How to solve problem of high data rates of flow, hits switches that does not have flowrule for that flow, in openflow mininet?

Question

I am using iperf traffic generation and hard timeout as extension to simple_switch_13.py code in mininet with RYU SDN. I am using linear topology with 8 switches. I set the hard timeout to 5 seconds.

I am working with only one flow. I started the iperf traffic between two hosts(let's say h1 to h7. the terms used are same as terms used in mininet linear topology) for 10 seconds. When the flow started arp packets packets are generated in the network. After that a arp reply from h7 is sent to h1 which creates seven packet in messges from (s7, s6, ... , s1) and respective flowrule is installed in the switches and finally reaches h1. Then h1 sends tcp flow to h7 which also creates seven packet in messages from (s1, s2, ... , s7) and respective flow rule is installed in the switches and reaches h7. So far everything worked fine.

But once the timeout(5 seconds) is completed the flow rule in the switches is deleted. because flow is still in network what actually should happen is controller should send one packet-in message and buffer the rest of the packets so that when the respective flow rule is installed in flow table of the switch then the buffered packets will use the installed flow rule to pass the switch. But that is not happening. The controller is getting a lot of "packet-in" messages before the flow rule get installed into the switch(every packet that came to switch is coming to controller). What might be the reason for the lot of packet in messages. Is the buffers of the switch not working fine (but i am getting packet-in messages with some buffer_id). How to solve this issue?

This is also happening with idle-timeout and udp flow in the starting.(i.e. when h1 starts communication with h7) the switches along the path are generating lot of packet-in messages.

After doing a lot of research I understand that it is not problem with hard timeout or idle timeout. It is happening when a flow with high data rate hits the switch and switch didn't have that flow rule, then it is sending a lot of packet-in messages for the same flow. It is not queuing(or may be not storing the rest of the flow packets after sending one packet-in for that respective flow) those packets. How to solve this issue in mininet?