Interrupt Latency on PPC

[Till Straumann]

Things get _really_ bad when the PTY driver is
heavily used. I measured IRQ latencies of ~200us
during quite short measurement intervals (remember,
we're doing statistics here). This is in the order of
100 times the average.

I guess that the problem is caused by termios.c
which under some circumstances calls the
device's 'write' callback with _IRQs_disabled_.
The PTY driver's write callback is a

write(socket,...)

outchh!

Is there a termios expert out there who could explain
to me what really needs to be protected from interrupts?

Also, shouldn't the PTY driver run in task driven
(as opposed to the current IRQ driven) mode?

-- Till.