On 17/07/2019 09:43, Thomas Gleixner wrote:
> When preempt_count is zero on return from interrupt then
> schedule_preempt_irq() is invoked even if TIF_NEED_RESCHED is not set.
>
> That does not make sense because schedule_preempt_irq() has to go through a
> full __schedule() for nothing in that case.
>
> Check TIF_NEED_RESCHED and invoke schedule_preempt_irq() only if set.
>
> Signed-off-by: Thomas Gleixner <t...@linutronix.de>
Don't we have NEED_RESCHED squashed into preempt count?
396244692232 ("arm64: preempt: Provide our own implementation of
asm/preempt.h")
So the existing check should cover that, unless I'm missing something?
> ---
> Found while staring at some RT wrecakge in that area.
> ---
> arch/arm64/kernel/entry.S | 4 ++++
> 1 file changed, 4 insertions(+)
>
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -680,6 +680,10 @@ alternative_if ARM64_HAS_IRQ_PRIO_MASKIN
> orr x24, x24, x0
> alternative_else_nop_endif
> cbnz x24, 1f // preempt count != 0 || NMI
> return path
> +
> + ldr x0, [tsk, #TSK_TI_FLAGS] // get flags
> + tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling?
> +
> bl preempt_schedule_irq // irq en/disable is done inside
> 1:
> #endif
>
