netdev - Re: Netperf UDP issue with connected sockets

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Date:   Thu, 17 Nov 2016 16:42:29 -0800
From:   Rick Jones <rick.jones2@....com>
To:     Julian Anastasov <ja@....bg>
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

On 11/17/2016 04:37 PM, Julian Anastasov wrote:
> 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.

The global -l option specifies the duration of the test.  It doesn't 
specify the TTL of the IP datagrams being generated by the actions of 
the test.

I resisted setting SO_DONTROUTE for a number of years after the first 
instance of UDP_STREAM being used in link up/down testing took-out a 
company's network (including security camera feeds to galactic HQ) but 
at this point I'm likely to keep it in there because there ended-up 
being a second such incident.  It is set only for UDP_STREAM.  It isn't 
set for UDP_RR or TCP_*.  And for UDP_STREAM it can be overridden by the 
test-specific -R option.

happy benchmarking,

rick jones