[systemd-devel] networkd: Is auto-negotiation turned off when specifying parameters in a link file?

[Lennart Poettering]

On Mon, 06.04.15 22:16, Paul Menzel (paulepanter at users.sourceforge.net) wrote:

> Am Freitag, den 03.04.2015, 16:47 +0200 schrieb Lennart Poettering:
> > On Thu, 02.04.15 13:11, Paul Menzel wrote:
> 
> > > some network cards with certain cables and devices take up to five
> > > seconds so that the link is up [1].
> > > 
> > >         $ sudo journalctl -u systemd-networkd
> > >         -- Logs begin at Fr 2015-03-20 17:39:31 CET, end at So 2015-03-22 08:39:39 CET. --
> > >         Mär 20 17:39:31 myhostname systemd-networkd[245]: lo              : gained carrier
> > >         Mär 20 17:39:31 myhostname systemd-networkd[245]: eth0            : link configured
> > >         Mär 20 17:39:34 myhostname systemd-networkd[245]: eth0            : gained carrier
> > > 
> > > This is annoying if the system is up, but you cannot log into a server
> > > because the NIC is so slow configuring the link.
> > > 
> > > The Linux kernel module developers from the e1000-devel mailing list
> > > suggested the following [2]:
> > > 
> > > > Both sides either need to be forced or both sides need to be auto-neg.
> > > > Otherwise the auto-negotiation process will usually detect link (the
> > > > physical signal) but fail to find duplex (since one side is not
> > > > talking) and default to the lowest common denominator, e.g. half
> > > > duplex.  So, you could try forcing speed, it may look right on your
> > > > end but if you have no visibility to the other end it could be running
> > > > at half duplex.
> > > >
> > > > You may be able to speed up the auto negotiation process by
> > > > exclusively advertising 1000 Mbps Full Duplex.
> > > >
> > > > # ethtool -s ethX advertise 0x20
> > > 
> > > In the IRC channel #systemd at irc.freenode.net somebody told me to look
> > > into systemd’s network link configuration (`man systemd.link`).
> > > 
> > > Reading the manual page, it’s not clear to me, if auto-negotiation is
> > > going to be disabled, if the following is set.
> > > 
> > >         BitsPerSecond=1G
> > >         Duplex=Full
> > > 
> > > Is that equivalent to `ethtool -s ethX advertise 0x20`? If not, how
> > > could I set that up?
> > 
> > BitsPerSecond= and Duplex= are equivalent to "ethtool speed" and
> > "ethtool duplex". 
> > 
> > We currently have no setting in .link files that was equivalent to
> > "ethtool advertise". Maybe we could add that, Tom?
> > 
> > Paul, are you sure that this will really cut 5s from the configuration
> > time? Did you try this?
> 
> I am not sure and didn’t try this, as I do not know where to integrate
> that `ethtool -s eth0 advertise …` call. In udev or `systemd-networkd`?
> 
> If somebody could help me, how I can test this, I’ll report my findings
> back.

Wouldn't it suffice to unplug the ethernet cable, then use ethtool to
turn this on, then replug it, and measuring the time until networkd
notices the link beat is back?

Lennart

-- 
Lennart Poettering, Red Hat