From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752797AbcCRMjY (ORCPT <rfc822;w@1wt.eu>);
	Fri, 18 Mar 2016 08:39:24 -0400
Received: from mail-wm0-f45.google.com ([74.125.82.45]:32841 "EHLO
	mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751838AbcCRMjU (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 18 Mar 2016 08:39:20 -0400
Message-ID: <1458304756.3600.3.camel@gmail.com>
Subject: Re: 4.5.0+ panic when setup loop device
From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Xiong Zhou <jencce.kernel@gmail.com>, Thomas Gleixner <tglx@linutronix.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Andreas Herrmann <aherrmann@suse.com>
Date: Fri, 18 Mar 2016 13:39:16 +0100
In-Reply-To: <20160318101559.GG6344@twins.programming.kicks-ass.net>
References: <CADJHv_ty-8OsX3YKKYg4vtzcL-Hmag3rtjObbcgFLE-KLt1M7g@mail.gmail.com>
	 <alpine.DEB.2.11.1603161624280.3978@nanos>
	 <CADJHv_s1cM=NxkCSHEm_1MctDYJUkDtutLB=aFtx9rB4a3FZdw@mail.gmail.com>
	 <20160317095220.GO6344@twins.programming.kicks-ass.net>
	 <1458274314.3859.25.camel@gmail.com>
	 <20160318101559.GG6344@twins.programming.kicks-ass.net>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.16.5 
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, 2016-03-18 at 11:15 +0100, Peter Zijlstra wrote:
> On Fri, Mar 18, 2016 at 05:11:54AM +0100, Mike Galbraith wrote:
> > On Thu, 2016-03-17 at 10:52 +0100, Peter Zijlstra wrote:
> > 
> > > Andreas; Borislav said to Cc you since you wrote all this.
> > > The issue is that Linux assumes:
> > > 
> > > 	> nr_logical_cpus = nr_cores * nr_siblings
> > 
> > It also seems to now assume that if SMT is possible, it's enabled.
> > 
> > Below is my 8 socket DL980 G7, which has SMT turned off for RT
> > testing,
> > booting NOPREEMPT master tuned for maximum bloat ala distro and
> > getting
> > confused by me telling it (as always) nr_cpus=64.  Bad juju ensues.
> 
> Ah, did you actually disable HT in the BIOS, or just skip the HT
> enumeration by saying nr_cpus=64 (knowing that all the siblings are
> last)?

It's disabled in BIOS.

> In any case, Thomas has a clue and I'm going to test, but 4 socket
> machine takes forever to boot, so might be a few minutes :/

His one-liner made my DL980 all better.

	-Mike