From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52959) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VIuUl-0003JF-5e for qemu-devel@nongnu.org; Mon, 09 Sep 2013 01:58:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1VIuUe-0001WC-3f for qemu-devel@nongnu.org; Mon, 09 Sep 2013 01:58:43 -0400 Received: from mail-pa0-f49.google.com ([209.85.220.49]:49525) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1VIuUd-0001W0-Tk for qemu-devel@nongnu.org; Mon, 09 Sep 2013 01:58:36 -0400 Received: by mail-pa0-f49.google.com with SMTP id ld10so5812765pab.36 for ; Sun, 08 Sep 2013 22:58:34 -0700 (PDT) Message-ID: <522D6383.8050700@ozlabs.ru> Date: Mon, 09 Sep 2013 15:58:27 +1000 From: Alexey Kardashevskiy MIME-Version: 1.0 References: <1378193502-4968-1-git-send-email-aik@ozlabs.ru> <20130905043059.GC10158@voom.redhat.com> <52280E96.1030402@ozlabs.ru> <350E3728-BF3A-4B43-8E43-2622033970D0@suse.de> <52285369.1040907@ozlabs.ru> <1378381449.4321.158.camel@pasglop> <1378388164.4321.176.camel@pasglop> <17161D2C-8CAE-40D9-B4E2-EBCE69D69FAA@suse.de> <522891C2.8020107@suse.de> <1378391219.4321.191.camel@pasglop> <522D3534.6070207@ozlabs.ru> <2D3C9633-E8AE-4290-910A-5656E19B02A6@suse.de> In-Reply-To: <2D3C9633-E8AE-4290-910A-5656E19B02A6@suse.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [RFC PATCH] spapr: support time base offset migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: "qemu-devel@nongnu.org" , "qemu-ppc@nongnu.org" , Paolo Bonzini , Paul Mackerras , =?UTF-8?B?QW5kcmVh?= =?UTF-8?B?cyBGw6RyYmVy?= , David Gibson On 09/09/2013 03:50 PM, Alexander Graf wrote: > > > Am 09.09.2013 um 04:40 schrieb Alexey Kardashevskiy : > >> On 09/06/2013 01:11 AM, Alexander Graf wrote: >>> >>> On 05.09.2013, at 16:26, Benjamin Herrenschmidt wrote: >>> >>>> On Thu, 2013-09-05 at 16:14 +0200, Andreas Färber wrote: >>>> >>>>> Are you thinking of POWER8 having a different frequency than POWER8 in >>>>> compat mode? Because migration from one -cpu to another is not supported >>>>> elsewhere. >>>>> >>>>> Even if we want to migrate from one POWER7 revision to another, we >>>>> should let the destination use the revision of the source (guest ABI!), >>>>> via property if need be. Anything else will lead to confusion as to what >>>>> is supported and what is not. That -cpu host is the default for >>>>> convenience shouldn't relieve admins/libvirt to think about sensible >>>>> setups like they have to on x86. >>>> >>>> Besides POWER8 uses 512Mhz too :-) It's been architected so it's >>>> unlikely to change from now on. >>> >>> Ok, ditch the tb frequency then. We can always default to 512Mhz when it's absent. >> >> >> QEMU uses what kvmppc_get_tbfreq() returns. And ppc_tb_t carries this >> value. It does not use 512MHz automatically but migration should always >> assume 512MHz :-/ >> >> If we remove it, I would like to add assert(tb_freq!=512MHz) into >> timebase_pre_save() and timebase_post_load(), is that ok? > > Good point. This would break TCG migration, right? In TCG we do not need any timebase offset at all, the time should migrate as is, no? :) It could break something like power5 migration under PR KVM, do not know... -- Alexey