diff --git a/flux_train_network.py b/flux_train_network.py
index 26503df1f..def441559 100644
--- a/flux_train_network.py
+++ b/flux_train_network.py
@@ -381,8 +381,7 @@ def get_noise_pred_and_target(
             t5_attn_mask = None
 
         def call_dit(img, img_ids, t5_out, txt_ids, l_pooled, timesteps, guidance_vec, t5_attn_mask):
-            # if not args.split_mode:
-            # normal forward
+            # grad is enabled even if unet is not in train mode, because Text Encoder is in train mode
             with torch.set_grad_enabled(is_train), accelerator.autocast():
                 # YiYi notes: divide it by 1000 for now because we scale it by 1000 in the transformer model (we should not keep it but I want to keep the inputs same for the model for testing)
                 model_pred = unet(
@@ -395,44 +394,6 @@ def call_dit(img, img_ids, t5_out, txt_ids, l_pooled, timesteps, guidance_vec, t
                     guidance=guidance_vec,
                     txt_attention_mask=t5_attn_mask,
                 )
-            """
-            else:
-                # split forward to reduce memory usage
-                assert network.train_blocks == "single", "train_blocks must be single for split mode"
-                with accelerator.autocast():
-                    # move flux lower to cpu, and then move flux upper to gpu
-                    unet.to("cpu")
-                    clean_memory_on_device(accelerator.device)
-                    self.flux_upper.to(accelerator.device)
-
-                    # upper model does not require grad
-                    with torch.no_grad():
-                        intermediate_img, intermediate_txt, vec, pe = self.flux_upper(
-                            img=packed_noisy_model_input,
-                            img_ids=img_ids,
-                            txt=t5_out,
-                            txt_ids=txt_ids,
-                            y=l_pooled,
-                            timesteps=timesteps / 1000,
-                            guidance=guidance_vec,
-                            txt_attention_mask=t5_attn_mask,
-                        )
-
-                    # move flux upper back to cpu, and then move flux lower to gpu
-                    self.flux_upper.to("cpu")
-                    clean_memory_on_device(accelerator.device)
-                    unet.to(accelerator.device)
-
-                    # lower model requires grad
-                    intermediate_img.requires_grad_(True)
-                    intermediate_txt.requires_grad_(True)
-                    vec.requires_grad_(True)
-                    pe.requires_grad_(True)
-
-                    with torch.set_grad_enabled(is_train and train_unet): 
-                        model_pred = unet(img=intermediate_img, txt=intermediate_txt, vec=vec, pe=pe, txt_attention_mask=t5_attn_mask)
-            """
-
             return model_pred
 
         model_pred = call_dit(
@@ -551,6 +512,11 @@ def forward(hidden_states):
                 text_encoder.to(te_weight_dtype)  # fp8
                 prepare_fp8(text_encoder, weight_dtype)
 
+    def on_validation_step_end(self, args, accelerator, network, text_encoders, unet, batch, weight_dtype):
+        if self.is_swapping_blocks:
+            # prepare for next forward: because backward pass is not called, we need to prepare it here
+            accelerator.unwrap_model(unet).prepare_block_swap_before_forward()
+
     def prepare_unet_with_accelerator(
         self, args: argparse.Namespace, accelerator: Accelerator, unet: torch.nn.Module
     ) -> torch.nn.Module:
diff --git a/library/train_util.py b/library/train_util.py
index b23290663..1f591c422 100644
--- a/library/train_util.py
+++ b/library/train_util.py
@@ -13,17 +13,7 @@
 import shutil
 import time
 import typing
-from typing import (
-    Any,
-    Callable,
-    Dict,
-    List,
-    NamedTuple,
-    Optional,
-    Sequence,
-    Tuple,
-    Union
-)
+from typing import Any, Callable, Dict, List, NamedTuple, Optional, Sequence, Tuple, Union
 from accelerate import Accelerator, InitProcessGroupKwargs, DistributedDataParallelKwargs, PartialState
 import glob
 import math
@@ -146,12 +136,13 @@
 TEXT_ENCODER_OUTPUTS_CACHE_SUFFIX = "_te_outputs.npz"
 TEXT_ENCODER_OUTPUTS_CACHE_SUFFIX_SD3 = "_sd3_te.npz"
 
+
 def split_train_val(
-    paths: List[str], 
+    paths: List[str],
     sizes: List[Optional[Tuple[int, int]]],
-    is_training_dataset: bool, 
-    validation_split: float, 
-    validation_seed: int | None
+    is_training_dataset: bool,
+    validation_split: float,
+    validation_seed: int | None,
 ) -> Tuple[List[str], List[Optional[Tuple[int, int]]]]:
     """
     Split the dataset into train and validation
@@ -1842,7 +1833,7 @@ def get_item_for_caching(self, bucket, bucket_batch_size, image_index):
 class DreamBoothDataset(BaseDataset):
     IMAGE_INFO_CACHE_FILE = "metadata_cache.json"
 
