Re: [PATCH] x86: Allow NR_CPUS=1024

From: Russ Anderson <rja@sgi.com>
To: Josh Boyer <jwboyer@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	prarit@redhat.com, x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86: Allow NR_CPUS=1024
Date: Mon, 4 Nov 2013 09:56:24 -0600	[thread overview]
Message-ID: <20131104155624.GA31656@sgi.com> (raw)
In-Reply-To: <20131104141615.GD9944@hansolo.jdub.homelinux.org>

On Mon, Nov 04, 2013 at 09:16:16AM -0500, Josh Boyer wrote:
> On Mon, Nov 04, 2013 at 03:10:51PM +0100, Ingo Molnar wrote:
> > * Josh Boyer <jwboyer@redhat.com> wrote:
> > 
> > > > Why touch MAXSMP at all? It's really just a shortcut for 'configure 
> > > > the kernel silly large', via a single option, nothing else. You are 
> > > > not forced to use it and it should not affect configurability of 
> > > > NR_CPUS.
> > > >
> > > > What we _really_ want here is to fix NR_CPUS setting: to extend its 
> > > > range and to enforce that NR_CPUS cannot be set larger than 512 
> > > > without setting CONFIG_CPUMASK_OFFSTACK.
> > > 
> > > OK.  I was just thinking that if we've come to the conclusion that 4096 
> > > CPUs isn't silly large anymore, we should make MAXSMP be something we 
> > > consider silly large. [...]
> > 
> > MAXSMP is also supposed to track the real hardware max as well on x86 - 
> > i.e. we should only increase it to 8192 etc. if such hardware exists.
> 
> Russ, does SGI (or anyone else that you know of) have x86 hardware with
> more than 4096 CPUs?

Yes.  We have a system in the lab with 254 12-core IVB sockets for
a total of 3048 cores.  With HT is it 6096 cpus.

> If so, I can actually make a bump to the MAXSMP count a separate patch.
> 
> josh

-- 
Russ Anderson, OS RAS/Partitioning Project Lead  
SGI - Silicon Graphics Inc          rja@sgi.com