RmsNorm kernel for metal. (#1895)

* RmsNorm kernel for metal.

* Wrapper for the metal kernel.

* Get the ops to actually work.

* Fix, get the tests to pass.

candle-metal-kernels/src/lib.rs

@@ -750,6 +750,64 @@ pub fn call_last_softmax(
     Ok(())
 }
 
+#[allow(clippy::too_many_arguments)]
+pub fn call_rms_norm(
+    device: &Device,
+    command_buffer: &CommandBufferRef,
+    kernels: &Kernels,
+    kernel_name: &'static str,
+    length: usize,
+    elements_to_sum: usize,
+    eps: f32,
+    input: &Buffer,
+    input_offset: usize,
+    alpha: &Buffer,
+    alpha_offset: usize,
+    output: &Buffer,
+) -> Result<(), MetalKernelError> {
+    let pipeline = kernels.load_pipeline(device, Source::Reduce, kernel_name)?;
+    let encoder = command_buffer.new_compute_command_encoder();
+    encoder.set_compute_pipeline_state(&pipeline);
+
+    set_params!(
+        encoder,
+        (
+            length,
+            elements_to_sum,
+            (input, input_offset),
+            output,
+            (alpha, alpha_offset),
+            eps
+        )
+    );
+
+    let out_length = length / elements_to_sum;
+
+    let thread_group_count = MTLSize {
+        width: out_length as u64,
+        height: 1,
+        depth: 1,
+    };
+
+    let width = std::cmp::min(
+        pipeline.max_total_threads_per_threadgroup(),
+        elements_to_sum as u64,
+    )
+    .next_power_of_two();
+
+    let thread_group_size = MTLSize {
+        width,
+        height: 1,
+        depth: 1,
+    };
+
+    encoder.use_resource(input, metal::MTLResourceUsage::Read);
+    encoder.use_resource(output, metal::MTLResourceUsage::Write);
+    encoder.dispatch_thread_groups(thread_group_count, thread_group_size);
+    encoder.end_encoding();
+    Ok(())
+}
+
 #[allow(clippy::too_many_arguments)]
 pub fn call_affine(
     device: &Device,