-    # The is_training_dataset defines the type of dataset, training or validation 
+    # The is_training_dataset defines the type of dataset, training or validation
     # if is_training_dataset is True -> training dataset
     # if is_training_dataset is False -> validation dataset
     def __init__(
@@ -1981,29 +1972,25 @@ def load_dreambooth_dir(subset: DreamBoothSubset):
                     logger.info(f"set image size from cache files: {size_set_count}/{len(img_paths)}")
 
             # We want to create a training and validation split. This should be improved in the future
-            # to allow a clearer distinction between training and validation. This can be seen as a 
+            # to allow a clearer distinction between training and validation. This can be seen as a
             # short-term solution to limit what is necessary to implement validation datasets
-            # 
+            #
             # We split the dataset for the subset based on if we are doing a validation split
-            # The self.is_training_dataset defines the type of dataset, training or validation 
+            # The self.is_training_dataset defines the type of dataset, training or validation
             # if self.is_training_dataset is True -> training dataset
             # if self.is_training_dataset is False -> validation dataset
             if self.validation_split > 0.0:
-                # For regularization images we do not want to split this dataset. 
+                # For regularization images we do not want to split this dataset.
                 if subset.is_reg is True:
                     # Skip any validation dataset for regularization images
                     if self.is_training_dataset is False:
                         img_paths = []
                         sizes = []
-                    # Otherwise the img_paths remain as original img_paths and no split 
+                    # Otherwise the img_paths remain as original img_paths and no split
                     # required for training images dataset of regularization images
                 else:
                     img_paths, sizes = split_train_val(
-                        img_paths, 
-                        sizes,
-                        self.is_training_dataset, 
-                        self.validation_split, 
-                        self.validation_seed
+                        img_paths, sizes, self.is_training_dataset, self.validation_split, self.validation_seed
                     )
 
             logger.info(f"found directory {subset.image_dir} contains {len(img_paths)} image files")
@@ -2373,7 +2360,7 @@ def __init__(
         bucket_no_upscale: bool,
         debug_dataset: bool,
         validation_split: float,
-        validation_seed: Optional[int],        
+        validation_seed: Optional[int],
     ) -> None:
         super().__init__(resolution, network_multiplier, debug_dataset)
 
@@ -2431,9 +2418,9 @@ def __init__(
         self.image_data = self.dreambooth_dataset_delegate.image_data
         self.batch_size = batch_size
         self.num_train_images = self.dreambooth_dataset_delegate.num_train_images
-        self.num_reg_images = self.dreambooth_dataset_delegate.num_reg_images        
+        self.num_reg_images = self.dreambooth_dataset_delegate.num_reg_images
         self.validation_split = validation_split
-        self.validation_seed = validation_seed 
+        self.validation_seed = validation_seed
 
         # assert all conditioning data exists
         missing_imgs = []
@@ -5944,12 +5931,17 @@ def save_sd_model_on_train_end_common(
 
 
 def get_timesteps(min_timestep: int, max_timestep: int, b_size: int, device: torch.device) -> torch.Tensor:
-    timesteps = torch.randint(min_timestep, max_timestep, (b_size,), device="cpu")
+    if min_timestep < max_timestep:
+        timesteps = torch.randint(min_timestep, max_timestep, (b_size,), device="cpu")
+    else:
+        timesteps = torch.full((b_size,), max_timestep, device="cpu")
     timesteps = timesteps.long().to(device)
     return timesteps
 
 
-def get_noise_noisy_latents_and_timesteps(args, noise_scheduler, latents: torch.FloatTensor) -> Tuple[torch.FloatTensor, torch.FloatTensor, torch.IntTensor]:
+def get_noise_noisy_latents_and_timesteps(
+    args, noise_scheduler, latents: torch.FloatTensor
+) -> Tuple[torch.FloatTensor, torch.FloatTensor, torch.IntTensor]:
     # Sample noise that we'll add to the latents
     noise = torch.randn_like(latents, device=latents.device)
     if args.noise_offset:
@@ -6441,7 +6433,7 @@ def sample_image_inference(
         wandb_tracker.log({f"sample_{i}": wandb.Image(image, caption=prompt)}, commit=False)  # positive prompt as a caption
 
 
-def init_trackers(accelerator: Accelerator, args: argparse.Namespace, default_tracker_name: str): 
+def init_trackers(accelerator: Accelerator, args: argparse.Namespace, default_tracker_name: str):
     """
     Initialize experiment trackers with tracker specific behaviors
     """
@@ -6458,13 +6450,17 @@ def init_trackers(accelerator: Accelerator, args: argparse.Namespace, default_tr
         )
 
         if "wandb" in [tracker.name for tracker in accelerator.trackers]:
-            import wandb 
+            import wandb
+
             wandb_tracker = accelerator.get_tracker("wandb", unwrap=True)
 
