Index: viewer.cpp
===================================================================
--- viewer.cpp	(revision 56551)
+++ viewer.cpp	(working copy)
@@ -3522,6 +3522,69 @@
 	// here.
 	request_initial_instant_messages();
 
+
+#if LL_WINDOWS
+	//	Process affinity hack to make SL perform better on multi-core systems
+	static DWORD dwOriginalProcessAffinityMask = 0;
+	static DWORD dwCurrentAffinityMask = 0;
+	static U32 u32FrameAffinitySet = 0;
+
+	if ((u32FrameAffinitySet == 0) && (!gTeleportDisplay) && (gFrameCount >= 30))	//gStartupState == STATE_FIRST)
+	{
+		//	Observation from my Athlon 64 X2 4200+ and Intel Core 2 Duo E6600 based machines:
+		//	- launch Second Life
+		//	- connect
+		//	- observe frame rate of n FPS
+		//	- using task manager force SL to run on CPU core #0
+		//	- observe frame rate of 2*n FPS
+		//	- using task manager force SL to run on both CPU core #0 and #1
+		//	- observe frame rate of 3*n FPS
+		//
+		//	If you repeat the above experiment without connecting to SL first then once you
+		//	connect to SL your framerate will still be about 1/3 of what it should be.
+		//
+		//	So the goal here is to perform that task manager hack in code until we can find
+		//	the real problem and correct it.
+		
+		HANDLE	hProcess						= GetCurrentProcess();
+		DWORD	dwSystemAffinityMask			= 0;
+
+		if (GetProcessAffinityMask(hProcess, &dwOriginalProcessAffinityMask, &dwSystemAffinityMask) != 0)
+		{
+			//	Find the first available processor
+			for (int i = 0; i < 32; i++)
+			{
+				if ((dwOriginalProcessAffinityMask & (1 << i)) != 0)
+				{
+					dwCurrentAffinityMask = 1 << i;
+					break;
+				}
+			}
+
+			//	Tell SL to only run on that processor
+			SetProcessAffinityMask(hProcess, dwCurrentAffinityMask);
+
+			u32FrameAffinitySet = gFrameCount;
+		}
+
+		CloseHandle(hProcess);	//	Not required, but here for future compatibility since someday GetCurrentProcess() may not return a pseudo-handle
+	}
+
+	if ((dwCurrentAffinityMask != dwOriginalProcessAffinityMask) && (u32FrameAffinitySet != 0) && (gFrameCount >= u32FrameAffinitySet + 30) && (!gTeleportDisplay))	//(dwCurrentAffinityMask != dwOriginalProcessAffinityMask) && (gStartupState == STATE_STARTED))
+	{
+		HANDLE	hProcess	= GetCurrentProcess();
+
+		dwCurrentAffinityMask = dwOriginalProcessAffinityMask;
+
+		//	Now run on whatever processor(s) SL was running on
+		SetProcessAffinityMask(hProcess, dwCurrentAffinityMask);
+
+		CloseHandle(hProcess);	//	Not required, but here for future compatibility since someday GetCurrentProcess() may not return a pseudo-handle
+	}
+#endif	//	LL_WINDOWS
+
+
+
 	///////////////////////////////////
 	//
 	// Special case idle if still starting up