Speedup ShardedSafeTensors to load Tensors with default hints (#1384)

* Speedup ShardedSafeTensors to load Tensors with default hints

* Tweaks.

---------

Co-authored-by: Laurent <laurent.mazare@gmail.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/candle-nn/src/var_builder.rs b/candle-nn/src/var_builder.rs
index cbd238dd..9d245f12 100644
--- a/candle-nn/src/var_builder.rs
+++ b/candle-nn/src/var_builder.rs
@@ -535,12 +535,18 @@ impl Backend for ShardedSafeTensors {
 
     fn get(
         &self,
-        _target_shape: Shape, // The size is not checked for ShardedTensors
+        target_shape: Shape, // The size is only checked when the world size is 1.
         path: &str,
         h: Self::Hints,
         dtype: DType,
         dev: &Device,
     ) -> Result<Tensor> {
+        if h.world_size == 1 {
+            // There is no sharding to be applied here so we use the default backend to speed
+            // things up.
+            return SimpleBackend::get(&self.0, target_shape, path, Default::default(), dtype, dev);
+        }
+
         let Shard {
             dim,
             rank,