2015-05-13 12:23:27

by Purcareata Bogdan

Subject: Re: [PATCH] powerpc/mpic: Remove WHOAMI readback after EOI

Ping?

On 24.03.2015 12:43, Bogdan Purcareata wrote:
> After previous discussions regarding the subject [1][2], there's no clear
> explanation or reason why the call was needed in the first place. The sensible
> argument is some sort of synchronization between the CPU and the MPIC, which
> hasn't been pointed out precisely and is no longer required (at least on BookE
> platforms).
>
> The benefit of this change is saving a MMIO trap per interrupt when running in a
> KVM guest.
>
> [1] https://patchwork.ozlabs.org/patch/429098/
> [2] https://patchwork.ozlabs.org/patch/433557/
>
> Signed-off-by: Bogdan Purcareata <[email protected]>
> ---
> arch/powerpc/sysdev/mpic.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/arch/powerpc/sysdev/mpic.c b/arch/powerpc/sysdev/mpic.c
> index bbfbbf2..045e72a9 100644
> --- a/arch/powerpc/sysdev/mpic.c
> +++ b/arch/powerpc/sysdev/mpic.c
> @@ -655,7 +655,6 @@ static inline struct mpic * mpic_from_irq_data(struct irq_data *d)
> static inline void mpic_eoi(struct mpic *mpic)
> {
> mpic_cpu_write(MPIC_INFO(CPU_EOI), 0);
> - (void)mpic_cpu_read(MPIC_INFO(CPU_WHOAMI));
> }
>
> /*
>

2015-05-13 16:34:13

by Scott Wood

Subject: Re: [PATCH] powerpc/mpic: Remove WHOAMI readback after EOI

On Wed, 2015-05-13 at 15:23 +0300, Purcareata Bogdan wrote:
> Ping?
>
> On 24.03.2015 12:43, Bogdan Purcareata wrote:
> > After previous discussions regarding the subject [1][2], there's no clear
> > explanation or reason why the call was needed in the first place. The sensible
> > argument is some sort of synchronization between the CPU and the MPIC, which
> > hasn't been pointed out precisely and is no longer required (at least on BookE
> > platforms).
> >
> > The benefit of this change is saving a MMIO trap per interrupt when running in a
> > KVM guest.
> >
> > [1] https://patchwork.ozlabs.org/patch/429098/
> > [2] https://patchwork.ozlabs.org/patch/433557/
> >
> > Signed-off-by: Bogdan Purcareata <[email protected]>
> > ---
> > arch/powerpc/sysdev/mpic.c | 1 -
> > 1 file changed, 1 deletion(-)

Don't top-post.

This is commit 56302c53d3dc477b8360954fc92c1dfc4fc0ec54 in Linus's tree.

-Scott