Salut and Suspend/Resume issues

[Sjoerd Simons]

On Tue, Feb 19, 2008 at 09:13:29AM -0500, Chris Ball wrote:
>    > It does feel like we should turn off suspend for some of our
>    > testing.  I've experienced similar problems.
> 
>    > Chris, do you recommend removing ohm? Or is there something else we
>    > should try?
> 
> I recommend fixing the bug.  :)  We know that we intend to have the CPU
> turned off most of the time on our laptops on the mesh -- why is the
> presence service incompatible with this?

It's avahi that's giving you problems. Or more precisely, it can't cope with
the fact that during suspend it's essentially deaf.

If we want to make presence on the local lan work in a way to allow the host
CPU to sleep most of the time we need both a different presence protocol (some
people are already working on this). And we need some assistence from the
wireless card to keep track of presence while the host cpu is asleep.. But i
don't see this happening soon.

> Should we be setting the wireless module to wake on multicast, so that we can
> respond to whatever traffic the presence service is using to see who's
> online?

Yes please do. And if possible only to the multicast traffic the host is
actually interested in.

I'm pretty sure i mentioned this before, if you don't wake up on multicast
traffic your completely breaking the way mdns works. And thus the notions of
presence in a link-local network. Also if you don't wake up on multicast then
activities in a local lan will break as they won't receive data and other
metainformation from other participants.

> Should it be using unicast traffic instead?
No

> What is it in Avahi's code path that causes its peer list to be emptied on
> resume?

Given that it's long suspends that have this problem. It's probably the fact
that the TTL for all contacts has run out, that is causing avahi to flush the
peer list. After which it needs to rediscover all of them. Which is a valid
thing to do, if you've been away for quite some time you have no idea who is
still around.

  Sjoerd
-- 
Matter cannot be created or destroyed, nor can it be returned without a receipt.