ID 310270 - Mari's import speed in has regressed since 2.6v5

Problem summary
Mari's import speed in has regressed since 2.6v5 and should be reviewed internally for performance enhancements

Customer reported version
2.6v3 / 3.3v1
Customer reported platform
Scientific Linux

Steps to reproduce

Compare results in 2.6v5 and 3.3v1
1) Create an archive with the problematic geometry (197 UDIMs)

2) Create a single channel (Size 4k, Depth 8bit)

3) In the layer stack, right click > Import into Layer

4) Browse to where you have saved the image maps and Import

5) Wait for the import to complete and time how long it takes

Note: that you will experience UI waiting times in both 2.5v6 and 3.3v1, but will wait for a much longer time when importing the images in 3.3v1. It is also worth noting that you MUST create a new archive each time you test else Mari seems to cache data and importing these files is quicker.

Workaround
In your Mari preferences, please try setting your Mip-Mapping Generation to 'Fast' (Edit > Preferences > GPU > Baking and Projection). Please note that this will not impact UI speeds only importing.

Alternatively, to ensure that you are optimising your import times, you should import your images as the same colorspace as the channel you are wishing to import into. This will mean that the images do not need to be converted on import, significantly speeding up import times.

To do this:

1) Create your channel and select your channel colorspace, for instance, 'Linear'.
2) Right click on your channels palette and select 'Import into Layer Stack' (Or similarly, 'Import into New Channel')
3) In the Import dialog ensure that your colorspace matches that of the channel you are importing into.
4) Select 'Import All Patches'

From an in-house test, we imported 128 2K 16bit EXR images onto an object with the following results:

- Linear->Linear = 4m50s
- Linear -> sRGB = 7m47s

As you can see, even on our simple test, results drastically improved. If you do experience any issues with this or see different results with your own tests, please feel free to get in touch with us here in Support.

Reproduced by support
3.3v1 - Windows 7
3.2v1
3.1v3
3.0v4
3.0v1 - Windows 7

Earliest version tested
Regression 2.6v5. Currently unable to test across multiple operating systems as the archive cannot be uploaded to the network. Please assess during the investigation.

Expected behaviour
Mari should import images at the same speed as in 2.6. Users should also experience minimal UI lag.

Actual behaviour
Import times were vastly different on the first import of a fresh archive from 2.6 to 3.3v1.

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