Re: [Xen-devel] [PATCH] gic: drop interrupts enabling on interrupts processing

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 21/12/2018 17:41, Andrii Anisov wrote:
> From: Andrii Anisov <andrii_anisov@xxxxxxxx>
>
> This reduces the number of context switches in case we have coming guest
> interrupts from different sources at a high rate. What is likely for
> multimedia use-cases.
> Having irqs unlocked here makes us go through trap path again in case we
> have a new guest interrupt arrived (even with the same priority, after
> `desc->handler->end(desc)` in `do_IRQ()`), what is just a processor
> cycles wasting. We will catch them all in the `gic_interrupt() function
> loop anyway. And the guest irqs arrival prioritization is meaningless
> here, it is only effective at guest's level.
>
> Signed-off-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
>
> ---
>
> This is the patch [1] from RFC series, with extended commit message.
>
> [1] https://lists.xenproject.org/archives/html/xen-devel/2018-11/msg03286.html
>
> ---
>   xen/arch/arm/gic.c | 2 --
>   1 file changed, 2 deletions(-)
>
> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
> index 6cc7dec..9f5cd95 100644
> --- a/xen/arch/arm/gic.c
> +++ b/xen/arch/arm/gic.c
> @@ -386,10 +386,8 @@ void gic_interrupt(struct cpu_user_regs *regs, int is_fiq)
>   
>           if ( likely(irq >= 16 && irq < 1020) )
>           {
> -            local_irq_enable();
>               isb();
>               do_IRQ(regs, irq, is_fiq);
> -            local_irq_disable();
>           }
>           else if ( is_lpi(irq) )
>           {
I think it would make sense to keep the interrupts disabled in is_lpi as well. 
So we keep the behavior the same accross all interrupts.
Cheers,

--
Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel