i am just guessing...

could it be that new driver is doing some extra copy (or copies) on the
packet buffer in transmission or reception? that may be a reason for
performance impact in case of large packets...


On Tue, Mar 8, 2011 at 8:06 PM, John Pruitt <community-noreply@qnx.com>wrote:

> I am writing a new devnp network driver. When doing ping with large packets
> (ping -s 1600) I was getting messages about over-sized packets in the system
> log. I read another forum post and it suggested removing the CRC bytes. Upon
> further inspection, the device I am using does indeed include the CRC bytes
> and when they are removed (changing the packet length by subtracting 4) then
> the large packets sort of work.
>
> Before removing the CRC bytes, the ping did not work. Probably because the
> bad packets were being thrown out.
>
> Now, the packets are received and the ping technically works, but there is
> a large delay between the packets. There are 2 commands below, one with
> regular sized packets, and one with size of 1600.
>
> Any ideas as to why the times are so large with the large packets? I can do
> the same ping with large packets  from a different target to the same
> host(10.0.102.18) and the times are consistently 2-3ms instead of several
> hundred. (i.e. it is probably not the host at 10.0.102.18 that is causing
> the slowness). The target with the problem is actually faster than the
> target without the slowness. For regular size packets, it sees 0-1ms as
> shown below. The other target usually sees 2-3ms regardless of packet size.
>
> # ping -c 3 10.0.102.18; ping -s 1600 -c 3 10.0.102.18
> PING 10.0.102.18 (10.0.102.18): 56 data bytes
> 64 bytes from 10.0.102.18: icmp_seq=0 ttl=128 time=1 ms
> 64 bytes from 10.0.102.18: icmp_seq=1 ttl=128 time=0 ms
> 64 bytes from 10.0.102.18: icmp_seq=2 ttl=128 time=0 ms
>
> ----10.0.102.18 PING Statistics----
> 3 packets transmitted, 3 packets received, 0% packet loss
> round-trip min/avg/max = 0/0/1 ms   variance = 0 ms^2
> PING 10.0.102.18 (10.0.102.18): 1600 data bytes
> 1608 bytes from 10.0.102.18: icmp_seq=0 ttl=128 time=758 ms
> 1608 bytes from 10.0.102.18: icmp_seq=1 ttl=128 time=258 ms
> 1608 bytes from 10.0.102.18: icmp_seq=2 ttl=128 time=787 ms
>
> ----10.0.102.18 PING Statistics----
> 3 packets transmitted, 3 packets received, 0% packet loss
> round-trip min/avg/max = 258/601/787 ms   variance = 88447 ms^2
>
>
>
> _______________________________________________
>
> Networking Drivers
> http://community.qnx.com/sf/go/post83822
>
>