Shader keyword disable causes performance drop

Unity Engine
,
1

Hi,

I have an issue with a hlsl shader im running in unity. The shader is relatively complex with 10 keywords. Now I was running some performance tests on another machine with a worse gpu and I noticed a performance drop when i deactivate one of those keywords.

in hlsl

            #pragma multi_compile_local _ KEY1
            #pragma multi_compile_local _ KEY2
            #pragma multi_compile_local _ KEY3
            #pragma multi_compile_local _ KEY4
            #pragma multi_compile_local _ KEY5
            #pragma multi_compile_local _ KEY6
            #pragma multi_compile_local _ KEY7
            #pragma multi_compile_local _ KEY8
            #pragma multi_compile_local _ KEY9
            #pragma multi_compile_local _ KEY10

half4 frag(v2f i) : SV_Target
{
#ifdef KEY2
// complex calculation
#endif
// other stuff
}

in c# (runtime)

GetMaterial().DisableKeyword(keyword);

the complex calculation does not interact with any of the other stuff it just modifies a variable that gets passed through

Now this leaves me confused because in my mind the gpu should switch to a lower cost computation and perform better after disabling this keyword but it almost seems that both computations (with and without KEY2) are done.
my unity version is 2022.3.6f1

2

bump

maybe i didnt phrase it properly as a question. I’d like to know what happens when keywords get toggled in realtime. what exactly does the gpu do? Does it stop computing shader1 and start computing shader2? I just want to confirm this to move on to finding the cause somewhere else if thats the case.