linux-kernel - [PATCH] x86: bump default NR_CPUS for 64-bit configuration

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Message-Id: <1431080745-19792-1-git-send-email-kirill.shutemov@linux.intel.com>
Date:	Fri,  8 May 2015 13:25:45 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH] x86: bump default NR_CPUS for 64-bit configuration

Default NR_CPUS==8 is not enough to cover high-end desktop
configuration: Haswell-E has upto 16 threads.

Let's increase default NR_CPUS to 64 on 64-bit configuration. With this
value CPU bitmask will still fit into one unsinged long.

Default for 32-bit configuration is still 8: it's unlikely anybody will
run 32-bit kernel on modern hardware.

As alternative we could bump NR_CPUS to 128 to cover all dual-processor
servers with some margin.

For reference: Debian and Suse build their kernels with NR_CPUS==512,
Fedora -- 1024.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 arch/x86/Kconfig | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 6aaf38ac417d..c3333e5be5d7 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -851,7 +851,8 @@ config NR_CPUS
 	default "1" if !SMP
 	default "8192" if MAXSMP
 	default "32" if SMP && X86_BIGSMP
-	default "8" if SMP
+	default "8" if SMP && X86_32
+	default "64" if SMP
 	---help---
 	  This allows you to specify the maximum number of CPUs which this
 	  kernel will support.  If CPUMASK_OFFSTACK is enabled, the maximum
-- 
2.1.4

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