linux-kernel - [PATCH] - Increase MAX_APICS for very large x86

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Message-ID: <20080616170910.GA24930@sgi.com>
Date:	Mon, 16 Jun 2008 12:09:10 -0500
From:	Jack Steiner <steiner@....com>
To:	mingo@...e.hu, tglx@...utronix.de
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] - Increase MAX_APICS for very large x86_64 configs

Increase the maximum number of apics when running very large
configurations. This patch has no affect on most systems.

Signed-off-by: Jack Steiner <steiner@....com>

---

The patch has no effect on any 32-bit kernel. It adds ~4k to the size
of 64-bit kernels but only if NR_CPUS > 255.

This is a repost of an earlier patch (4/16) that  was implicated in
a random-qa failure. I have not been able to reproduce the failure
using the same boot args & config.  Best guess is that some other
patch caused random data corruption & this patch was a victim.



 include/asm-x86/mpspec_def.h |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

Index: linux/include/asm-x86/mpspec_def.h
===================================================================
--- linux.orig/include/asm-x86/mpspec_def.h	2008-06-08 09:05:51.140046529 -0500
+++ linux/include/asm-x86/mpspec_def.h	2008-06-08 09:05:55.244550306 -0500
@@ -17,10 +17,11 @@
 # define MAX_MPC_ENTRY 1024
 # define MAX_APICS      256
 #else
-/*
- * A maximum of 255 APICs with the current APIC ID architecture.
- */
-# define MAX_APICS 255
+# if NR_CPUS <= 255
+#  define MAX_APICS     255
+# else
+#  define MAX_APICS   32768
+# endif
 #endif
 
 struct intel_mp_floating {
--
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