make timestep sampling behave in the standard way when huber loss is used

Author: recris

library/train_util.py

@@ -5124,34 +5124,27 @@ def save_sd_model_on_train_end_common(
 
 
 def get_timesteps_and_huber_c(args, min_timestep, max_timestep, noise_scheduler, b_size, device):
-
-    # TODO: if a huber loss is selected, it will use constant timesteps for each batch
-    # as. In the future there may be a smarter way
+    timesteps = torch.randint(min_timestep, max_timestep, (b_size,), device='cpu')
 
     if args.loss_type == "huber" or args.loss_type == "smooth_l1":
-        timesteps = torch.randint(min_timestep, max_timestep, (1,), device="cpu")
-        timestep = timesteps.item()
-
         if args.huber_schedule == "exponential":
             alpha = -math.log(args.huber_c) / noise_scheduler.config.num_train_timesteps
-            huber_c = math.exp(-alpha * timestep)
+            huber_c = torch.exp(-alpha * timesteps)
         elif args.huber_schedule == "snr":
-            alphas_cumprod = noise_scheduler.alphas_cumprod[timestep]
+            alphas_cumprod = torch.index_select(noise_scheduler.alphas_cumprod, 0, timesteps)
             sigmas = ((1.0 - alphas_cumprod) / alphas_cumprod) ** 0.5
             huber_c = (1 - args.huber_c) / (1 + sigmas) ** 2 + args.huber_c
         elif args.huber_schedule == "constant":
-            huber_c = args.huber_c
+            huber_c = torch.full((b_size,), args.huber_c)
         else:
             raise NotImplementedError(f"Unknown Huber loss schedule {args.huber_schedule}!")
-
-        timesteps = timesteps.repeat(b_size).to(device)
+        huber_c = huber_c.to(device)
     elif args.loss_type == "l2":
-        timesteps = torch.randint(min_timestep, max_timestep, (b_size,), device=device)
-        huber_c = 1  # may be anything, as it's not used
+        huber_c = None  # may be anything, as it's not used
     else:
         raise NotImplementedError(f"Unknown loss type {args.loss_type}")
-    timesteps = timesteps.long()
 
+    timesteps = timesteps.long().to(device)
     return timesteps, huber_c
 
 
@@ -5190,20 +5183,21 @@ def get_noise_noisy_latents_and_timesteps(args, noise_scheduler, latents):
     return noise, noisy_latents, timesteps, huber_c
 
 
-# NOTE: if you're using the scheduled version, huber_c has to depend on the timesteps already
 def conditional_loss(
-    model_pred: torch.Tensor, target: torch.Tensor, reduction: str = "mean", loss_type: str = "l2", huber_c: float = 0.1
+    model_pred: torch.Tensor, target: torch.Tensor, reduction: str, loss_type: str, huber_c: Optional[torch.Tensor]
 ):
 
     if loss_type == "l2":
         loss = torch.nn.functional.mse_loss(model_pred, target, reduction=reduction)
     elif loss_type == "huber":
+        huber_c = huber_c.view(-1,1,1,1)
         loss = 2 * huber_c * (torch.sqrt((model_pred - target) ** 2 + huber_c**2) - huber_c)
         if reduction == "mean":
             loss = torch.mean(loss)
         elif reduction == "sum":
             loss = torch.sum(loss)
     elif loss_type == "smooth_l1":
+        huber_c = huber_c.view(-1, 1, 1, 1)
         loss = 2 * (torch.sqrt((model_pred - target) ** 2 + huber_c**2) - huber_c)
         if reduction == "mean":
             loss = torch.mean(loss)