             # Define specific metrics to handle validation and epochs "steps"
             wandb_tracker.define_metric("epoch", hidden=True)
             wandb_tracker.define_metric("val_step", hidden=True)
 
+            wandb_tracker.define_metric("global_step", hidden=True)
+
+
 # endregion
 
 
diff --git a/sd3_train_network.py b/sd3_train_network.py
index 9438bc7bc..cdb7aa4e3 100644
--- a/sd3_train_network.py
+++ b/sd3_train_network.py
@@ -450,14 +450,19 @@ def forward(hidden_states):
                 text_encoder.to(te_weight_dtype)  # fp8
                 prepare_fp8(text_encoder, weight_dtype)
 
-    def on_step_start(self, args, accelerator, network, text_encoders, unet, batch, weight_dtype):
-        # drop cached text encoder outputs
+    def on_step_start(self, args, accelerator, network, text_encoders, unet, batch, weight_dtype, is_train=True):
+        # drop cached text encoder outputs: in validation, we drop cached outputs deterministically by fixed seed
         text_encoder_outputs_list = batch.get("text_encoder_outputs_list", None)
         if text_encoder_outputs_list is not None:
             text_encodoing_strategy: strategy_sd3.Sd3TextEncodingStrategy = strategy_base.TextEncodingStrategy.get_strategy()
             text_encoder_outputs_list = text_encodoing_strategy.drop_cached_text_encoder_outputs(*text_encoder_outputs_list)
             batch["text_encoder_outputs_list"] = text_encoder_outputs_list
 
+    def on_validation_step_end(self, args, accelerator, network, text_encoders, unet, batch, weight_dtype):
+        if self.is_swapping_blocks:
+            # prepare for next forward: because backward pass is not called, we need to prepare it here
+            accelerator.unwrap_model(unet).prepare_block_swap_before_forward()
+
     def prepare_unet_with_accelerator(
         self, args: argparse.Namespace, accelerator: Accelerator, unet: torch.nn.Module
     ) -> torch.nn.Module:
diff --git a/train_network.py b/train_network.py
index a8a23fd06..2d279b3bf 100644
--- a/train_network.py
+++ b/train_network.py
@@ -9,6 +9,7 @@
 import time
 import json
 from multiprocessing import Value
+import numpy as np
 import toml
 
 from tqdm import tqdm
@@ -100,9 +101,7 @@ def generate_step_logs(
             if (
                 args.optimizer_type.lower().endswith("ProdigyPlusScheduleFree".lower()) and optimizer is not None
             ):  # tracking d*lr value of unet.
-                logs["lr/d*lr"] = (
-                    optimizer.param_groups[0]["d"] * optimizer.param_groups[0]["lr"]
-                )
+                logs["lr/d*lr"] = optimizer.param_groups[0]["d"] * optimizer.param_groups[0]["lr"]
         else:
             idx = 0
             if not args.network_train_unet_only:
@@ -115,16 +114,56 @@ def generate_step_logs(
                     logs[f"lr/d*lr/group{i}"] = (
                         lr_scheduler.optimizers[-1].param_groups[i]["d"] * lr_scheduler.optimizers[-1].param_groups[i]["lr"]
                     )
-                if (
-                    args.optimizer_type.lower().endswith("ProdigyPlusScheduleFree".lower()) and optimizer is not None
-                ):
-                    logs[f"lr/d*lr/group{i}"] = (
-                        optimizer.param_groups[i]["d"] * optimizer.param_groups[i]["lr"]
-                    )
+                if args.optimizer_type.lower().endswith("ProdigyPlusScheduleFree".lower()) and optimizer is not None:
+                    logs[f"lr/d*lr/group{i}"] = optimizer.param_groups[i]["d"] * optimizer.param_groups[i]["lr"]
 
         return logs
 
-    def assert_extra_args(self, args, train_dataset_group: Union[train_util.DatasetGroup, train_util.MinimalDataset], val_dataset_group: Optional[train_util.DatasetGroup]):
+    def step_logging(self, accelerator: Accelerator, logs: dict, global_step: int, epoch: int):
+        self.accelerator_logging(accelerator, logs, global_step, global_step, epoch)
+
+    def epoch_logging(self, accelerator: Accelerator, logs: dict, global_step: int, epoch: int):
+        self.accelerator_logging(accelerator, logs, epoch, global_step, epoch)
+
+    def val_logging(self, accelerator: Accelerator, logs: dict, global_step: int, epoch: int, val_step: int):
+        self.accelerator_logging(accelerator, logs, global_step + val_step, global_step, epoch, val_step)
+
+    def accelerator_logging(
+        self, accelerator: Accelerator, logs: dict, step_value: int, global_step: int, epoch: int, val_step: Optional[int] = None
+    ):
+        """
+        step_value is for tensorboard, other values are for wandb
+        """
+        tensorboard_tracker = None
+        wandb_tracker = None
+        other_trackers = []
+        for tracker in accelerator.trackers:
+            if tracker.name == "tensorboard":
+                tensorboard_tracker = accelerator.get_tracker("tensorboard")
+            elif tracker.name == "wandb":
+                wandb_tracker = accelerator.get_tracker("wandb")
+            else:
+                other_trackers.append(accelerator.get_tracker(tracker.name))
+
+        if tensorboard_tracker is not None:
+            tensorboard_tracker.log(logs, step=step_value)
+
+        if wandb_tracker is not None:
+            logs["global_step"] = global_step
+            logs["epoch"] = epoch
+            if val_step is not None:
+                logs["val_step"] = val_step
+            wandb_tracker.log(logs)
+
+        for tracker in other_trackers:
+            tracker.log(logs, step=step_value)
+
+    def assert_extra_args(
+        self,
+        args,
+        train_dataset_group: Union[train_util.DatasetGroup, train_util.MinimalDataset],
+        val_dataset_group: Optional[train_util.DatasetGroup],
+    ):
         train_dataset_group.verify_bucket_reso_steps(64)
         if val_dataset_group is not None:
             val_dataset_group.verify_bucket_reso_steps(64)
@@ -219,7 +258,7 @@ def get_noise_pred_and_target(
         network,
         weight_dtype,
         train_unet,
-        is_train=True
+        is_train=True,
     ):
         # Sample noise, sample a random timestep for each image, and add noise to the latents,
         # with noise offset and/or multires noise if specified
@@ -309,28 +348,31 @@ def prepare_unet_with_accelerator(
     ) -> torch.nn.Module:
         return accelerator.prepare(unet)
 
-    def on_step_start(self, args, accelerator, network, text_encoders, unet, batch, weight_dtype):
+    def on_step_start(self, args, accelerator, network, text_encoders, unet, batch, weight_dtype, is_train: bool = True):
+        pass
+
+    def on_validation_step_end(self, args, accelerator, network, text_encoders, unet, batch, weight_dtype):
         pass
 
     # endregion
 
     def process_batch(
-        self, 
-        batch, 
-        text_encoders, 
-        unet, 
-        network, 
-        vae, 
-        noise_scheduler, 
-        vae_dtype, 
-        weight_dtype, 
-        accelerator, 
-        args, 
-        text_encoding_strategy: strategy_base.TextEncodingStrategy, 
-        tokenize_strategy: strategy_base.TokenizeStrategy, 
-        is_train=True, 
-        train_text_encoder=True, 
-        train_unet=True
+        self,
+        batch,
+        text_encoders,
+        unet,
+        network,
+        vae,
+        noise_scheduler,
+        vae_dtype,
+        weight_dtype,
+        accelerator,
+        args,
+        text_encoding_strategy: strategy_base.TextEncodingStrategy,
+        tokenize_strategy: strategy_base.TokenizeStrategy,
+        is_train=True,
+        train_text_encoder=True,
+        train_unet=True,
     ) -> torch.Tensor:
         """
         Process a batch for the network
@@ -397,7 +439,7 @@ def process_batch(
             network,
             weight_dtype,
             train_unet,
-            is_train=is_train
+            is_train=is_train,
         )
 
         huber_c = train_util.get_huber_threshold_if_needed(args, timesteps, noise_scheduler)
@@ -484,7 +526,7 @@ def train(self, args):
         else:
             # use arbitrary dataset class
             train_dataset_group = train_util.load_arbitrary_dataset(args)
-            val_dataset_group = None # placeholder until validation dataset supported for arbitrary
+            val_dataset_group = None  # placeholder until validation dataset supported for arbitrary
 
         current_epoch = Value("i", 0)
         current_step = Value("i", 0)
@@ -701,7 +743,7 @@ def train(self, args):
             num_workers=n_workers,
             persistent_workers=args.persistent_data_loader_workers,
         )
-        
+
         val_dataloader = torch.utils.data.DataLoader(
             val_dataset_group if val_dataset_group is not None else [],
             shuffle=False,
@@ -900,7 +942,9 @@ def load_model_hook(models, input_dir):
 
