[Bf-cycles] Proposal to remove tile size option

[Thomas Dinges]

Hi Mai,

Less UI options is always better in my opinion. From what I read online,
not optimal tile sizes are still one of the biggest error sources when
it comes to performance. If we can hide this logic from the user and do
it automatically, we should definitely do it.

Best regards,

Thomas


Am 05.01.2017 um 11:20 schrieb Mai Lavelle:
> Hi everyone,
>
> I'd like to propose the removal of the tile size setting. This setting
> can be hard for artists to set correctly, as how it affects
> performance is not always clear. While working with the split kernel
> I've found that in some situations there is no good choice, the user
> simply can't know all the factors in play, and will likely end up
> setting the tile size to something ridiculously large to compensate.
> There's also the situation of switching devices or machines, the size
> chosen for a file on one system when opened on another may no longer
> be the best choice.
>
> Being such an important factor in performance, along with the
> difficulty of setting it properly, I think that tile size should be
> chosen automatically by the render engine. Or rather, I think device
> work load should not be a user level setting.
>
> Implementation should be mostly straight forward. Idea is to decouple
> tile size from work load by using a fixed tile size such as 32x32 (or
> maybe provide a limited set of options) for all renders and have the
> path tracing logic acquire and render at once a number of tiles to
> saturate the device. This way artists don't need to worry about
> setting a good tile size, each device type will know how much work it
> needs and request that much work from the tile manager without user
> intervention.
>
> Changes to path tracing code should be pretty simple, mainly need to
> pass an array of sample ranges and their corresponding buffers to the
> kernel. For final renders the device could request multiple tile
> samples from the same tile to render at once. For preview one sample
> from multiple tiles would be rendered.
>
> The main problem I can see at the moment is the save buffers option,
> which expects the user set tile size to match exactly what tile size
> the render engine updates buffers with. A possible solution is to have
> the save buffer option query the render engine for which tile size it
> uses.
>
> Any input, either on implementation or reasons for or against doing
> this, would be much appreciated.
>
> Thanks,
>
> Mai
>
>
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