Date: Sun, 15 Apr 2012 05:11:24 +1000 From: Jason Leschnik <leschnik@gmail.com> To: Yuri <yuri@rawbw.com> Cc: freebsd-net@freebsd.org Subject: Re: Why host transmit rate on 1Gb ethernet is only ~750Mbps ? Message-ID: <CAN1XHtdfj%2BfTXKEngvT1BwRpMW29TEfQqy2XbSrdCvV_v_HHpw@mail.gmail.com> In-Reply-To: <4F89C005.2020304@rawbw.com> References: <4F89C005.2020304@rawbw.com>
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I would first start by doing a point-to-point link between your two
end nodes to rule out your network gear as being the problem
On Sun, Apr 15, 2012 at 4:20 AM, Yuri <yuri@rawbw.com> wrote:
> I am running some tests with gigabit switch between two 9.0 hosts using
> iperf.
> The best UDP transmit rate I am getting is 753 Mbits/sec with ~3-6% packe=
t
> loss @1500 MTU @ 2.5GHz CPU, even though command 'iperf -c X.X.X.X -u -b
> 1000m' requests the full gigabit.
>
> I am trying to understand what exactly usually limits the speed with one =
way
> ethernet traffic and also what causes the packet loss.
> Is it the host's CPU or rather the need to make ~83K system calls in orde=
r
> to send 1Gb of UDP data at 1500 MTU?
> Is it the NIC or it's driver ('re' on source and 'em' on destination in m=
y
> case)?
> Is it the router which is maybe too old? (Linksys EG008W, with tcpdump I
> made sure there is no ICMP traffic that is coming back from the router
> during the test).
>
> Why can't NIC send say 900 Mbps with MTU 1500 since the only overhead is
> ethernet+UDP headers which are ~120bytes out of 1500?
> Why packet loss occurs in such a simple network with just one switch and
> speeds of 75% of the maximum?
> How can I troubleshoot such situation and understand the reasons?
>
> Yuri
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--=20
Regards,
Jason Leschnik.
[m] 0432 35 4224
[w@] jason dot leschnik <at> ansto dot gov dot au
[U@]=A0jml974@uow.edu.au
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