Re: [PATCH 1/9] iwlagn: need longer tx queue stuck timer for coex devices

[Stanislaw Gruszka <sgruszka@redhat.com>]

Wey,

On Thu, Oct 14, 2010 at 11:02:42AM -0700, Wey-Yi Guy wrote:
> For BT/WiFi combo devices, need longer tx stuck queue
> timer, so those devices won't reload firmware too often.

Seeing how many tweaking queue hung monitoring we need, I started
to think that the watchdog design is not so good. Currently we compare 
q->read_ptr with q->last_read_ptr, and if they match 3 times in a row
during 200ms, we assume firmware hung. But maybe 200ms of no read_ptr
activity is too small time for device. Moreover we have unlikely but
possible situation when device is fully functional, but read_ptr will
wrap by accident to q->last_read_ptr on every check.

I think, better solution would be something like in rt2x00 or in 
net/sched/sch_generic.c (however rt2x00 is easier to understand). It is
based on time stamp. When we get tx complete notification from hardware
(and incise read_ptr) mark the time stamp. In watchdog, which tick
periodically, check if queue is not empty and if current time is
bigger than time_stamp + time_out, if it is - firmware hung. More
smaller watchog tick give more precise hung detect (with disadvantage
of more cpu usage).

Stanislaw