         accelerator.print("running training / 学習開始")
         accelerator.print(f"  num train images * repeats / 学習画像の数×繰り返し回数: {train_dataset_group.num_train_images}")
-        accelerator.print(f"  num validation images * repeats / 学習画像の数×繰り返し回数: {val_dataset_group.num_train_images if val_dataset_group is not None else 0}")
+        accelerator.print(
+            f"  num validation images * repeats / 学習画像の数×繰り返し回数: {val_dataset_group.num_train_images if val_dataset_group is not None else 0}"
+        )
         accelerator.print(f"  num reg images / 正則化画像の数: {train_dataset_group.num_reg_images}")
         accelerator.print(f"  num batches per epoch / 1epochのバッチ数: {len(train_dataloader)}")
         accelerator.print(f"  num epochs / epoch数: {num_train_epochs}")
@@ -968,11 +1012,11 @@ def load_model_hook(models, input_dir):
             "ss_huber_c": args.huber_c,
             "ss_fp8_base": bool(args.fp8_base),
             "ss_fp8_base_unet": bool(args.fp8_base_unet),
-            "ss_validation_seed": args.validation_seed, 
-            "ss_validation_split": args.validation_split, 
-            "ss_max_validation_steps": args.max_validation_steps, 
-            "ss_validate_every_n_epochs": args.validate_every_n_epochs, 
-            "ss_validate_every_n_steps": args.validate_every_n_steps, 
+            "ss_validation_seed": args.validation_seed,
+            "ss_validation_split": args.validation_split,
+            "ss_max_validation_steps": args.max_validation_steps,
+            "ss_validate_every_n_epochs": args.validate_every_n_epochs,
+            "ss_validate_every_n_steps": args.validate_every_n_steps,
         }
 
         self.update_metadata(metadata, args)  # architecture specific metadata
@@ -1243,12 +1287,6 @@ def remove_model(old_ckpt_name):
             # log empty object to commit the sample images to wandb
             accelerator.log({}, step=0)
 
-        validation_steps = (
-            min(args.max_validation_steps, len(val_dataloader)) 
-            if args.max_validation_steps is not None 
-            else len(val_dataloader)
-        )
-
         # training loop
         if initial_step > 0:  # only if skip_until_initial_step is specified
             for skip_epoch in range(epoch_to_start):  # skip epochs
@@ -1271,13 +1309,53 @@ def remove_model(old_ckpt_name):
             range(args.max_train_steps - initial_step), smoothing=0, disable=not accelerator.is_local_main_process, desc="steps"
         )
 
+        validation_steps = (
+            min(args.max_validation_steps, len(val_dataloader)) if args.max_validation_steps is not None else len(val_dataloader)
+        )
+        NUM_VALIDATION_TIMESTEPS = 4  # 200, 400, 600, 800 TODO make this configurable
+        min_timestep = 0 if args.min_timestep is None else args.min_timestep
+        max_timestep = noise_scheduler.num_train_timesteps if args.max_timestep is None else args.max_timestep
+        validation_timesteps = np.linspace(min_timestep, max_timestep, (NUM_VALIDATION_TIMESTEPS + 2), dtype=int)[1:-1]
+        validation_total_steps = validation_steps * len(validation_timesteps)
+        original_args_min_timestep = args.min_timestep
+        original_args_max_timestep = args.max_timestep
+
+        def switch_rng_state(seed: int) -> tuple[torch.ByteTensor, Optional[torch.ByteTensor], tuple]:
+            cpu_rng_state = torch.get_rng_state()
+            if accelerator.device.type == "cuda":
+                gpu_rng_state = torch.cuda.get_rng_state()
+            elif accelerator.device.type == "xpu":
+                gpu_rng_state = torch.xpu.get_rng_state()
+            elif accelerator.device.type == "mps":
+                gpu_rng_state = torch.cuda.get_rng_state()
+            else:
+                gpu_rng_state = None
+            python_rng_state = random.getstate()
+
+            torch.manual_seed(seed)
+            random.seed(seed)
+
+            return (cpu_rng_state, gpu_rng_state, python_rng_state)
+
+        def restore_rng_state(rng_states: tuple[torch.ByteTensor, Optional[torch.ByteTensor], tuple]):
+            cpu_rng_state, gpu_rng_state, python_rng_state = rng_states
+            torch.set_rng_state(cpu_rng_state)
+            if gpu_rng_state is not None:
+                if accelerator.device.type == "cuda":
+                    torch.cuda.set_rng_state(gpu_rng_state)
+                elif accelerator.device.type == "xpu":
+                    torch.xpu.set_rng_state(gpu_rng_state)
+                elif accelerator.device.type == "mps":
+                    torch.cuda.set_rng_state(gpu_rng_state)
+            random.setstate(python_rng_state)
+
         for epoch in range(epoch_to_start, num_train_epochs):
             accelerator.print(f"\nepoch {epoch+1}/{num_train_epochs}\n")
             current_epoch.value = epoch + 1
 
             metadata["ss_epoch"] = str(epoch + 1)
 
-            accelerator.unwrap_model(network).on_epoch_start(text_encoder, unet)
+            accelerator.unwrap_model(network).on_epoch_start(text_encoder, unet)  # network.train() is called here
 
             # TRAINING
             skipped_dataloader = None
@@ -1294,25 +1372,25 @@ def remove_model(old_ckpt_name):
                 with accelerator.accumulate(training_model):
                     on_step_start_for_network(text_encoder, unet)
 
