Re: [RFC PATCH 1/3] sched/fair: Call newidle_balance() from finish_task_switch()

[Peter Zijlstra]

On Tue, Apr 28, 2020 at 05:55:03PM -0500, Scott Wood wrote:
> On Wed, 2020-04-29 at 00:09 +0200, Peter Zijlstra wrote:

> > Also, if you move it this late, this is entirely the wrong place. If you
> > do it after the context switch either use the balance_callback or put it
> > in the idle path.
> > 
> > But what Valentin said; this needs a fair bit of support, the whole
> > reason we've never done this is to avoid that double context switch...
> > 
> 
> balance_callback() enters with the rq lock held but BH not separately

BH? softirqs you mean? Pray tell more.

> disabled, which interferes with the ability to enable interrupts but not BH.
> It also gets called from rt_mutex_setprio() and __sched_setscheduler(), and
> I didn't want the caller of those to be stuck with the latency.

You're not reading it right.