On Thu, 2010-05-13 at 06:16 -0500, pacman@kosh.dhis.org wrote:

Benjamin Herrenschmidt writes:

quoted

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.

quoted

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.