-                    # temporary, for batch processing
-                    self.on_step_start(args, accelerator, network, text_encoders, unet, batch, weight_dtype)
+                    # preprocess batch for each model
+                    self.on_step_start(args, accelerator, network, text_encoders, unet, batch, weight_dtype, is_train=True)
 
                     loss = self.process_batch(
-                        batch, 
-                        text_encoders, 
-                        unet, 
-                        network, 
-                        vae, 
-                        noise_scheduler, 
-                        vae_dtype, 
-                        weight_dtype, 
-                        accelerator, 
-                        args, 
-                        text_encoding_strategy, 
-                        tokenize_strategy, 
-                        is_train=True, 
-                        train_text_encoder=train_text_encoder, 
-                        train_unet=train_unet
+                        batch,
+                        text_encoders,
+                        unet,
+                        network,
+                        vae,
+                        noise_scheduler,
+                        vae_dtype,
+                        weight_dtype,
+                        accelerator,
+                        args,
+                        text_encoding_strategy,
+                        tokenize_strategy,
+                        is_train=True,
+                        train_text_encoder=train_text_encoder,
+                        train_unet=train_unet,
                     )
 
                     accelerator.backward(loss)
@@ -1369,148 +1447,167 @@ def remove_model(old_ckpt_name):
                 if args.scale_weight_norms:
                     progress_bar.set_postfix(**{**max_mean_logs, **logs})
 
-
                 if is_tracking:
                     logs = self.generate_step_logs(
-                        args, 
-                        current_loss, 
-                        avr_loss, 
-                        lr_scheduler, 
-                        lr_descriptions, 
-                        optimizer, 
-                        keys_scaled, 
-                        mean_norm, 
-                        maximum_norm
+                        args, current_loss, avr_loss, lr_scheduler, lr_descriptions, optimizer, keys_scaled, mean_norm, maximum_norm
                     )
-                    accelerator.log(logs, step=global_step)
+                    self.step_logging(accelerator, logs, global_step, epoch + 1)
 
-                # VALIDATION PER STEP
-                should_validate_step = (
-                    args.validate_every_n_steps is not None 
-                    and global_step != 0 # Skip first step
-                    and global_step % args.validate_every_n_steps == 0
-                )
+                # VALIDATION PER STEP: global_step is already incremented
+                # for example, if validate_every_n_steps=100, validate at step 100, 200, 300, ...
+                should_validate_step = args.validate_every_n_steps is not None and global_step % args.validate_every_n_steps == 0
                 if accelerator.sync_gradients and validation_steps > 0 and should_validate_step:
+                    optimizer_eval_fn()
+                    accelerator.unwrap_model(network).eval()
+                    rng_states = switch_rng_state(args.validation_seed if args.validation_seed is not None else args.seed)
+
                     val_progress_bar = tqdm(
-                        range(validation_steps), smoothing=0, 
-                        disable=not accelerator.is_local_main_process, 
-                        desc="validation steps"
+                        range(validation_total_steps),
+                        smoothing=0,
+                        disable=not accelerator.is_local_main_process,
+                        desc="validation steps",
                     )
+                    val_timesteps_step = 0
                     for val_step, batch in enumerate(val_dataloader):
                         if val_step >= validation_steps:
                             break
 
-                        # temporary, for batch processing
-                        self.on_step_start(args, accelerator, network, text_encoders, unet, batch, weight_dtype)
-
-                        loss = self.process_batch(
-                            batch, 
-                            text_encoders, 
-                            unet, 
-                            network, 
-                            vae, 
-                            noise_scheduler, 
-                            vae_dtype, 
-                            weight_dtype, 
-                            accelerator, 
-                            args, 
-                            text_encoding_strategy, 
-                            tokenize_strategy, 
-                            is_train=False,
-                            train_text_encoder=False, 
-                            train_unet=False
-                        )
-
-                        current_loss = loss.detach().item()
-                        val_step_loss_recorder.add(epoch=epoch, step=val_step, loss=current_loss)
-                        val_progress_bar.update(1)
-                        val_progress_bar.set_postfix({ "val_avg_loss": val_step_loss_recorder.moving_average })
-
-                        if is_tracking:
-                            logs = {
-                                "loss/validation/step_current": current_loss,
-                                "val_step": (epoch * validation_steps) + val_step,
-                            }
-                            accelerator.log(logs, step=global_step)
+                        for timestep in validation_timesteps:
+                            self.on_step_start(args, accelerator, network, text_encoders, unet, batch, weight_dtype, is_train=False)
+
+                            args.min_timestep = args.max_timestep = timestep  # dirty hack to change timestep
+
+                            loss = self.process_batch(
+                                batch,
+                                text_encoders,
+                                unet,
+                                network,
+                                vae,
+                                noise_scheduler,
+                                vae_dtype,
+                                weight_dtype,
+                                accelerator,
+                                args,
+                                text_encoding_strategy,
+                                tokenize_strategy,
+                                is_train=False,
+                                train_text_encoder=train_text_encoder,  # this is needed for validation because Text Encoders must be called if train_text_encoder is True
+                                train_unet=train_unet,
+                            )
+
+                            current_loss = loss.detach().item()
+                            val_step_loss_recorder.add(epoch=epoch, step=val_timesteps_step, loss=current_loss)
+                            val_progress_bar.update(1)
+                            val_progress_bar.set_postfix(
+                                {"val_avg_loss": val_step_loss_recorder.moving_average, "timestep": timestep}
+                            )
+
+                            # if is_tracking:
+                            #     logs = {f"loss/validation/step_current_{timestep}": current_loss}
+                            #     self.val_logging(accelerator, logs, global_step, epoch + 1, val_step)
+
+                            self.on_validation_step_end(args, accelerator, network, text_encoders, unet, batch, weight_dtype)
+                            val_timesteps_step += 1
 
