Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933227AbbELR5Q (ORCPT ); Tue, 12 May 2015 13:57:16 -0400 Received: from mail-ob0-f170.google.com ([209.85.214.170]:33441 "EHLO mail-ob0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932788AbbELR5P (ORCPT ); Tue, 12 May 2015 13:57:15 -0400 MIME-Version: 1.0 In-Reply-To: <1431080745-19792-1-git-send-email-kirill.shutemov@linux.intel.com> References: <1431080745-19792-1-git-send-email-kirill.shutemov@linux.intel.com> Date: Tue, 12 May 2015 13:57:14 -0400 X-Google-Sender-Auth: tRUOC9w9ZAp7mDSUoG_yEP_SSCg Message-ID: Subject: Re: [PATCH] x86: bump default NR_CPUS for 64-bit configuration From: Josh Boyer To: "Kirill A. Shutemov" Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86 , "Linux-Kernel@Vger. Kernel. Org" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2287 Lines: 59 On Fri, May 8, 2015 at 6:25 AM, Kirill A. Shutemov wrote: > 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. FWIW, we're carrying a patch that drops the "if DEBUG_PER_CPU_MAPS" dependency for CPUMASK_OFFSTACK to allow us to set that to 1024 without bringing in debug junk. I sent this patch a long time ago and Ingo and Linus said it was stupid and it should be auto-selected. Ingo was going to poke at it IIRC how the thread ended, because I couldn't see a clean way to make Kconfig do what we wanted. josh > > Signed-off-by: Kirill A. Shutemov > --- > 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 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/