#691 Windows: generation slows when the server window is minimized (EcoQoS moves threads to E-cores) — fix included

本文

## Problem

On Windows 11 with a hybrid CPU (here an i9-13980HX, P+E cores), generation slows down (about 20%) when the server's console window is minimized. Having another window focused makes no difference. Windows power throttling (EcoQoS) treats the server and its children (`strata.exe`, `strata-vision.exe`) as background work and moves their threads to the E-cores.

## Fix

Opt the server and every contained child out of power throttling with `SetProcessInformation(ProcessPowerThrottling)`. This is done in `serve/winjob.py`, since `contain()` already handles every child process:

```diff
diff --git a/serve/winjob.py b/serve/winjob.py
index 008642a..c5db5f3 100644
--- a/serve/winjob.py
+++ b/serve/winjob.py
@@ -4,7 +4,8 @@ Closing the console window, Task Manager or a crash end the server without runni
 the vision encoder and the MCP servers kept running on their own. `contain(proc)` puts a child in a job object that
 is set to kill everything in it when its last handle closes - and the only handle is this process's, which the OS
 closes however the server ends. Processes the child starts later join the same job. The server itself stays out of
-the job, so a browser that `--open` starts is not tied to it. Elsewhere, and if the job cannot be made, a no-op.
+the job, so a browser that `--open` starts is not tied to it. Each child (and the server) is also opted out of
+Windows power throttling, see `no_throttle`. Elsewhere, and if the job cannot be made, a no-op.
 """
 from __future__ import annotations
 
@@ -57,6 +58,21 @@ if os.name == "nt":
             return None
         return job
 
+    class _PowerThrottling(ctypes.Structure):
+        _fields_ = [("Version", wintypes.ULONG), ("ControlMask", wintypes.ULONG), ("StateMask", wintypes.ULONG)]
+
+    _k32.SetProcessInformation.argtypes = (wintypes.HANDLE, ctypes.c_int, wintypes.LPVOID, wintypes.DWORD)
+
+    def no_throttle(handle) -> bool:
+        """Opt a process out of Windows power throttling (EcoQoS). Without this, Windows 11 treats a process whose
+        console window is minimized as background and, on hybrid CPUs, moves its threads to the E-cores:
+        generation slowed down by about 20% while the server window was minimized."""
+        info = _PowerThrottling(1, 0x1 | 0x4, 0)    # control EXECUTION_SPEED and IGNORE_TIMER_RESOLUTION, both off
+        return bool(_k32.SetProcessInformation(handle, 4, ctypes.byref(info), ctypes.sizeof(info)))  # ProcessPowerThrottling
+
+    _k32.GetCurrentProcess.restype = wintypes.HANDLE
+    no_throttle(_k32.GetCurrentProcess())           # the server itself (tokenizing, streaming) too
+
 
 def contain(proc) -> bool:
     """Put a started subprocess.Popen in the kill-on-close job. True if it is in; False (harmlessly) otherwise."""
@@ -69,6 +85,7 @@ def contain(proc) -> bool:
         if not _job:
             return False
     try:
+        no_throttle(int(proc._handle))
         return bool(_k32.AssignProcessToJobObject(_job, int(proc._handle)))
     except (AttributeError, OSError, ValueError):
         return False
```

`python -m unittest serve.test_winjob` still passes.

## Measured with the patch

Setup: RTX 4090 Laptop 16 GB, i9-13980HX, 96 GB RAM, Qwen3.8-Flash-Next IQ3_S, AC power, Balanced plan. Same prompt at temperature 0 with 400 max tokens, 3 rounds each:

| Server window | Median tok/s | Runs |
|---|---|---|
| Focused | 44.3 | 42.1 / 46.8 / 44.3 |
| Another window focused | 43.0 | 43.0 / 40.4 / 44.3 |
| Minimized | 45.0 | 41.9 / 45.9 / 45.0 |

With the patch, minimizing no longer makes a difference beyond run-to-run noise. Numbers without the patch are in the comment below. Not yet tested on battery, where Windows throttles more aggressively.