Re: [PATCH 5/5] sched: Add laziest preempt model

[Sebastian Andrzej Siewior]

On 2024-10-07 09:46:14 [+0200], Peter Zijlstra wrote:
> Much like LAZY, except lazier still. It will not promote LAZY to full
> preempt on tick and compete with None for suckage.
> 
> (do we really wants this?)

This is like NONE/ VOLUNTARY without the .*_resched().
irqentry_exit_cond_resched() and preempt_schedule.*() does nothing
because only the lazy bit is set. This should trigger all the spots
which were filled with cond_resched() to avoid warnings, right?
There is nothing that will force a preemption, right?

> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
…

The description is the same for two lazy models.

> +config PREEMPT_LAZIEST
> +	bool "Scheduler controlled preemption model"
	bool "Scheduler controlled preemption model (relaxed)"

> +	depends on !ARCH_NO_PREEMPT
> +	depends on ARCH_HAS_PREEMPT_LAZY
> +	select PREEMPT_BUILD if !PREEMPT_DYNAMIC
> +	help
> +	  This option provides a scheduler driven preemption model that
> +	  is fundamentally similar to full preemption, but is least
> +	  eager to preempt SCHED_NORMAL tasks in an attempt to
> +	  reduce lock holder preemption and recover some of the performance
> +	  gains seen from using no preemption.

          The scheduler won't force the task off-CPU if the task does
	  not give up voluntary.
> +
>  endchoice

Sebastian