On 04/24/2014 06:15 PM, ratheesh kannoth wrote:
> I did an experiment and this experiment gave me an unexpected result
> ( for me). I would like to get any clue or hint on this.
> [ ubuntu kernel version 3.11 ]
>
> i wrote an userpace program to create two tap devices( tap77 and tap88
> ) and will epoll on these fds. if a packet is received on tap77 fd,
> it will be read() and write to tap88 fd and vice versa. Basically
> this program will send pkts from tap88 to tap77 and vice versa. when
> i sent 10 icmp packets (using ping ); i got rtt min/avg/max/mdev
> =.825/1.006/2.052/.310 ms.
>
>
> I modified tun_net_xmit() function in tun.c and created another
> driver and ran the above test.
>
> tun_net_xmit() {
>
> skb_orphan(skb);
>
> if( skb->dev == tap77_dev ) skb->dev= tap88_dev
> else if (skb->dev == tap88_dev ) skb->dev = tap77_dev;
>
> skb_reset_mac_header(skb);
> skb_reset_network_header(skb);
> skb_reset_transport_header(skb);
>
> netif_rx_ni(skb);
netif_rx_ni(skb); will insert the skb into a queue. We can not make sure
when this skb is handled. So use this function is not accurate to
performance.
Best Regards!
Zhu Yanjun
> }
>
>
> i got rtt min/avg/max/mdev = .778/1.023/2.662/.549.
>
>
> With the modified driver, Although we avoided 2 packet copies and 2
> system call, it did not result in performance
> improvement ( it did decrease by a small delta ).
>
> Thanks,
> Ratheesh
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