rtnet increase default mtu

rtnet increase default mtu

[Luca Barisani]

Hi,

I'm testing xenomai 3.1.0-rc2+linux kernel 4.19 with rtnet.
The application sends udp packets between a small number of units (intel
celeron/i5), some with an e1000 and others with igb (i210), connected
to the same switch and isolated from the rest of the network.
Rtnet is loaded without tdma support, I'm using nomac and so far all is
working fine. However, I was wondering if it could be possible to increase
mtu default value of 1500 to improve bandwidth.
I could not find any mtu option within rtifconfig, so I'm asking if this
value is fixed by design, maybe to avoid ip fragmentation, or there are
some ways to change its size.

Thanks
Luca

Re: rtnet increase default mtu

[Jan Kiszka]

On 09.11.19 10:23, Luca Barisani via Xenomai wrote:
> Hi,
> 
> I'm testing xenomai 3.1.0-rc2+linux kernel 4.19 with rtnet.
> The application sends udp packets between a small number of units (intel
> celeron/i5), some with an e1000 and others with igb (i210), connected
> to the same switch and isolated from the rest of the network.
> Rtnet is loaded without tdma support, I'm using nomac and so far all is
> working fine. However, I was wondering if it could be possible to increase
> mtu default value of 1500 to improve bandwidth.
> I could not find any mtu option within rtifconfig, so I'm asking if this
> value is fixed by design, maybe to avoid ip fragmentation, or there are
> some ways to change its size.

MTU modification is not available. That used to be by design as RTnet 
builds upon statically sized (and allocated) buffers. Modern NICs could 
likely spread jumbo frames over multiple buffers, so it should work - 
but the infrastructure is missing.

Jan

-- 
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux

Re: rtnet increase default mtu

[Luca Barisani]

Ok, thanks anyway. I thought it was possible since I found in
ipv4/ip_fragment.c some functions already implemented in that direction.

Luca

Il giorno lun 11 nov 2019 alle ore 08:00 Jan Kiszka <jan.kiszka@siemens.com>
ha scritto:

> On 09.11.19 10:23, Luca Barisani via Xenomai wrote:
> > Hi,
> >
> > I'm testing xenomai 3.1.0-rc2+linux kernel 4.19 with rtnet.
> > The application sends udp packets between a small number of units (intel
> > celeron/i5), some with an e1000 and others with igb (i210), connected
> > to the same switch and isolated from the rest of the network.
> > Rtnet is loaded without tdma support, I'm using nomac and so far all is
> > working fine. However, I was wondering if it could be possible to
> increase
> > mtu default value of 1500 to improve bandwidth.
> > I could not find any mtu option within rtifconfig, so I'm asking if this
> > value is fixed by design, maybe to avoid ip fragmentation, or there are
> > some ways to change its size.
>
> MTU modification is not available. That used to be by design as RTnet
> builds upon statically sized (and allocated) buffers. Modern NICs could
> likely spread jumbo frames over multiple buffers, so it should work -
> but the infrastructure is missing.
>
> Jan
>
> --
> Siemens AG, Corporate Technology, CT RDA IOT SES-DE
> Corporate Competence Center Embedded Linux
>