Why LoadAndAssign take long time when loop times increased?

[wishsym]

I have a CLS_ACT bpf progrom using loop to parse pkt, like this
for (int i = 0; i < MAX_TIMES; i++) {...}
In kernel 5.15, when I try to use LoadAndAssign, it takes more time when MAX_TIMES increased. (30s when MAX_TIMES=96)
What's worse, it loads failed when MAX_TIMES increased to 100, and only reports a single err msg: "invalidate argument"
So, can anyone tell me why it happens?

[ti-mo]

Hi, thanks for the question. Unfortunately, with the limited info you've provided, it's hard to give practical advice on how to work around this. Please include full error messages when creating issues/questions, as well as surrounding lines of code (are you using #pragma unroll?)

Generally, introducing loops into a bpf program means the verifier has more work to do, and loading the program will take longer. As you've likely noticed, this can have quadratic effects. https://docs.ebpf.io/linux/concepts/loops should be a good jumping-off point for the various looping strategies.

To rule out any issues with the library, feel free to profile the load operation and report back if something seems out of the ordinary. The vast majority of time should be spent in the PROG_LOAD syscall.