[ltp] Interference of wlan usage and hdaps?

[Elias Oltmanns]

Hi folks,

the USB controller on my X40 has been fried, it seems, last week.
Fortunately, I have been able to switch to another X40 by swapping HDs
temporarily. Since this is an oldish machine too and since X40-s seem to
be prone to USB failure, I'll most likely get something new (perhaps a
X200s) as I make heavy use of the USB port(s). So much for the preface
to the narrative. I really wanted to tell you about an observation I
made in passing and ask if you can confirm a suspicion of mine.

Up to this unpleasant incident last week, I used to run a 2.6.27 kernel
with a set of patches, all in all virtually unchanged since the
beginning of this year. The switch to that other X40 required a
recompile because I had to enable support for the intel wireless driver
(rather than atheros). I took this opportunity to have a go at 2.6.30.7.
The rather annoying result of it all is that hdapsd frequently parks the
disk heads, sometimes preventing all I/O for tens of seconds without
interruption. Clearly, this strange behaviour only occurs once I have
connected to my wlan and goes on persistently afterwards, irrespective
of the current state of the wlan interface.

Almost a year ago, I had observed a similar behaviour on my original X40
featuring an Atheros pci card. It took me some time to identify the
actual culprit and to point the finger. Unfortunately, the problem
turned out to be inherently linked with the design of the atheros driver
(or parts of it) and nontrivial to solve. Now, I'm lead to believe that
other wlan drivers (namely iwp2200) have similar design flaws. As I am
currently (and will be for some time) unable to dedicate my time to
extensive investigations, let alone writing patches, I wanted to ask
whether anyone can confirm these observations on different hardware /
kernel combinations before I go bothering people at the linux-wireless
list. Here is my test sequence:

1. Boot system, make sure that it won't fire up wlan devices (just
   loading modules is alright);
2. make sure that hdapsd is running, system should behave normally, i.e.
   no head parking while working on a solid desk; naturally, you have to
   exercise the disk, so it won't park the heads after being idle for
   some time;
3. associate to your wlan (actually, scanning for available networks
   should be sufficient);
4. check whether hdapsd begins to park disk heads without obvious cause;
   it may take some time before it begins to do so; also check whether
   this behaviour persists when shutting down the wlan interface.

Apparently, this issue has not come up so far, which rather surprises
me. Perhaps there aren't that many hdaps users after all, or they aren't
heavy wlan usres. But then, it is perfectly possible that I have missed
something as I'm following developments and discussions rather
sluggishly these days due to time constraints.

Any input would be appreciated,

Elias