EveryDream2trainer/doc/OPTIMIZER.md

Advanced optimizer tweaking

You can set advanced optimizer settings using this arg:

--optimizer_config optimizer.json

or in train.json

"optimizer_config": "optimizer.json"

A default optimizer.json is supplied which you can modify.

This extra json file allows expanded tweaking.

If you do not set optimizer_config at all or set it to null in train.json, the defaults are adamw8bit with standard betas of (0.9,0.999), weight decay 0.01, and epsilon 1e-8.

Optimizers

In optimizer.json the you can set independent optimizer settings for both the text encoder and unet. If you want shared settings, just fill out the base section and leave text_encoder_overrides properties null an they will be copied from the base section.

If you set the text_encder_lr_scale property, the text encoder will be trained with a multiple of the Unet learning rate if it the LR is being copied. If you explicitly set the text encoder LR, the text_encder_lr_scale is ignored. text_encder_lr_scale is likely to be deprecated in the future, but now is left for backwards compatibility.

For each of the unet and text_encoder sections, you can set the following properties:

optimizer value is the type of optimizer to use. Below are the supported optimizers.

• adamw

Standard full precision AdamW optimizer exposed by PyTorch. Not recommended. Slower and uses more memory than adamw8bit. Widely documented on the web.

• adamw8bit

Tim Dettmers / bitsandbytes AdamW 8bit optimizer. This is the default and recommended setting. Widely documented on the web.

• lion

Lucidrains' implementation of the lion optimizer. Click links to read more. Epsilon is not used by lion.

Recommended settings for lion based on the paper are as follows:

"optimizer": "adamw8bit",
    "lr": 1e-7,
    "lr_scheduler": "constant",
    "betas": [0.9, 0.999],
    "epsilon": 1e-8,
    "weight_decay": 0.10

The recommendations are based on "1/10th LR" but "10x the weight decay" compared to AdamW when training diffusion models. There are no known recommendations for the CLIP text encoder. Lion converges quickly, so take care with the learning rate, and even lower learning rates may be effective.

Optimizer parameters

LR can be set in optimizer.json and excluded from the main CLI arg or train.json but if you use the main CLI arg or set it in the main train.json it will override the setting. This was done to make sure existing behavior will not break. To set LR in the optimizer.json make sure to delete "lr": 1.3e-6 in your main train.json and exclude the CLI arg.

The text encoder LR can run at a different value to the Unet LR. This may help prevent over-fitting, especially if you're training from SD2 checkpoints.

Text Encoder freezing

If you're training SD2.1 you will likely experience great benefit from partially freezing the text encoder. You can control text encoder freezing using the text_encoder_freezing block in your optimizer.json:

    "text_encoder_freezing": {
        "freeze_embeddings": true,
        "freeze_front_n_layers": -6,
        "freeze_final_layer_norm": false
    }

The SD2.1 text encoder is arranged as follows:

embeddings -> CLIP text encoder (23 layers) -> final layer norm

(The SD1.5 text encoder is similar but it has only 12 CLIP layers.) Typically you would apply freezing starting from the left and moving to the right, although it might be interesting to experiment with different freezing patterns. You can control this using the following parameters:

• freeze_embeddings freezes the front 2 layers (the text embeddings - recommend).
• freeze_front_n_layers freezes the front N layers of the CLIP text encoder. You can also pass null to leave the CLIP layers unfrozen, or negative values to count from the back. In the example above, -6 will freeze all but the last 6 layers.
• freeze_final_layer_norm freezes the parameters for the text encoder's final LayerNorm operation.

Recommended settings for SD2.1 are provided in optimizerSD21.json: frozen embeddings, all CLIP layers frozen except for the last 6, final layer norm unfrozen. If you want to experiment, start by trying different values for freeze_front_n_layers: -2 is slower but seems to produce a higher quality model, whereas -10 is faster but can be more difficult to control.

General Beta, weight decay, epsilon, etc tuning

Betas, weight decay, and epsilon are documented in the AdamW paper and there is a wealth of information on the web, but consider those experimental to tweak.