"event-scan failed" logflood

[Benjamin Herrenschmidt]

On Thu, 2010-05-13 at 06:16 -0500, pacman at kosh.dhis.org wrote:
> Benjamin Herrenschmidt writes:
> > 
> > Well, first it should be called once per second, not 60 times per
> > second, so something is wrong there...
> 
> Actually I think it was happening a lot more than 60 times per second, and
> klogd was losing most of the messages because they came too fast. When
> running the new kernel, vmstat shows 170000 context switches per second (and
> CPU usage never going below 5%) even when everything should be idle.
> 
> My next experiment was to hack rtas_init to return 0 unconditionally. Now
> everything still runs fine, and the context switches per second are back down
> in the 2-digit range.
> 
> > 
> > Then, it wouldn't surprise me if the Pegasos RTAS didn't implement
> > the event scan properly. Maybe we failed silently before that ? I
> > doubt it's necessary there anyways.
> 
> If I'm reading things correctly, rtas-event-scan-rate is the key to the
> frequency of attempts. And rtasd.c didn't expect this:
> 
> $ od -t x1 /proc/device-tree/rtas/rtas-event-scan-rate
> 0000000 00 00 00 00
> 0000004

Ok, that gives us a good thing to use to not do the scanning then. If
that's 0 then we assume it's a bogus OF and we disable the scan
completely. I'll do a patch later today, though feel free to beat me to
it.

Cheers,
Ben.