config: delete the redundant full stamp in initialize_model_parallel (#39202)

python/sglang/srt/runtime_context.py

@@ -164,7 +164,7 @@ def derive_parallel_widths(
 
     `world_size` is not among them: it is not a quotient, and `get_world_size()`
     answers with the live WORLD group, which stays right through an elastic
-    scale-up that a stamp taken at group build would not survive.
+    scale-up that a value fixed at group build would not survive.
     """
     return {
         "attn_dp_size": attn_dp_size,
@@ -268,7 +268,7 @@ class ParallelContext:
     def __init__(self):
         self._overrides = {}
         self._config = None  # parallel config bag, wired at publish
-        self._derived = {}  # widths stamped when the groups are built
+        self._derived = {}  # widths overridden permanently, as the groups are built
 
     def __getattr__(self, name):
         if name.startswith("_"):
@@ -291,14 +291,17 @@ class ParallelContext:
         overrides = self._overrides
         return overrides[name] if name in overrides else getter()
 
-    def stamp_derived_widths(self, **widths) -> None:
-        """Record the widths derived from the leaves, as the groups are built.
+    def override_permanently(self, **widths) -> None:
+        """Permanently correct a derived width the published bag can't answer
+        or no longer answers correctly -- not `RuntimeContext.override`,
+        because a derived width is not a resolved config leaf and this must
+        work with no config published at all (`multimodal_gen` lends a TP
+        group to `srt` layers with no `srt` config to publish against).
 
-        `initialize_model_parallel` computes the set through
-        `derive_parallel_widths` and hands it here; `initialize_dp_attention`
-        stamps `attn_dp_size` again once it knows the effective width, and
-        elastic EP restamps it where it already updates the live one. A stamped
-        width is what the readers answer with.
+        Lives beside, not inside, the `@contextmanager` `override` above -- a
+        name it cannot also have on this class -- because these are permanent
+        for the process, not scoped to a `with` block: none of the real
+        callers ever restore the value they set here.
         """
         self._derived.update(widths)
 
@@ -306,13 +309,13 @@ class ParallelContext:
         self._derived.clear()
 
     def _derived_width(self, name):
-        """A width the configuration implies: override, else stamp, else the
-        published leaf.
+        """A width the configuration implies: scoped override, else permanent
+        override, else the published leaf.
 
-        The leaf is computed at publish by `parallel_widths_of`; the stamp sits
-        above it because an elastic scale-up restamps `attn_dp_size` after
-        publish, and a scope that swaps in another TP group states the quotients
-        through `override`.
+        The leaf is computed at publish by `parallel_widths_of`; the permanent
+        override sits above it because an elastic scale-up corrects
+        `attn_dp_size` after publish, and a scope that swaps in another TP
+        group states the quotients through the scoped `override` above that.
 
         Nothing is recomputed on read, so overriding `tp_size` does not move
         `attn_tp_size`: name the width, or publish a config.
@@ -328,10 +331,10 @@ class ParallelContext:
             return getattr(config, name)
         raise RuntimeError(
             f"derived parallel width {name!r} is not available: it is computed "
-            "from the configured leaves at publish, and restamped when the "
-            "process groups are built. Nothing is published and nothing has "
-            "been stamped -- publish a parallel config, or state the width "
-            f"with get_parallel().override({name}=...)"
+            "from the configured leaves at publish, and permanently corrected "
+            "when the process groups are built. Nothing is published and "
+            "nothing has been set with override_permanently -- publish a "
+            f"parallel config, or state the width with get_parallel().override({name}=...)"
         )
 
     @contextmanager
@@ -1754,9 +1757,10 @@ def reset_context() -> None:
     """Clear the context-owned store (unit-test teardown): drop the published
     ``server_args`` and install fresh ``Flags`` and ``Resources``.
 
-    ``parallel`` holds the stamped derived widths, which go with the lifecycle
-    that stamped them: `_derived_width` prefers the stamp over the leaves, so
-    leaving one behind lets the next test read the previous topology.
+    ``parallel`` holds the permanently-overridden derived widths, which go
+    with the lifecycle that set them: `_derived_width` prefers them over the
+    published leaves, so leaving one behind lets the next test read the
+    previous topology.
     """
     _CONTEXT._server_args = None
     _CONTEXT._config_bags = None