netdev - Re: Netperf UDP issue with connected sockets

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Message-ID: <alpine.LFD.2.11.1611180145580.2135@ja.home.ssi.bg>
Date:   Fri, 18 Nov 2016 02:37:09 +0200 (EET)
From:   Julian Anastasov <ja@....bg>
To:     Rick Jones <rick.jones2@....com>
cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        netdev@...r.kernel.org, Saeed Mahameed <saeedm@...lanox.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: Netperf UDP issue with connected sockets


	Hello,

On Thu, 17 Nov 2016, Rick Jones wrote:

> raj@...dy:~/netperf2_trunk$ strace -v -o /tmp/netperf.strace src/netperf -F
> src/nettest_omni.c -t UDP_STREAM -l 1 -- -m 1472
> 
> ...
> 
> socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 4
> getsockopt(4, SOL_SOCKET, SO_SNDBUF, [212992], [4]) = 0
> getsockopt(4, SOL_SOCKET, SO_RCVBUF, [212992], [4]) = 0
> setsockopt(4, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> bind(4, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("0.0.0.0")},
> 16) = 0
> setsockopt(4, SOL_SOCKET, SO_DONTROUTE, [1], 4) = 0

	connected socket can benefit from dst cached in socket
but not if SO_DONTROUTE is set. If we do not want to send packets
via gateway this -l 1 should help but I don't see IP_TTL setsockopt
in your first example with connect() to 127.0.0.1.

	Also, may be there can be another default, if -l is used to
specify TTL then SO_DONTROUTE should not be set. I.e. we should
avoid SO_DONTROUTE, if possible.

Regards

--
Julian Anastasov <ja@....bg>