scheduler priority of 'parked' threads

[David Laight <david%l8s.co.uk@localhost>]

I've noticed something 'odd' about the priority 'top' reports for
parked threads.

Processes sleeping in in select, wait, kqueue (etc) all have
priorites of around 85, but those sleeping in 'parked' (waiting
for a pthread mutex/condvar) have a priority of around 43.

I think the 85 is an 'elevated' priority so that the process
it likely to be scheduled when woken - to improve interactive
responsiveness.

The 43 is a normal kernel 'running' priority, such a process won't
pre-empt anything else - so will only run if there is a spare cpu
or when the scheduler runs on a timer tick.

This might be one reason the X server is unresponsive (but it also
chews through a lot of cpu).

        David

-- 
David Laight: david%l8s.co.uk@localhost