Re: [PATCH] net: sched: dev_deactivate_many(): use msleep(1) instead of yield() to wait for outstanding qdisc_run calls

* Marc Kleine-Budde | 2014-03-06 22:39:58 [+0100]:

quoted

Therefore it should allow lower priority threads to run, not just
equal or higher priority ones.

Yes, we need a call that does what you described, however I'm not sure
if yield() really does that. According to:

http://lxr.free-electrons.com/source/kernel/sched/core.c#L3599

quoted

* Typical broken usage is:
*
* while (!event)
*      yield();
*
* where one assumes that yield() will let 'the other' process run that will
* make event true. If the current task is a SCHED_FIFO task that will never
* happen. Never use yield() as a progress guarantee!!

My Process runs with SCHED_FIFO and prio > 50, with IRQ at default prio,
which is 50.

Maybe the RT guys can comment on this. I found another interesting
function in the RT patch set: cpu_chill().

If you boot mainline without -RT, use threadirqs, start your application
do the same prio thing then you should end up with exactly the same
outcome. Please say so :)

msleep() is safe as long as it is used outside of the softirq. Nice that
you found cpu_chill() but on non-RT it turns to cpu_relax() and you do
not want this here.

wait_event() would be nice in the end to have. For now I take that patch
for -RT.

Marc

Sebastian