From a546aa20b7a5256cb0cfcddff2f09c225c15c794 Mon Sep 17 00:00:00 2001
From: Andrey Kleshchev <andreykproductengine@lindenlab.com>
Date: Tue, 14 Feb 2023 22:49:50 +0200
Subject: SL-4126 Second Life messing up NVIDIA drivers

Disable NvAPI by default
---
 indra/newview/app_settings/settings.xml | 11 ++++++++
 indra/newview/llappviewerwin32.cpp      | 48 +++++++++++++++++++--------------
 2 files changed, 39 insertions(+), 20 deletions(-)

diff --git a/indra/newview/app_settings/settings.xml b/indra/newview/app_settings/settings.xml
index 3f6adfe13d..8e70dea36e 100644
--- a/indra/newview/app_settings/settings.xml
+++ b/indra/newview/app_settings/settings.xml
@@ -8341,6 +8341,17 @@
       <key>Value</key>
       <integer>1</integer>
     </map>
+    <key>NvAPISessionOverride</key>
+    <map>
+      <key>Comment</key>
+      <string>Override NvAPI driver setting for maxim performance (HACK!!!)</string>
+      <key>Persist</key>
+      <integer>1</integer>
+      <key>Type</key>
+      <string>Boolean</string>
+      <key>Value</key>
+      <integer>0</integer>
+    </map>
     <key>PurgeCacheOnNextStartup</key>
     <map>
       <key>Comment</key>
diff --git a/indra/newview/llappviewerwin32.cpp b/indra/newview/llappviewerwin32.cpp
index 0c764fe48a..b36c5a61a3 100644
--- a/indra/newview/llappviewerwin32.cpp
+++ b/indra/newview/llappviewerwin32.cpp
@@ -386,27 +386,35 @@ int APIENTRY WINMAIN(HINSTANCE hInstance,
 		LL_WARNS() << "Application init failed." << LL_ENDL;
 		return -1;
 	}
-	
-	NvAPI_Status status;
-    
-	// Initialize NVAPI
-	status = NvAPI_Initialize();
-	NvDRSSessionHandle hSession = 0;
 
-    if (status == NVAPI_OK) 
-	{
-		// Create the session handle to access driver settings
-		status = NvAPI_DRS_CreateSession(&hSession);
-		if (status != NVAPI_OK) 
-		{
-			nvapi_error(status);
-		}
-		else
-		{
-			//override driver setting as needed
-			ll_nvapi_init(hSession);
-		}
-	}
+    NvDRSSessionHandle hSession = 0;
+    // Viewer shouldn't need NvAPI and this implementation alters global
+    // settings instead of viewer-only ones (SL-4126)
+    // TODO: ideally this should be removed, but temporary disabling
+    // it with a way to turn it back on in case of issues
+    static LLCachedControl<bool> use_nv_api(gSavedSettings, "NvAPISessionOverride", false);
+    if (use_nv_api)
+    {
+        NvAPI_Status status;
+
+        // Initialize NVAPI
+        status = NvAPI_Initialize();
+
+        if (status == NVAPI_OK)
+        {
+            // Create the session handle to access driver settings
+            status = NvAPI_DRS_CreateSession(&hSession);
+            if (status != NVAPI_OK)
+            {
+                nvapi_error(status);
+            }
+            else
+            {
+                //override driver setting as needed
+                ll_nvapi_init(hSession);
+            }
+        }
+    }
 
 	// Have to wait until after logging is initialized to display LFH info
 	if (num_heaps > 0)
-- 
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