slower than my Octane2.... ??
parametters was, 8 threads, render tile 4x4
at the begining of the rendering all the cpu are loaded, and gradualy as therendering progress, the used cpu number goes lowering. why ??
at the begining the rendering was very fast, and when the most rendering parts are done, the rendering brake seriousely
so i have found a solution, i adjuste the tile render zone as multiple of numbers of cpu, so this is the result with this mods:
8 threads, render tiles 8x8 done in 25s63...... awesome no ?
from to start to the end of the rendering, all the cpu are used....
regards & happy new year
Laurent
I'm I missing something deeper in this?
Because for me it looks obvious what’s going on here.
When there are less than 8 tiles left, some CPUs will be unused as they will not be able to pick any more tiles, right?
So at the end there will always be unused CPUs.
As the tiles completes, more and more CPUs will be unallocated until there is just one CPU doing the last tile.
So the total amount of processing power goes down when there is less than 8 tiles left, right?
So the trick is making enough tiles in the job so that the last 8 tiles is a very small percentage of the total number of tiles, thus affecting the job the least.
In your first example with 4x4 tiles (16) the last 8 tiles is half of the entire job, thus giving big impact on the job.
But in your second example 8x8 tiles (64) the last 8 tiles is just one 1/8 of the entire job, giving less impact on the job.
So your right in that more tiles are better but I don’t believe it has to be a multiple of the number of CPUs, for example, a job with 6x10 tiles are probably as fast as a job with 8x8 tiles.