From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43899) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XmgDj-0008CK-2J for qemu-devel@nongnu.org; Fri, 07 Nov 2014 04:52:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XmgDc-0002Nq-Tm for qemu-devel@nongnu.org; Fri, 07 Nov 2014 04:52:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:42314) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XmgDc-0002NR-Kt for qemu-devel@nongnu.org; Fri, 07 Nov 2014 04:52:36 -0500 Received: from int-mx13.intmail.prod.int.phx2.redhat.com (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id sA79qZKP018697 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Fri, 7 Nov 2014 04:52:36 -0500 Date: Fri, 7 Nov 2014 10:52:31 +0100 From: Andrew Jones Message-ID: <20141107095230.GA6518@hawk.usersys.redhat.com> References: <1415290175-17314-1-git-send-email-drjones@redhat.com> <545BF212.2090404@redhat.com> <20141107092935.GB3004@hawk.usersys.redhat.com> <545C937E.6020106@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <545C937E.6020106@redhat.com> Subject: Re: [Qemu-devel] [PATCH] vl: rework smp_parse List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: qemu-devel@nongnu.org, ehabkost@redhat.com On Fri, Nov 07, 2014 at 10:40:14AM +0100, Paolo Bonzini wrote: > > > On 07/11/2014 10:29, Andrew Jones wrote: > >> > I think this would cause too many failures in the wild. Perhaps error > >> > out if it is lower, and warn if sockets * cores * threads > max_cpus > >> > since we actually allow hot-plug a thread at a time? > > We'd still have more failures if we choose to error out when it's lower, > > since we currently silently adjust threads in some of those cases, or > > just don't care that the topology doesn't support up to maxcpus in other. > > So I guess we need a decent fallback if it doesn't match. Something > like (based also on the reply from Eduardo): > > 1) always warn if max_cpus % (cores*threads) != 0 || smp_cpus % > (cores*threads) != 0 > > 2) if sockets*cpus*threads < max_cpus, adjust sockets to > DIV_ROUND_UP(max_cpus, cores*threads). If we didn't warn in step 1, do > it now. Give a different, less harsh warning if the cmdline > sockets*cpus*threads did match smp_cpus. In the latter case, the user > _almost_ knows what he was doing. > > Not perfect, but it could be something to start from. Adjusting sockets > is better than adjusting threads. OK. I can whip up a v2 that is less harsh (more warnings, less aborts). I'll also address the other issue I mentioned in the bottom of my reply to Eduardo, which is to make sure we consider machine_class->max_cpus. drew > > Paolo > > > I'm not sure how best to go about modifying the command line semantics > > in a backwards compatible way, other than to just create a new "-smp" > > option. I'm open to all opinions and suggestions.