PPSSPP supports CHD files but it was recently discovered that if the CHD files are created with the createcd option, performance is degraded. On recent builds you see a warning on game launch if you're using this format.

If you've already converted your collection for using CHD (as many here would to save storage space), you can do the following to reconvert with createdvd to improve/correct performance:

For Linux:

1. Copy all your PSP CHD files into a single folder (if they're not already)

2. Install parallel (yum/apt/pamac install parallel, if you're using Linux I'll assume you can figure this out)

3. Run the following command to extract the CDs:

parallel chdman extractcd -i {} -o {.}.cue ::: *.chd

4. This will convert all the CHD files to BIN/CUE. Once done, then run:

parallel chdman createdvd -i {} -o {.}.chd ::: *.bin

And that's it. With parallel the process is really fast because it'll use n-1 threads (however many your CPU supports minus 1) to run the command in parallel instead of serializing the whole thing.

Only potential catch here is to be sure you have enough storage space, as the CHD files will extract to bin/cue larger than they were, and you'll likely need at least 2.5x the amount of space the existing CHDs take up in the path you're using.

For Windows

For Windows users, you can make a batch file with the following to extract:

for /r %%i in (*.chd) do chdman extractcd -i "%%i" -o "%%~ni.cue"

Save this file as extractcd.bat and place it in the ROM folder path.

And then another with:

for /r %%i in (*.bin) do chdman createdvd -i "%%i" -o "%%~ni.chd"

Save this file as createdvd.bat and place it in the ROM folder path.

Copy chdman.exe to the ROM folder path, then double click extractcd.bat, and when it finishes, double click createdvd.bat.

This will reconvert to CHD as DVD, but I'm not aware of any way to parallelize this in Windows, so it will take much longer.

When you're done, test your games, and so long as all is working you can delete the bin/cue files.