From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55975) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cCfJD-0008KK-DY for qemu-devel@nongnu.org; Thu, 01 Dec 2016 23:18:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cCfJC-0007El-9x for qemu-devel@nongnu.org; Thu, 01 Dec 2016 23:18:51 -0500 Date: Fri, 2 Dec 2016 14:37:41 +1100 From: David Gibson Message-ID: <20161202033741.GE10089@umbus.fritz.box> References: <20161101024634.GA14860@umbus.fritz.box> <1479218565.3319.18.camel@redhat.com> <3353ecef-2308-13e3-025d-df41b2e89945@ozlabs.ru> <1479457042.1391.11.camel@redhat.com> <1479733731.4367.4.camel@redhat.com> <98244c30-1397-5a1b-eb9a-446f41e9890e@ozlabs.ru> <20161123050214.GE17795@umbus.fritz.box> <1480084585.4367.69.camel@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="vv4Sf/kQfcwinyKX" Content-Disposition: inline In-Reply-To: <1480084585.4367.69.camel@redhat.com> Subject: Re: [Qemu-devel] [Qemu-ppc] [RFC PATCH qemu] spapr_pci: Create PCI-express root bus by default List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Bolognani Cc: Alexey Kardashevskiy , Greg Kurz , Paolo Bonzini , Alex Williamson , qemu-ppc@nongnu.org, qemu-devel@nongnu.org, libvir-list@redhat.com, Michael Roth --vv4Sf/kQfcwinyKX Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Nov 25, 2016 at 03:36:25PM +0100, Andrea Bolognani wrote: > On Wed, 2016-11-23 at 16:02 +1100, David Gibson wrote: > > > > The change from OHCI to XHCI only affected the *default* USB > > > > controller, which libvirt tries its best not to use anyway: > > > > instead, it will prefer to use '-M ...,usb=3Doff' along with > > > > '-device ...' and set both the controller model and its PCI > > > > address explicitly, partially to shield its users from such > > > > changes in QEMU. > > >=A0 > > > Ok. Always likes this approach really. We should start moving to this > > > direction with PHB - stop adding the default PHB at all when -nodefau= lts is > > > passed (or -machine pseries,pci=3Doff ?) and let libvirt manage PHBs = itself > > > (and provide another spapr-phb type like spapr-pcie-host-bridge or ad= d a > > > "pcie_root_bus_type" property to the existing PHB type). > > >=A0 > > > What will be wrong with this approach? > >=A0 > > Hm, that's a good point.=A0=A0If were removing the default PHB entirely, > > that I would consider a possible case for a new machine type.=A0=A0Putt= ing > > construction of the PHBs into libvirt's hand could make life simpler > > there.=A0=A0Although it would make it a bit of a pain for people starti= ng > > qemu by hand. > >=A0 > > I think this option is worth some thought. >=20 > Note that libvirt always runs QEMU with -nodefaults, so we > could just remove the default PHB if that flag is present, > and leave it in if that's not the case. >=20 > The idea itself sounds good, but of course it will require > more work from the libvirt side than simply making the PCIe > machine type behave like q35 and mach-virt. Yeah, but the latter basically just won't work. > Moreover, we already have an RFE for supporting additional > PHBs, we could solve both issues in one fell swoop and have > the libvirt guest XML be a more faithful representation of > the actual virtual hardware, which is always a win in my > book. Right. And the general recomendation for PAPR guests is that each passed through device (or rather, each passed through iommu group) have a separate virtual PHB on the guest. With this rework libvirt could switch over to implementing that recommendation. > That will be even more important if it turns out that the > rules for PCIe device assignment (eg. what device/controller > can be plugged into which slot) are different for PCIe PHBs > than they are for q35/mach-virt PCIe Root Bus. I've asked > for clarifications about this elsewhere in the thread. >=20 > --=A0 > Andrea Bolognani / Red Hat / Virtualization >=20 --=20 David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson --vv4Sf/kQfcwinyKX Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJYQOyDAAoJEGw4ysog2bOSOpAP/34fEJXZvg+BVZP6Jw8YY1iJ WT7c1hyWDTKvQPFt3JGEy7nJfEwM4Kw+xiYbaI/cJP9Q4SVJlH6RXj472lr7Mq2O 1LEcJBwgnqlIs6e4vHsAYB14QFM5K2m8olonn+VIvdqBeDQhbjH0K5Ivfjz0U40x FjmUM5N9pc8+/nWIqNUIrF9Hd5giCzG2Jl4PJLy/7m4LmpuqH+ybTIWZ+QhiLo0w PK+ULRzrGT/mL7eKTKcPSuXSsy5mWW4GtQ8OwpZstTQccTnhaHvf2IsNoSuXR3iy Gdam0caSN/4YbNi7b9UmKT96VxbG2i2bW0/nArf7PPjWvI4010/azdxBLg2rcyFB ijVk0MbPU1Fr2gKzmg1RSZfJ108wC/3FP47BCSr6UPsEjC3cemVPMfyx+wW4ypyH hYO4GGozufFXtB6vXr5ISvD0/ifqAZB/8J7R00/DcNVFIpEdLicZTWmgiYrxicnU tt93k/PjC3MMe4K215jo1z/+rXcCwKw8q3+UG+aMYnGfoyMaomZx5avdrYa6WcRs yBmzu4mDriq8Gozq9+s7YDKj+O41TjDXo0keuxP9Jwq7befY2SnUZXRdUA1WSB3w 0rvCll6H6D33WvM9BZmU5hiywseNI73nEXjocDt/qWvJFNhLCeLjWBPhIViGtP39 gPG2Tscc82BRkvNDnGtC =870f -----END PGP SIGNATURE----- --vv4Sf/kQfcwinyKX--