linux-kernel - [patch] genapic: default to physical mode on hotplug CPU kernels

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Date:	Tue, 28 Nov 2006 21:23:22 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
Cc:	mm-commits@...r.kernel.org, ak@...e.de, ashok.raj@...el.com,
	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: [patch] genapic: default to physical mode on hotplug CPU kernels


* Siddha, Suresh B <suresh.b.siddha@...el.com> wrote:

> On Tue, Nov 28, 2006 at 07:33:46AM +0100, Ingo Molnar wrote:
> > -	if (clusters <= 1 && max_cluster <= 8 && cluster_cnt[0] == max_cluster)
> > +	if (max_apic < 8)
> 
> Patch mostly looks good.  Instead of checking for max_apic, can we use
> 	cpus_weight(cpu_possible_map) <= 8

ok - but i think it's still possible the BIOS tells us APIC IDs that are 
larger than 7, even if there are fewer CPUs. So i think the patch below 
should cover it. Agreed?

	Ingo

-------------------->
From: Ingo Molnar <mingo@...e.hu>
Subject: [patch] genapic: default to physical mode on hotplug CPU kernels

default to physical mode on hotplug CPU kernels.

Signed-off-by: Ingo Molnar <mingo@...e.hu>

Index: linux/arch/x86_64/kernel/genapic.c
===================================================================
--- linux.orig/arch/x86_64/kernel/genapic.c
+++ linux/arch/x86_64/kernel/genapic.c
@@ -51,7 +51,7 @@ void __init clustered_apic_check(void)
 			max_apic = id;
 	}
 
-	if (max_apic < 8)
+	if (max_apic < 8 && cpus_weight(cpu_possible_map) <= 8)
 		genapic = &apic_flat;
 	else
 		genapic = &apic_physflat;
-
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