On 07/31, Frederic Weisbecker wrote:

2014-07-31 20:47 GMT+02:00 Frederic Weisbecker [off-list ref]:

quoted

On Thu, Jul 31, 2014 at 08:12:30PM +0200, Oleg Nesterov wrote:

quoted

On 07/31, Frederic Weisbecker wrote:

No, because preempt_schedule_irq() does the ctx_state save and restore with
exception_enter/exception_exit.

Similar thing happens with schedule_user().

preempt_schedule_irq() handles kernel preemption and schedule_user()
the user preemption. On both cases we save and restore the context
tracking state.

This might be the missing piece you were missing :)

YYYYYEEEEESSSS, thanks!!

And in fact I was going to suggest to add this logic into preempt schedule
paths to improve the situation if we can't make TIF_NOHZ per-cpu.

But Frederic, perhaps I'll return here tomorrow with another question, it
is too late for me now ;)

Thanks!

Oleg.