linux-kernel - Re: [PATCH 1/3] apic: add apic_set_eoi

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Date:	Mon, 16 Jul 2012 11:25:59 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Jacob Pan <jacob.jun.pan@...el.com>,
	Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Joerg Roedel <joerg.roedel@....com>,
	Yinghai Lu <yinghai@...nel.org>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, avi@...hat.com, gleb@...hat.com
Subject: Re: [PATCH 1/3] apic: add apic_set_eoi_write for PV use


* Michael S. Tsirkin <mst@...hat.com> wrote:

> KVM PV EOI optimization overrides eoi_write apic op with its own
> version. Add an API for this to avoid meddling with core x86 apic driver
> data structures directly.
> 
> For KVM use, we don't need any guarantees about when the switch to the
> new op will take place, so it could in theory use this API after SMP init,
> but it currently doesn't, and restricting callers to early init makes it
> clear that it's safe as it won't race with actual APIC driver use.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  arch/x86/include/asm/apic.h |  3 +++
>  arch/x86/kernel/apic/apic.c | 17 +++++++++++++++++
>  2 files changed, 20 insertions(+)
> 
> diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
> index aa5b2ee..ff8dff6 100644
> --- a/arch/x86/include/asm/apic.h
> +++ b/arch/x86/include/asm/apic.h
> @@ -469,6 +469,8 @@ static inline u32 safe_apic_wait_icr_idle(void)
>  	return apic->safe_wait_icr_idle();
>  }
>  
> +extern void __init apic_set_eoi_write(void (*eoi_write)(u32 reg, u32 v));
> +
>  #else /* CONFIG_X86_LOCAL_APIC */
>  
>  static inline u32 apic_read(u32 reg) { return 0; }
> @@ -478,6 +480,7 @@ static inline u64 apic_icr_read(void) { return 0; }
>  static inline void apic_icr_write(u32 low, u32 high) { }
>  static inline void apic_wait_icr_idle(void) { }
>  static inline u32 safe_apic_wait_icr_idle(void) { return 0; }
> +static inline void apic_set_eoi_write(void (*eoi_write)(u32 reg, u32 v)) {}
>  
>  #endif /* CONFIG_X86_LOCAL_APIC */
>  
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 39a222e..c7520b6 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2124,6 +2124,23 @@ void default_init_apic_ldr(void)
>  }
>  
>  /*
> + * Override the generic EOI implementation with an optimized version.
> + * Only called during early boot when only one CPU is active and with
> + * interrupts disabled, so we know this does not race with actual APIC driver
> + * use.
> + */
> +void __init apic_set_eoi_write(void (*eoi_write)(u32 reg, u32 v))
> +{
> +	struct apic **drv;
> +
> +	for (drv = __apicdrivers; drv < __apicdrivers_end; drv++) {
> +		/* Should happen once for each apic */
> +		WARN_ON((*drv)->eoi_write == eoi_write);
> +		(*drv)->eoi_write = eoi_write;
> +	}
> +}
> +

ok, it's better this way.

Acked-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo
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