Performance on PowerQuicc8280 linux based

[aldo lab]

I've a system Linux based on ppc8280 platform with unstable
performance from a compiling to another.
I've a board with 2 Ethernet interfaces and I inject traffic in one of
this and analyze the number of packets that I receive in the other
one.
I obtained 60000 pkt/s the first time, the second time i recompiling
the kernel just changing some died function that is not involved in
the flow of the packet.In that case I obtained 47000 pkt/s and it
seems that moving code position change the behaviour in term of cache
functionality.
Could someone help me to understand this strange situation

Regards
Aldo