Re: [PATCH v3] stop_machine: Make migration_cpu_stop() does useful works for CONFIG_PREEMPT_NONE

[Peter Zijlstra]

On Mon, Sep 12, 2016 at 03:05:38PM +0200, Oleg Nesterov wrote:

> But this leads to the question which I wanted to ask many times.
> 
> Why cond_resched() is not NOP if CONFIG_PREEMPT=y ?

Dunno, nobody bothered to do it? We should keep the might_sleep() of
course, but the preemption check is pointless.

> Perhaps we have some users like, just for example,
> 
> 	preempt_enable_no_resched();
> 	cond_resched();
> 
> which actually want the should_resched() check even if CONFIG_PREEMPT,
> but most callers do not?

I would hope not, the few preempt_enable_no_resched() users _should_
have an actual schedule() call in the _very_ near future.