MPLS parsing overhead over 100 times

[gsankara]

When adding VLAN and MPLS headers to TCP/UDP packets and their respective parsing routines, I see a huge jump in the parsing time increases 100 times with MPLS. This is not seen with VLAN header packet parsing < 5 microseconds when used instead of MPLS.

Both are 4 byte headers as I know. Any reasons behind this skew ?

transition select(hdr.ethernet.etherType) {
        16w0x8847: parse_mpls;
        16w0x800: parse_ipv4;
        16w0x86dd: parse_ipv6;
        16w0x8100: parse_vlan;
    default: accept;
}