From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756996AbcCRKQe (ORCPT ); Fri, 18 Mar 2016 06:16:34 -0400 Received: from casper.infradead.org ([85.118.1.10]:57791 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753332AbcCRKQ0 (ORCPT ); Fri, 18 Mar 2016 06:16:26 -0400 Date: Fri, 18 Mar 2016 11:15:59 +0100 From: Peter Zijlstra To: Mike Galbraith Cc: Xiong Zhou , Thomas Gleixner , "linux-kernel@vger.kernel.org" , Ingo Molnar , Borislav Petkov , Andreas Herrmann Subject: Re: 4.5.0+ panic when setup loop device Message-ID: <20160318101559.GG6344@twins.programming.kicks-ass.net> References: <20160317095220.GO6344@twins.programming.kicks-ass.net> <1458274314.3859.25.camel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1458274314.3859.25.camel@gmail.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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)? 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 :/