Everything works fine until i changed the mtu of ether1 to 1504 .
right after that all eoip tunnels on that interface suffer very bad performance which caused by fragmentation .
i did not change anything other than ether1 mtu . the mtu of eoip tunnels are 1500 same as before .

Does the mtu of eoip tunnels change when their parent physical interface mtu changes ?
if so what is the way to prevent changing eoip mtu ?

I think you forget one very fundamental problem:
Your EoIP packet is also just another IP packet for ether1, if EoIP packets are transmitted over ether1.
The EoIP packet is up to 1542 byte in size (1500 bytes eoip MTU + 42 bytes EoIP header).

If Layer 3 MTU on ether1 is 1500, then EoIP Packets will be fragmented to 1500 + 42 bytes. Which most internet connections can transport.
If Layer 3 MTU on ether1 is 1504, then EoIP Packets will be fragmented to 1504 + 38 bytes. Most Internet connections cannot transport 1504 byte packets.

So effectively you are generating a MTU Blackhole ranging from 1454 to 1500 bytes on the EoIP Interface.

Short: dont change L3 MTU values unless you know what you are doing

What is the solution if we want QinQ and EOIP on same interface ?

You do not need to change L3 MTU in order to get Q-in-Q working - unless you are using a x86 machine.
If so, use a Routerboard instead where you can set L2 MTU.

Maybe someone else can propose a workaround (e.g. you may try having vlan interface on ether1 with mtu 1500, and use it as parent interface to eoip instead of ether1)

Maybe someone else can propose a workaround

I need it

(e.g. you may try having vlan interface on ether1 with mtu 1500, and use it as parent interface to eoip instead of ether1)

I already tested it before posting here . unfortunately no success . it has same problem

So it is a x86 machine? Which network card are you using?

Intel Pro 1000

First, never change the MTU of the physical interface! Work with the L2 MTU that it supports!

If you are using EOIP to give transparency on your local network, you are suffering unnecessarily!

Study a little about MPLS and you will see that your problems will be solved very easily, and does not suffer from the overhead MPLS allows your MTU in increments thereby reducing fragmentation in your network. Look here: http://wiki.mikrotik.com/wiki/MPLS

Hugs!

First, never change the MTU of the physical interface! Work with the L2 MTU that it supports!

If you are using EOIP to give transparency on your local network, you are suffering unnecessarily!

Study a little about MPLS and you will see that your problems will be solved very easily, and does not suffer from the overhead MPLS allows your MTU in increments thereby reducing fragmentation in your network. Look here: http://wiki.mikrotik.com/wiki/MPLS

Hugs!

Thanks for suggestion .
as i said the network cards are intel so l2 mtu does not supported.
EOIP is used over internet , not local network .

EOIP is used over internet , not local network .

You are stuck with 1500 MTU so EoIP *must* fragment full-size packets. EoIP has a 42 byte overhead so you are fragmenting any packet over 1458 anyway.

If you are trying to shove a 9000byte jumbo frame down an EoIP packet you are going to process the fragment packets *7* times to fragment it into 1458 byte chunks.

Applying some math here, an rb951g can do about 81k pps, this fragmentation reduces that to 11.5k pps just by virtue of packet count

If you take the benchmark of 56.8k pps with firewall rules (estimating the fragmenting to be roughly equal to a firewall inspection) you'll be down to 8k pps. 8k packets * 1500 bytes = 11.44Mbps.

hope that math makes sense, but it's worse I think...

EoIP over WAN probably means ipsec encryption, because sending raw ethernet frames would be very insecure.

EoIP, fragmentation, and encryption, which eliminates any fast-path options, will pull you down to about 4Mbps.