Came across this on reddit for Attila. I was very skeptical, but it was definitely a noticeable performance increase in battles, so I gave it a shot in warhammer 2 as well. So obviously, follow the below directory only instead of attila go to warhammer2 folder, and then scripts.
Go to C:\Users\user\AppData\Roaming\The Creative Assembly\Attila\scripts and open preferences.script.txt. From there you have to search for number_of_threads 0 and replace that 0 with the amount of threads your CPU has. I have a Ryzen 1700 so I put in 16. If you have, say, Intel 7700, pop in 8. Ryzen 1500 and you can pop in 12 and so forthhttps://www.reddit.com/r/totalwar/comments/7c77w2/tw_attila_performance_tweaks/
Battle performance seems MUUUUCH better, like pre ME patch better on warhammer 2. What I was noticing before in both Attila and Warhammer 2 is that performance would be solid at the beginning of a battle, and then as both armies got closer to each other, the framerate would drop dramatically in to the 40's. It was far worse in Attila.
It's almost like the preference script/game doesn't recognize the CPU threads for some reason, so with 0 it defaults to a lower thread count. This is why I think the alt tabbing, task manager and changing cores thing works for some.
This does work well for all TW games, btw. I went and tried it with Attila, which I think doesn't recognize newer processors, so it defaults to a lower thread count. Just a guess. I went from 30s/40's during 20v20 active battles to low 50's. Still sucks IMO, but better than it was.
This does not solve FPS issues on the campaign map; I think those are more tied to Graphics card. On my below setup with a 1060, the framerate is low 50's at the beginning of a campaign with SSAO on around the vortex. On my other setup with a 1070, it hovers around 60-61. When the map expands out on either setup, framerates drop dramatically as the campaign progresses, around high 30's and low 40's. It's particularly bad around the wood elf area and mountain region just between the empire and orc desert area for some reason.