UDP Packet Register

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1

Hello,

What is the difference between the following ways of subscribing to receive a UDP Packet.

/* initialize and register pktdump to print received packets */

gnrc_netreg_entry_t server = GNRC_NETREG_ENTRY_INIT_PID(8888, sched_active_pid);

gnrc_netreg_register(GNRC_NETTYPE_UDP, &server);

vs

/* initialize and register pktdump to print received packets */

gnrc_netreg_entry_t server = GNRC_NETREG_ENTRY_INIT_PID(GNRC_NETREG_DEMUX_CTX_ALL,

sched_active_pid);

gnrc_netreg_register(GNRC_NETTYPE_UDP, &server);

I was curious because, the value of ‘Round Trip Time’ triples If I use the 2nd way (bottom one).

Thank you

Regards,

Navneet Pandey

2

Hi,

gnrc_netreg_register() registers a thread in the registry "netreg" indicating (i) the packet type (protocol) and (ii) an additional de-multiplex context [1] (for example a UDP port) it wants to receive.

An additional RTT by the factor three seems extremely huge to me. Did you measure this between boards under the same conditions, multiple times? However, I guess a certain overhead is introduced by the dispatch mechanism. Please have a more detailed look at the implementation of gnrc_netapi_dispatch() [2].

Best Peter

[1] https://riot-os.org/api/group__net__gnrc__netreg.html#ga1a6359efa13b3bfed70af55deacde7ae [2] https://github.com/RIOT-OS/RIOT/blob/master/sys/net/gnrc/netapi/gnrc_netapi.c#L94

3

Hello Peter,

Yes, the increment was huge for sure. It turns out there was some glitch in that particular experiment. That experiment was full of glitches in terms of results. I was not able to replicate that.

But, thank you. I will have a look at the mentioned links.