linux-kernel - Re: [PATCH v2 2/2] vsmp: Ignore IOAPIC IRQ affinity if possible

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Message-ID: <20120509091827.GB8585@gmail.com>
Date:	Wed, 9 May 2012 11:18:27 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	"Shai Fultheim (Shai@...leMP.com)" <Shai@...leMP.com>
Cc:	Ido Yariv <ido@...ery.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ravikiran Thirumalai <kiran.thirumalai@...il.com>
Subject: Re: [PATCH v2 2/2] vsmp: Ignore IOAPIC IRQ affinity if possible


* Shai Fultheim (Shai@...leMP.com) <Shai@...leMP.com> wrote:

> Ingo Molnar <mingo.kernel.org@...il.com> wrote:
> > * Ido Yariv <ido@...ery.com> wrote:
> 
> > > @@ -51,6 +60,7 @@ void __init default_setup_apic_routing(void)
> > >  	if (is_vsmp_box()) {
> > >  		/* need to update phys_pkg_id */
> > >  		apic->phys_pkg_id = apicid_phys_pkg_id;
> > > +		apic->vector_allocation_domain =
> > fill_vector_allocation_domain;
> > >  	}
> > >  }
> > 
> > This is_vsmp_box() special case should really move into its own
> > apic handler.
> > 
> > Thanks,
> 
> Ingo,
> 
> vSMP Foundation virtualize multiple systems as one.  The Guest 
> OS is using the underlying hardware APIC driver, and therefore 
> we must allow the various APIC drivers to kick in.  When using 
> vSMP Foundation APIC driver is selected by the kernel based on 
> the hardware that is being virtualized, and that can be APIC, 
> X2APIC phys, X2APIC cluster, summit, etc.
> 
> If we would to implement an APIC handler, we would not be able 
> to use the native hardware APIC driver (unless we do an ugly 
> hack).

If you need a callback on that level then there's a cleaner 
mechanism than open-coding vsmp handlers into generic code:

 - create a new platform callback in x86_platform_ops
 - call it from apic_64.c if set
 - fill in the vSMP specific handler from the vSMP init code

Thanks,

	Ingo
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