                     if is_tracking:
                         loss_validation_divergence = val_step_loss_recorder.moving_average - loss_recorder.moving_average
                         logs = {
-                            "loss/validation/step_average": val_step_loss_recorder.moving_average, 
-                            "loss/validation/step_divergence": loss_validation_divergence, 
+                            "loss/validation/step_average": val_step_loss_recorder.moving_average,
+                            "loss/validation/step_divergence": loss_validation_divergence,
                         }
-                        accelerator.log(logs, step=global_step)
-                                        
+                        self.step_logging(accelerator, logs, global_step, epoch=epoch + 1)
+
+                    restore_rng_state(rng_states)
+                    args.min_timestep = original_args_min_timestep
+                    args.max_timestep = original_args_max_timestep
+                    optimizer_train_fn()
+                    accelerator.unwrap_model(network).train()
+                    progress_bar.unpause()
+
                 if global_step >= args.max_train_steps:
                     break
 
             # EPOCH VALIDATION
             should_validate_epoch = (
-                (epoch + 1) % args.validate_every_n_epochs == 0 
-                if args.validate_every_n_epochs is not None 
-                else True
+                (epoch + 1) % args.validate_every_n_epochs == 0 if args.validate_every_n_epochs is not None else True
             )
 
             if should_validate_epoch and len(val_dataloader) > 0:
+                optimizer_eval_fn()
+                accelerator.unwrap_model(network).eval()
+                rng_states = switch_rng_state(args.validation_seed if args.validation_seed is not None else args.seed)
+
                 val_progress_bar = tqdm(
-                    range(validation_steps), smoothing=0, 
-                    disable=not accelerator.is_local_main_process, 
-                    desc="epoch validation steps"
+                    range(validation_total_steps),
+                    smoothing=0,
+                    disable=not accelerator.is_local_main_process,
+                    desc="epoch validation steps",
                 )
 
+                val_timesteps_step = 0
                 for val_step, batch in enumerate(val_dataloader):
                     if val_step >= validation_steps:
                         break
 
-                    # temporary, for batch processing
-                    self.on_step_start(args, accelerator, network, text_encoders, unet, batch, weight_dtype)
+                    for timestep in validation_timesteps:
+                        args.min_timestep = args.max_timestep = timestep
 
-                    loss = self.process_batch(
-                        batch, 
-                        text_encoders, 
-                        unet, 
-                        network, 
-                        vae, 
-                        noise_scheduler, 
-                        vae_dtype, 
-                        weight_dtype, 
-                        accelerator, 
-                        args, 
-                        text_encoding_strategy, 
-                        tokenize_strategy, 
-                        is_train=False,
-                        train_text_encoder=False, 
-                        train_unet=False
-                    )
+                        # temporary, for batch processing
+                        self.on_step_start(args, accelerator, network, text_encoders, unet, batch, weight_dtype, is_train=False)
 
-                    current_loss = loss.detach().item()
-                    val_epoch_loss_recorder.add(epoch=epoch, step=val_step, loss=current_loss)
-                    val_progress_bar.update(1)
-                    val_progress_bar.set_postfix({ "val_epoch_avg_loss": val_epoch_loss_recorder.moving_average })
+                        loss = self.process_batch(
+                            batch,
+                            text_encoders,
+                            unet,
+                            network,
+                            vae,
+                            noise_scheduler,
+                            vae_dtype,
+                            weight_dtype,
+                            accelerator,
+                            args,
+                            text_encoding_strategy,
+                            tokenize_strategy,
+                            is_train=False,
+                            train_text_encoder=train_text_encoder,
+                            train_unet=train_unet,
+                        )
 
