[ssl/bestrq] happy ending---stable training (#2614)

* [ssl/bestrq] happy ending

* fix multibook loss

wenet/ssl/bestrq/bestrq_model.py

@@ -3,7 +3,7 @@
 import torch
 
 from wenet.ssl.bestrq.mask import compute_mask_indices_v2
-from wenet.utils.mask import make_pad_mask
+from wenet.utils.mask import make_non_pad_mask, make_pad_mask
 from wenet.transformer.attention import RelPositionMultiHeadedAttention
 from wenet.transformer.encoder_layer import ConformerEncoderLayer
 
@@ -96,12 +96,7 @@ def __init__(
         # stack input: eg: fbank
         self.stack_frames = self.encoder.embed.right_context + 1
         self.stride = self.encoder.embed.subsampling_rate
-        input_dim = num_mel_bins * self.stack_frames
-
-        # norm input
-        self.norm = torch.nn.LayerNorm(
-            input_dim, eps=norm_epsilon, elementwise_affine=False
-        ) if self.stack_frames > 1 else torch.nn.Identity()
+        input_dim = num_mel_bins * self.stride
 
         # random projectoin
         self.projection = torch.nn.parameter.Parameter(
@@ -177,11 +172,12 @@ def forward(
         xs, code_ids_mask = self._apply_mask_signal(xs, xs_lens)
 
         # 2.0 stack fbank
-        unmasked_xs = self._stack_features(input)
+        unmasked_xs = self._stack_features(input, xs_lens)
         masked_xs = xs
 
         # 2.1 get nearest embedding
         target_ids = self._nearest_embedding_idx(unmasked_xs)
+        target_ids = target_ids[:, :code_ids_mask.size(1), :]
 
         # 3 forward xxx-formaer block and its subsampling layer
         out, out_mask = self.encoder(masked_xs, xs_lens)
@@ -258,30 +254,40 @@ def _apply_mask_signal(
         xs = torch.where(masks_expand, mask_emb, input)
         return xs, subsampling_mask
 
-    def _stack_features(self, input: torch.Tensor) -> torch.Tensor:
+    def _stack_features(self, input: torch.Tensor,
+                        input_lens: torch.Tensor) -> torch.Tensor:
 
-        stack_input = input.unfold(1, size=self.stack_frames, step=self.stride)
+        stack_input = input.unfold(1, size=self.stride, step=self.stride)
         stack_input = stack_input.transpose(-1, -2)
         b, n, f, d = stack_input.size()
         stack_input = stack_input.reshape(b, n, f * d)
 
-        return stack_input
+        # NOTE(Mddct): important!!!
+        # norm stack features
+        mask = make_non_pad_mask(input_lens)
+        stack_mask = mask.unfold(1, size=self.stride, step=self.stride)
+        stack_mask, _ = torch.min(stack_mask, dim=-1)
+
+        stack_input = stack_input * stack_mask.unsqueeze(2)
+        mean = stack_input.sum(1, keepdim=True) / stack_mask.sum(
+            dim=1, keepdim=True).unsqueeze(1)
+        std = torch.sqrt(((stack_input - mean)**2).sum(dim=1, keepdim=True) /
+                         stack_mask.sum(dim=1, keepdim=True).unsqueeze(1))
+        norm_stack_input = (stack_input - mean) / (std + 1e-5)
+        return norm_stack_input
 
     def _compute_loss(self, input: torch.Tensor, target: torch.Tensor,
                       mask: torch.Tensor) -> torch.Tensor:
-        log_probs = torch.log_softmax(input, dim=-1).transpose(
-            1, 2)  # [B, T', num_codebooks, num_embeddings]
-
-        per_example_n_loss = -log_probs.gather(3, target.unsqueeze(3)).squeeze(
-            3)  # [B, T', num_codebooks]
-
-        numerator = torch.sum(per_example_n_loss * mask.unsqueeze(2))
-        denominator = torch.sum(mask) + 1e-5
-        loss = numerator / (denominator * self.num_codebooks)
+        logits = input.transpose(1, 2).contiguous().view(-1, input.size(-1))
+        loss = torch.nn.functional.cross_entropy(
+            logits,
+            target.contiguous().view(-1),
+            reduction='none',
+        )
+        loss = (loss * mask.view(-1)).sum() / mask.sum()
         return loss
 
     def _nearest_embedding_idx(self, xs: torch.Tensor) -> torch.Tensor:
-        xs = self.norm(xs)
         xs = torch.matmul(xs, self.projection.to(xs.device))
         xs = xs / (xs.norm(dim=-1, p=2, keepdim=True) + 1e-8)
         codebooks = self.embeddings