Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice

[Peter Zijlstra]

On Thu, Feb 06, 2025 at 02:53:53PM +0100, Sebastian Andrzej Siewior wrote:
> On 2025-02-06 14:48:59 [+0100], Peter Zijlstra wrote:
> > On Thu, Feb 06, 2025 at 02:44:08PM +0100, Sebastian Andrzej Siewior wrote:
> > > SCHED_OTHER vs SCHED_OTHER after all. But please don't delay a wakeup of
> > > SCHED_FIFO/ RR/ DL because of this LAZY hint.
> > 
> > Thing will get delayed if interrupts are disabled or kernel has
> > preemption disabled too. So as long as we ensure hint crap is of equal
> > order, nothing cares if you do.
> > 
> > If you can't tell the difference between task does hint crap in
> > userspace and task is in the middle of syscall, you can't tell the
> > difference.
> 
> I can tell the difference if I see a trace where an interrupt fires,
> performs a wakeup and the SCHED_OTHER task remains on CPU while the task
> SCHED_FIFO task sits on the runqueue until a timer fires.

Right, but so what? Same delay will happen if interrupt fires in the
middle of a preempt_disable() region.

Or if interrupt gets pending while interrupts are disabled, except your
trace will not show that.

Your worst case response time isn't affected. That's all that matters.