Has been covered a million times but i have some up to date tips i want to share i have read alot of posts and none of the wrap it all up into one
this is for desktop users who have a Multi-core CPU and a modern Radeon card and at least 4Gbs of system RAM
THE IDEA
flightgear doesn't utilize multi core CPU's very well
enable multi-threading mode then check a CPU monitor Windows/Linux/Mac is irrelevant all of them have a System-Monitor of some sort
on my AMD quad-core cpu FG was only using 1 core heavily, now its balanced out across them and none of them ever maxes out witch causes a stutter for me
add to Advanced Properties in FGRUN /sim/rendering/multithreading-mode=DrawThreadPerContext
THE EFFECT ON PERFORMANCE
Windows users your Drivers have issues rendering text ie menus/window text/ect... this is a known issue
for Linux users You have 2 Drivers to pick from 1) the open source driver 2) the proprietary driver
generally i find both run a stock install of 3.0 pretty good but the
1)open source driver runs Hot! but faster frames
2)closed source driver has issues rendering text like its windows counterpart but runs good otherwise
and after you enable Multithreading mode the opensource driver takes a FPS hit
and the closed source driver gets a FPS gain
so regardless of Driver Windows or Linux /sim/rendering/multithreading-mode=DrawThreadPerContext
Helps alot with a Multicore-CPU that is not being utilized
gives increased stability and less lag when using systems and in game windows map and menus and when loading and unloading terrain
for opensource driver users if you can live with the FPS drop the stability benefits are still good
i have tested this with Flightgear 3.0 3.2 3.3
sorry if i ramble but i had to get that off my chest after fiddling with it for so long i hope this helps people