Revert "Revert "feat: deprecate num_replicas_per_thread, generate default value for it""

This reverts commit 6ae42edeb9.

crates/tabby/src/serve/engine.rs

@@ -5,6 +5,7 @@ use serde::Deserialize;
 use tabby_common::path::ModelDir;
 use tabby_inference::TextGeneration;
 
+use super::Device;
 use crate::fatal;
 
 pub fn create_engine(
@@ -68,13 +69,26 @@ fn create_ctranslate2_engine(
 ) -> Box<dyn TextGeneration> {
     let device = format!("{}", args.device);
     let compute_type = format!("{}", args.compute_type);
+    let num_replicas_per_device = {
+        let num_cpus = std::thread::available_parallelism()
+            .expect("Failed to read # of cpu")
+            .get();
+        if args.device == Device::Cuda {
+            // When device is cuda, set parallelism to be number of thread.
+            num_cpus
+        } else {
+            // Otherwise, adjust the number based on threads per replica.
+            // https://github.com/OpenNMT/CTranslate2/blob/master/src/utils.cc#L77
+            std::cmp::max(num_cpus / 4, 1)
+        }
+    };
     let options = CTranslate2EngineOptionsBuilder::default()
         .model_path(model_dir.ctranslate2_dir())
         .tokenizer_path(model_dir.tokenizer_file())
         .device(device)
         .model_type(metadata.auto_model.clone())
         .device_indices(args.device_indices.clone())
-        .num_replicas_per_device(args.num_replicas_per_device)
+        .num_replicas_per_device(num_replicas_per_device)
         .compute_type(compute_type)
         .build()
         .unwrap();

crates/tabby/src/serve/mod.rs

@@ -139,9 +139,9 @@ pub struct ServeArgs {
     #[clap(long, default_values_t=[0])]
     device_indices: Vec<i32>,
 
-    /// Number of replicas per device, only applicable for CPU.
-    #[clap(long, default_value_t = 1)]
-    num_replicas_per_device: usize,
+    /// DEPRECATED: Do not use.
+    #[clap(long)]
+    num_replicas_per_device: Option<usize>,
 
     /// Compute type
     #[clap(long, default_value_t=ComputeType::Auto)]
@@ -281,6 +281,10 @@ fn fallback() -> routing::MethodRouter {
 }
 
 fn valid_args(args: &ServeArgs) {
+    if args.num_replicas_per_device.is_some() {
+        warn!("num_replicas_per_device is deprecated and will be removed in future release.");
+    }
+
     if args.device == Device::Cpu && (args.device_indices.len() != 1 || args.device_indices[0] != 0)
     {
         fatal!("CPU device only supports device indices = [0]");