From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44508) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cS4jN-0000p0-1n for qemu-devel@nongnu.org; Fri, 13 Jan 2017 11:29:33 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cS4jI-0004Aw-5E for qemu-devel@nongnu.org; Fri, 13 Jan 2017 11:29:33 -0500 Received: from 11.mo1.mail-out.ovh.net ([188.165.48.29]:57346) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cS4jH-00049B-Vd for qemu-devel@nongnu.org; Fri, 13 Jan 2017 11:29:28 -0500 Received: from player726.ha.ovh.net (b7.ovh.net [213.186.33.57]) by mo1.mail-out.ovh.net (Postfix) with ESMTP id 00E5238602 for ; Fri, 13 Jan 2017 17:29:16 +0100 (CET) Date: Fri, 13 Jan 2017 17:29:00 +0100 From: Greg Kurz Message-ID: <20170113172900.2575cc19@bahia.lan> In-Reply-To: <20170112225736.GB13656@umbus.fritz.box> References: <20170105054618.GA12106@umbus.fritz.box> <1483724069.4199.80.camel@redhat.com> <20170108234621.GB12515@umbus.fritz.box> <1484217095.7948.1.camel@redhat.com> <20170112225736.GB13656@umbus.fritz.box> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/EjNoJOXp.8/gnjCm3uHpd3p"; protocol="application/pgp-signature" Subject: Re: [Qemu-devel] Proposal PCI/PCIe device placement on PAPR guests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: David Gibson Cc: Andrea Bolognani , thuth@redhat.com, lvivier@redhat.com, benh@kernel.crashing.org, marcel@redhat.com, aik@ozlabs.ru, ehabkost@redhat.com, mdroth@linux.vnet.ibm.com, libvir-list@redhat.com, qemu-devel@nongnu.org, qemu-ppc@nongnu.org, laine@redhat.com --Sig_/EjNoJOXp.8/gnjCm3uHpd3p Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 13 Jan 2017 09:57:36 +1100 David Gibson wrote: > On Thu, Jan 12, 2017 at 11:31:35AM +0100, Andrea Bolognani wrote: > > On Mon, 2017-01-09 at 10:46 +1100, David Gibson wrote: =20 > > > > >=C2=A0=C2=A0=C2=A0=C2=A0* To allow for hotplugged devices, libvirt= should also add a number > > > > >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0of additional, empty vPHBs (th= e PAPR spec allows for hotplug of > > > > >=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0PHBs, but this is not yet impl= emented in qemu). =20 > > > >=C2=A0 > > > > "A number" here will have to mean "one", same number of > > > > empty PCIe Root Ports libvirt will add to a newly-defined > > > > q35 guest. =20 > > >=C2=A0 > > > Umm.. why? =20 > >=20 > > Because some applications using libvirt would inevitably > > start relying on the fact that such spare PHBs are > > available, locking us into providing at least the same > > number forever. In other words, increasing the amount at > > a later time is always possible, but decreasing it isn't. > > We did the same when we started automatically adding PCIe > > Root Ports to q35 machines. > >=20 > > The rationale is that having a single spare hotpluggable > > slot is extremely convenient for basic usage, eg. a simple > > guest created by someone who's not necessarily very > > familiar with virtualization; on the other hand, if you > > are actually deploying in production you ought to conduct > > proper capacity planning and figure out in advance how > > many devices you're likely to need to hotplug throughout > > the guest's life. =20 >=20 > Hm, ok. Well I guess the limitation is the same as on x86, so it > shouldn't surprise people. >=20 > > Of course this all will be moot once we can hotplug PHBs :) =20 >=20 > Yes. Unfortunately, nobody's actually working on that at present. >=20 Well, there might be someone now :) Michael Roth had posted a RFC patchset back in 2015: https://lists.gnu.org/archive/html/qemu-ppc/2015-04/msg00275.html I'll start from here. Cheers. -- Greg --Sig_/EjNoJOXp.8/gnjCm3uHpd3p Content-Type: application/pgp-signature Content-Description: OpenPGP digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iEYEARECAAYFAlh5AEwACgkQAvw66wEB28IY4gCaA/LcdhBMkUABmcUuzFtF+jdh 6fQAoI3ndmPEKOnxHe5z6zSaaZa5RHWX =W+73 -----END PGP SIGNATURE----- --Sig_/EjNoJOXp.8/gnjCm3uHpd3p--