Hi,
I'm playing around with a simulation, in which many thousands of IP
addresses (on interface aliases) are used to send/receive TCP/UDP
packets. I noticed that the time of send/sendto increased linearly
with the number of file descriptors, and I found it rather strange. I
searched for some related topics, but I couldn't find any (I might
have chosen the wrong keywords).
Though, I'm a real kernelnewbie, I made up my mind to follow what is
happening in the deep. I used the printk and do_gettimeofday
functions to print timestamps at certain points of the execution path
to identify the bottleneck. Each socket is bound to a dedicated IP
address and each socket is using the very same port number, with the
help of SO_REUSEADDR socket option. I use the 2.16.19-r5
gentoo-sources on my Compaq Evo N1020v laptop. So far, I could get to
the following point:
Function/macro: Location:
sys_send net/socket.c
sys_sendto net/socket.c
sock_sendmsg net/socket.c
__sock_sendmsg net/socket.c
(*socket_sendmsg)=inet_sendmsg net/ipv4/af_inet.c
(*sendmsg)=udp_sendmsg net/ipv4/udp.c
udp_push_pending_frames net/ipv4/udp.c
ip_push_pending_frames net/ipv4/ip_output.c
NF_HOOK include/linux/netfilter.h
ip_output net/ipv4/ip_output.c
ip_finish_output net/ipv4/ip_output.c
ip_finish_output2 net/ipv4/ip_output.c
dst->heighbour->output=dev_queue_xmit net/core/dev.c
rcu_read_unlock_bh include/linux/rcupdate.c
local_bh_enable kernel/softirq.c
At this point, I felt really helpless, and I don't even know if I'm
at the right track in this investigation. So, can someone please
help me with advice or links pointing to the info I need? Let me know
if you need any further input.
I expect that sending a packet should not depend on the number of
file descriptors (sockets), it should be a more or less constant time
operation. Can you confirm this, or is there something in the kernel
or elsewhere preventing it?
Any hints are welcome. Thanks a lot!
/Zacco
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