-                    if is_tracking:
-                        logs = {
-                            "loss/validation/epoch_current": current_loss, 
-                            "epoch": epoch + 1, 
-                            "val_step": (epoch * validation_steps) + val_step
-                        }
-                        accelerator.log(logs, step=global_step)
+                        current_loss = loss.detach().item()
+                        val_epoch_loss_recorder.add(epoch=epoch, step=val_timesteps_step, loss=current_loss)
+                        val_progress_bar.update(1)
+                        val_progress_bar.set_postfix(
+                            {"val_epoch_avg_loss": val_epoch_loss_recorder.moving_average, "timestep": timestep}
+                        )
+
+                        # if is_tracking:
+                        #     logs = {f"loss/validation/epoch_current_{timestep}": current_loss}
+                        #     self.val_logging(accelerator, logs, global_step, epoch + 1, val_step)
+
+                        self.on_validation_step_end(args, accelerator, network, text_encoders, unet, batch, weight_dtype)
+                        val_timesteps_step += 1
 
                 if is_tracking:
                     avr_loss: float = val_epoch_loss_recorder.moving_average
-                    loss_validation_divergence = val_epoch_loss_recorder.moving_average - loss_recorder.moving_average 
+                    loss_validation_divergence = val_epoch_loss_recorder.moving_average - loss_recorder.moving_average
                     logs = {
-                        "loss/validation/epoch_average": avr_loss, 
-                        "loss/validation/epoch_divergence": loss_validation_divergence, 
-                        "epoch": epoch + 1
+                        "loss/validation/epoch_average": avr_loss,
+                        "loss/validation/epoch_divergence": loss_validation_divergence,
                     }
-                    accelerator.log(logs, step=global_step)
+                    self.epoch_logging(accelerator, logs, global_step, epoch + 1)
+
+                restore_rng_state(rng_states)
+                args.min_timestep = original_args_min_timestep
+                args.max_timestep = original_args_max_timestep
+                optimizer_train_fn()
+                accelerator.unwrap_model(network).train()
+                progress_bar.unpause()
 
             # END OF EPOCH
             if is_tracking:
-                logs = {"loss/epoch_average": loss_recorder.moving_average, "epoch": epoch + 1}
-                accelerator.log(logs, step=global_step)
-                    
+                logs = {"loss/epoch_average": loss_recorder.moving_average}
+                self.epoch_logging(accelerator, logs, global_step, epoch + 1)
+
             accelerator.wait_for_everyone()
 
             # 指定エポックごとにモデルを保存
@@ -1696,31 +1793,31 @@ def setup_parser() -> argparse.ArgumentParser:
         "--validation_seed",
         type=int,
         default=None,
-        help="Validation seed for shuffling validation dataset, training `--seed` used otherwise / 検証データセットをシャッフルするための検証シード、それ以外の場合はトレーニング `--seed` を使用する"
+        help="Validation seed for shuffling validation dataset, training `--seed` used otherwise / 検証データセットをシャッフルするための検証シード、それ以外の場合はトレーニング `--seed` を使用する",
     )
     parser.add_argument(
         "--validation_split",
         type=float,
         default=0.0,
-        help="Split for validation images out of the training dataset / 学習画像から検証画像に分割する割合"
+        help="Split for validation images out of the training dataset / 学習画像から検証画像に分割する割合",
     )
     parser.add_argument(
         "--validate_every_n_steps",
         type=int,
         default=None,
-        help="Run validation on validation dataset every N steps. By default, validation will only occur every epoch if a validation dataset is available / 検証データセットの検証をNステップごとに実行します。デフォルトでは、検証データセットが利用可能な場合にのみ、検証はエポックごとに実行されます"
+        help="Run validation on validation dataset every N steps. By default, validation will only occur every epoch if a validation dataset is available / 検証データセットの検証をNステップごとに実行します。デフォルトでは、検証データセットが利用可能な場合にのみ、検証はエポックごとに実行されます",
     )
     parser.add_argument(
         "--validate_every_n_epochs",
         type=int,
         default=None,
-        help="Run validation dataset every N epochs. By default, validation will run every epoch if a validation dataset is available / 検証データセットをNエポックごとに実行します。デフォルトでは、検証データセットが利用可能な場合、検証はエポックごとに実行されます"
+        help="Run validation dataset every N epochs. By default, validation will run every epoch if a validation dataset is available / 検証データセットをNエポックごとに実行します。デフォルトでは、検証データセットが利用可能な場合、検証はエポックごとに実行されます",
     )
     parser.add_argument(
         "--max_validation_steps",
         type=int,
         default=None,
-        help="Max number of validation dataset items processed. By default, validation will run the entire validation dataset / 処理される検証データセット項目の最大数。デフォルトでは、検証は検証データセット全体を実行します"
+        help="Max number of validation dataset items processed. By default, validation will run the entire validation dataset / 処理される検証データセット項目の最大数。デフォルトでは、検証は検証データセット全体を実行します",
     )
     return parser