linux-kernel - Re: [PATCH 01/13] [VOYAGER] x86: add {safe,hard}_smp_processor_id to smp

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Date:	Sun, 08 Mar 2009 10:15:11 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 01/13] [VOYAGER] x86: add {safe,hard}_smp_processor_id
 to smp_ops

James Bottomley wrote:
> Not having apics, Voyager can't use the default apic implementation of
> these, it has to read from a special port in the VIC to get the
> processor ID, so abstract these functions in smp_ops to allow voyager
> to live simultaneously with the apic code.
>   

These aren't performance-sensitive at all, are they?  smp_ops is not 
subject to patching/inlining optimisations happen to more hotpath pvops.

Is safe_smp_processor_id needed at all?  It's only got two callers, and 
x86-64 just implements it as smp_processor_id().

> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
> index 035582a..0dfb8c0 100644
> --- a/arch/x86/xen/smp.c
> +++ b/arch/x86/xen/smp.c
> @@ -450,6 +450,11 @@ static irqreturn_t xen_call_function_single_interrupt(int irq, void *dev_id)
>  	return IRQ_HANDLED;
>  }
>  
> +static int xen_hard_smp_processor_id(void)
> +{
> +	return read_apic_id();
> +}
> +
>  static const struct smp_ops xen_smp_ops __initdata = {
>  	.smp_prepare_boot_cpu = xen_smp_prepare_boot_cpu,
>  	.smp_prepare_cpus = xen_smp_prepare_cpus,
> @@ -465,6 +470,8 @@ static const struct smp_ops xen_smp_ops __initdata = {
>  
>  	.send_call_func_ipi = xen_smp_send_call_function_ipi,
>  	.send_call_func_single_ipi = xen_smp_send_call_function_single_ipi,
> +	.hard_smp_processor_id = xen_hard_smp_processor_id,
> +	.safe_smp_processor_id = apic_safe_smp_processor_id,
>   

Hm, there's no meaningful apic-based implementation for these under 
Xen.  DomU has no access to apics, and Dom0's vcpus don't have any fixed 
relationship to physical cpu apics.  They should both just return 
smp_processor_id(), I guess.

    J
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