linux-kernel - Re: [patch] genapic: optimize & fix APIC mode setup

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Message-ID: <20061113103051.D17720@unix-os.sc.intel.com>
Date:	Mon, 13 Nov 2006 10:30:51 -0800
From:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org, ashok.raj@...el.com
Subject: Re: [patch] genapic: optimize & fix APIC mode setup

On Mon, Nov 13, 2006 at 07:42:56PM +0100, Ingo Molnar wrote:
> * Siddha, Suresh B <suresh.b.siddha@...el.com> wrote:
> > Not really. That chipset belongs to a MP platform and with your 
> > proposed patch, we will endup using clustered APIC mode and will hit 
> > the issue(in the presence of cpu hotplug) mentioned in that URL.
> 
> hm, why does it end up in clustered mode? Cluster mode should only 
> trigger if the APIC IDs go beyond 16.

go beyond '8' not 16. With Dual-core+HT these MP platforms will have 16 logical
cpus.

> 
> but i'd be fine with never going into cluster mode, instead always using 
> physical flat mode when having more than 8 APICs (independent of the 
> presence of CPU hotplug). On small systems, logical flat mode is what is 
> the best-tested variant (it's also slightly faster).

Ok.

thanks,
suresh
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