Re: Link up wait timeout [was: Bug#537271: netcfg: new version of gateway reachability patch]
On Wed, Feb 09, 2011 at 11:00:29AM +0000, Otavio Salvador wrote:
> On Wed, Feb 9, 2011 at 09:57, Matthew Palmer <mpalmer@debian.org> wrote:
> > [Taking this off-bug]
> >
> > On Wed, Feb 09, 2011 at 02:52:53AM -0500, Robert Edmonds wrote:
> >> btw, (unrelated to #537271), it seems to me that 3 seconds is a fairly
> >> short value for NETCFG_LINK_WAIT_TIME. i'm pretty sure i've seen
> >> link-up take longer than that on occasion before, depending on NIC
> >> chipset, switch, autonegotiation latency, etc.
> >
> > I've been led to believe by people who should know (a Linux netdev
> > maintainer) that autonegotiation *should* take on the order of 500ms.
> >
> >> 5 - 10 seconds would be
> >> a more conservative default, given that there's no penalty if link-up
> >> occurs before the timeout.
> >
> > Sure, there's no penalty is link-up occurs, but what about all the people
> > for whom link-up doesn't occur -- say, because they're on a wireless link,
> > or their chipset doesn't work right, or it's trying on a link that isn't
> > actually up? Every delay screws them over more and more.
>
> It seems we have a trade-off here.
>
> I think the decision depends on the number of affected users:
>
> - how many will have link-up in less of this time?
Most-to-all.
> - how many chipset has issues with it and will end up getting it in 5
> or 10 secs?
Some-to-none.
> - could it be !wireless specific?
Yes, but that only chops out one subset of cases (link-not-connected will
still take the extra time); I'm also considering switching to use
netif_carrier_ok(), which does work on wireless devices.
- Matt
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