test backward in test_tiny (#11697)

* test backward in test_tiny

* empty

examples/beautiful_mnist.py

@@ -29,8 +29,7 @@ if __name__ == "__main__":
     opt.zero_grad()
     samples = Tensor.randint(getenv("BS", 512), high=X_train.shape[0])
     loss = model(X_train[samples]).sparse_categorical_crossentropy(Y_train[samples]).backward()
-    opt.step()
-    return loss
+    return loss.realize(*opt.schedule_step())
 
   @TinyJit
   def get_test_acc() -> Tensor: return (model(X_test).argmax(axis=1) == Y_test).mean()*100

test/test_tiny.py

@@ -106,6 +106,24 @@ class TestTiny(unittest.TestCase):
     probs = Tensor.rand(1, 1, 28, 28).sequential(layers).tolist()
     self.assertEqual(len(probs[0]), 10)
 
+  # TODO: this is failing because of how swizzling rewrites the ShapeTracker of the final STORE
+  @unittest.skipIf(IMAGE>0 or (CI and Device.DEFAULT == "DSP"), "failing because of make things that can't be images not images")
+  def test_mnist_backward(self):
+    # NOTE: we don't have the whole model here for speed
+    layers = [
+      nn.Conv2d(1, 32, 5), Tensor.relu,
+      nn.Conv2d(32, 32, 5), Tensor.relu]
+
+    # replace random weights with ones
+    # TODO: there's a bug here where it's tying two of the biases together. we need UNIQUE const
+    #Tensor.realize(*[p.replace(Tensor.ones_like(p).contiguous()) for p in nn.state.get_parameters(layers)])
+    for p in nn.state.get_parameters(layers): p.replace(Tensor.empty(p.shape))
+
+    # realize gradients
+    for x in nn.state.get_parameters(layers): x.requires_grad_()
+    Tensor.empty(4, 1, 28, 28).sequential(layers).sum().backward()
+    Tensor.realize(*[x.grad for x in nn.state.get_parameters(layers) if x.grad is not None])
+
   # *** image ***
 
   @unittest.skipIf(Device.DEFAULT != "GPU", "image only supported on GPU")

tinygrad/tensor.py

@@ -252,7 +252,7 @@ class Tensor(MathTrait):
     # create the schedule
     schedule, var_vals = create_schedule_with_vars(sink)
     schedule = memory_planner(schedule)
-    if DEBUG >= 1 and len(schedule) >= 10: print(f"scheduled {len(schedule)} kernels in {(time.perf_counter()-st)*1000:.2f} ms")
+    if DEBUG >= 1 and len(schedule) > 1: print(f"scheduled {len(schedule)} kernels in {(time.perf_counter()-st)*1000:.2f} ms")
     return schedule, var_vals
 
   def schedule(self, *lst:Tensor) -> list[ScheduleItem]: