linux-kernel - Re: [patch 00/26] x64, x2apic/intr-remap: Interrupt-remapping and x2apic support

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Message-ID: <20080713010059.GB1678@linux-os.sc.intel.com>
Date:	Sat, 12 Jul 2008 18:01:00 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Yinghai Lu <yhlu.kernel@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>, "hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"steiner@....com" <steiner@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jeremy@...p.org" <jeremy@...p.org>
Subject: Re: [patch 00/26] x64, x2apic/intr-remap: Interrupt-remapping and x2apic support

On Sat, Jul 12, 2008 at 12:49:53AM -0700, Yinghai Lu wrote:
> On Sat, Jul 12, 2008 at 12:02 AM, Eric W. Biederman
> <ebiederm@...ssion.com> wrote:
> > "Yinghai Lu" <yhlu.kernel@...il.com> writes:
> >
> >> On Fri, Jul 11, 2008 at 8:52 PM, Eric W. Biederman
> >> <ebiederm@...ssion.com> wrote:
> >>> "Yinghai Lu" <yhlu.kernel@...il.com> writes:
> >>>
> >>>> 1. wonder if x2apic can be use with uniprocessor.
> >>>>
> >>>> in APIC_init_uniprocessor, it will try to enable x2apic, but later
> >>>>
> >>>> apic_write(APIC_ID, SET_APIC_ID(boot_cpu_physical_apicid));
> >>>>
> >>>> but SET_APIC_ID is still for xapic version. so need to GET_APIC_ID,
> >>>> SET_APIC_ID for different
> >>>> genapic like 32bit.
> >>>>
> >>>> 2 check_x2apic is called in setup_arch, but it only set apic_ops,
> >>>> and genapic still not changed, aka apic_flat...
> >>>> wonder if you need to call setup_apic_routing to set genapic.
> >>>>
> >>>> otherwise read_apic_id could have use the one from apic_flat....need
> >>>> to shift......
> >>>>
> >>>> 3.or move read_apic_id to apic_ops intead...together with GET_APIC_ID too.
> >>>> but 32bit version seems like to put GET_APIC_ID with genapic...
> >>>>
> >>>> which one is better? 2 or 3
> >>>
> >>> Z finish untangle SMP support from apic initialization and move the apic
> >>> initialization up into init_IRQ.
> >>>
> >>> That is better but is likely the wrong short term approach.
> >>
> >> plan to add get_apic_id(x) into 64bit genapic, and will use
> >> #define GET_APIC_ID(x) genapic->get_apic_id(x)
> >> #define read_apic_id() GET_APIC_ID(apic_read(APIC_ID))
> >>
> >> so it is identical to 32bit, and we smooth the merging of 32/64 apic code
> >>
> >> also read the x2APIC spec pdf, it doesn't say anything about interrupt
> >> remapping...need to be used with x2apic...
> >
> > Clustered logical mode won't work as it requires > 16 bits of apicid.
> > So only flat physical mode will work.
> 
> current read_apic_id in genx2apic_cluster and genx2apic_phys is the same...

read_apic_id() corresponds to physical apic id and it is same
irrespective of whether we use logical cluster mode or physical mode.

thanks,
suresh
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