Salut and Suspend/Resume issues

[Giannis Galanis]

On Feb 19, 2008 10:13 AM, Ricardo Carrano <carrano at ricardocarrano.com>
wrote:

>
> I was asking whether it would help to have the wireless module wake us
> > on multicast packets instead of only unicast.  Are you saying that it
> > would?
>
>
> It seems so, though it would, as John points out, make resumes far more
> constant. It seems we have to find a creative way out of this tough choice
> (automated suspend vs mesh) or face it.
>
>
> >
> >
> >   > Avahi entries will expire after some time. Suspend will prevent it
> >   > to update its cache.
> >
> > Yani's bug report (#6467) suggests that Avahi entries often expire
> > immediately upon resume:
> >
> >   After the XO resumes (probably after beinng suspended for several
> >   minutes) all the icons in the mesh view vanish, except the mesh
> >   circles.
>
>
> I read this as the avahi-cache  expiring its entries.  Yanni  can  you put
> timeframes on this?
> Could check how long does it take to expiry an entry (TO) and then check
> if:
> Suspend time > TO -> all entries vanish
> Suspend time << TO -> no entries vanish
> Supens time ~ TO -> some entries vanish
>

There as 2 cases where icons vanish due to suspend.

1st: The moment you resume(it generally happens after long suspends), all
icons vanish instantly(APs/XOs). This bug (#6467) suggests that sugar has a
problem with suspend resume.
The icons slowly reappear. I assume that if the avahi peer list is intact
that all XOs return.

2nd: The avahi list smtimes looses some or all of the peers at resume. This
is also under 6467, but it seems technicaly different. One possible
explanation could be that during suspend th XO resumes several times, but i
didnt notice it! And within this time frames it realized that the other
suspended XOs are gone, so it cleared its cache. Now when I resumed it
myself, I observed that the cache is clean!!

Now, regarding the timeouts of avahi. This is a 3rd thing:
When an XO leaves the channel we have 4 states:
   mm:ss
1. 00:00  XO leave the channel(manually/or ti suspended)
2. 10:00  Avahi notices teh XO left, and reports it as "failed"
3. 30:00  Icon dissappears in the mesh view
4. 60:00  Avahi cache is cleared
Additionally there is a bug(#5501) according to which, is a NEW XO arrives
between states 2 and 3, then instantly ALL "failed" avahi peers are cleared
and the corresponding icons vanish.

So, the 3rd case is the following:

Assume a mesh has e.g. 20 XOs, and I use my XO so it doesnt suspend, but the
rest 19 of them are suspended.
If in >10mins a new XO arrives, then all the 19 XOs instantly vanish from
the mesh.

So the TO time is between 10->30min... but closer to 10min if many XOs
suspend/resume
So if resume time << 10min everything is fine!!



What i dont know is when an XO resumes if it sends any avahi packet no
notify tis presence/return. Because if it doesnt, then the XO wont exist int
he others cache list, so the others wont search for it.
Sjoerd, can you answer this?

This would explain why after resume some XOs take tooo long to see each
other again.
If you combine this with the "2nd" case, you will see that in the natural
case that XOs will resume at random points in time by the user, they will
all clear their cache, unless they resume concurrently.
So in the end, all will have empty caches!!




>
> >
> > Thanks,
> >
> > - Chris.
> > --
> > Chris Ball   <cjb at laptop.org>
> >
>
>
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