[maemo-developers] WLAN Horrible Roaming Performance (N800, OS2008), Software or Hardware Problem ?

[From: Siarhei Siamashka]

On Feb 14, 2008 8:43 AM, Kalle Valo <kalle.valo at nokia.com> wrote:
[...]
> > other users reported it too as Luca Olivetti pointed out. and it
> > seems like the problem and fix is described here:
> >
> > http://internettablettalk.com/forums/showpost.php?p=134914&postcount=15
> >
> > at least for the 770 the fix seems to exist,
>
> What I read from the link, someone had written a workaround to try
> again whenever the chip is responding. That would good a feature, but
> I would like to get more information about what's happening in this
> case.

I'm sorry. For some unknown reason, I thought that I notified you
about this problem long ago, but appears that we only discussed this
issue privately with Frantisek Dufka :(

I encountered this problem when I was checking what is the maximum
McBSP clock frequency that could be used reliably on Nokia 770 to
speed up WLAN performance. To do this stability test, I just put the
device on charger, established wlan connection and started a test
script which repeatedly executed wget to download a large file, piping
it to md5sum and verifying that the file always gets received
correctly. That's probably one of the most simple stress tests that
can be done :)

People on ITT, who are suffering from this disconnection problem are
running bittorent client software which probably stresses network to a
much higher extent.

Having kept this simple test running, I noticed that wlan network is
getting stuck eventually. Sometimes very soon and sometimes after a
long time. Checking dmesg log revealed the following lines:
[84936.145721] We haven't got a READY interrupt from WAKEUP. (firmware crashed?)
[84940.419342] TX dropped
[84940.419433] TX dropped

The symptoms are similar to what other people reported as
https://bugs.maemo.org/show_bug.cgi?id=329

Initially I thought that it was the effect of overclocking, but could
reproduce the problem even after going back to the standard frequency.

With a simple patch that just retries operation on such error,
wireless connection got stable. After a long test with the test
script, no problems were detected. The following lines could be
occasionally seen in dmesg log and it  proves that there were
potential connection drops encountered, but they all did not cause any
troubles in reality (MD5 of downloaded file was always OK):
[50559.494232] Dynamic PSM
[50559.494323] PSM timeout 1000 ms
[50622.038146] We haven't got a READY interrupt from WAKEUP. (firmware
crashed?)
[50622.038269] Try again...
[50622.038330] succeeded!!!

I'm attaching the same patch here. It is not very clean, but it does
the job (for Nokia 770).


And I have encountered other problems with WLAN driver that are yet to
be solved. For example, sometimes speed drops to ~30KB/s (that's still
an unresolved mystery to me). Also CPU usage is very high because of
busyloop when waiting till DMA transfer is done. Tasklet, which
executes the code can't be easily preempted, as far as I understand
kernel documentation. Maybe it is possible to split tasklet into
several parts, one of them could be responsible for initiating DMA
transfer, the other could be activated on DMA transfer completion?
This all is important for video streaming as any excessive CPU
resources consumption by WLAN driver negatively impacts video playback
performance.
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