SMP report

Jouni Malinen jkmaline at cc.hut.fi
Mon Aug 18 22:56:00 EDT 2003


On Sun, Aug 17, 2003 at 08:24:47PM +1000, James Harper wrote:

> I'm running 2.6.0-test3 with the latest cvs version of hostap on an SMP 
> system and it appears much more stable than previous versions. I just 
> tried a flood ping for a few minutes and the only error I got was:
> 
> Aug 17 20:19:17 portal kernel: wlan0: hfa384x_cmd_issue: cmd reg was 
> busy for 1 usec

I'm not fully sure about what caused this, but with busy waiting for the
command reg, this should be fine.

> Aug 17 20:20:53 portal kernel: wlan0: detected fid change (try=0, 
> reg=0044): 0166 a5a4 0166
> Aug 17 20:20:59 portal kernel: wlan0: detected fid change (try=0, 
> reg=0040): 0000 03d6 03d6
> 
> which probably isn't good but previously I would be getting card resets 
> and/or crashes etc all over the place.

That's good, well, at least useful, to know. So, there are at least two
different SMP hosts that report changing fid registers and I haven't
heard of a single one without this "feature".. This looks like a
hardware bug to me since those registers should not really change its
value even if something is being read from the card (or written to it)
at the same time; as long as the RX/TX/Info event has not been ACKed
(and it will be ACKed only after reading those fid registers).

In other words, I apparently do need to leave that workaround code in
the driver, although probably with ifdefs for including it only to
hostap_pci and only when kernel is compiled with SMP support..

Getting those fid reads returning proper values will certainly remove
quite a few hw_resets and will thus help with the stability. The other
issue, i.e., system lockup on hw_reset, may however still exist. I
actually have couple of patches that could be tested on top of 0.0.4
release so that we could try to find a way to avoid the crash. If
someone with an SMP system using hostap_pci is willing to test these,
please let me know and I'll send the patches. Please note that testing
these will most probably end up crashing your system number of times..

-- 
Jouni Malinen                                            PGP id EFC895FA



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