From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38564) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cJpoW-0002nR-C6 for qemu-devel@nongnu.org; Wed, 21 Dec 2016 17:56:49 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cJpoT-0007wa-9k for qemu-devel@nongnu.org; Wed, 21 Dec 2016 17:56:48 -0500 Date: Thu, 22 Dec 2016 09:43:26 +1100 From: David Gibson Message-ID: <20161221224326.GB14282@umbus.fritz.box> References: <20161215061128.30792-1-david@gibson.dropbear.id.au> <1482160529.3732.2.camel@redhat.com> <20161219234717.GG23176@umbus.fritz.box> <1482225561.3732.12.camel@redhat.com> <20161221045245.GE13024@umbus.fritz.box> <1482309497.3732.30.camel@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="3lcZGd9BuhuYXNfi" Content-Disposition: inline In-Reply-To: <1482309497.3732.30.camel@redhat.com> Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCHv3 for-2.9 0/6] HPT resizing for pseries guests (qemu part) List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Andrea Bolognani Cc: paulus@samba.org, sjitindarsingh@gmail.com, lvivier@redhat.com, thuth@redhat.com, mdroth@linux.vnet.ibm.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org --3lcZGd9BuhuYXNfi Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Dec 21, 2016 at 09:38:17AM +0100, Andrea Bolognani wrote: > On Wed, 2016-12-21 at 15:52 +1100, David Gibson wrote: > > > > I'm not sure if we need a knob.=A0=A0I think in general enabling for > > > > pseries-2.9 and later machine types is correct.=A0=A0The difficulty= is > > > > that for HV guests, we can only enable it if the host kernel also h= as > > > > support.=A0=A0Explicitly setting "resize-hpt=3Denable" means qemu w= ill not > > > > start if the kernel doesn't support it. > > >=A0 > > > I thought that would be the case for resize-hpt=3Drequired, > > > not resized-hpt=3Denabled. > >=A0 > > resize-hpt=3Denabled requires the host to support resizing, but not the > > guest.=A0=A0resize-hpt=3Drequired requires both the host and the guest = to > > support resizing. > >=A0 > > If you can think of a less ambiguous word for it, let me know. >=20 > The name makes sense, we just need to document the host > kernel requirement properly. The error message should of > course mention it as well. The error message is currently "Hash page table resizing not available with this KVM version" Does that cover it? > > > Moreover, do you foresee any situation in which users > > > might reasonably want to turn the feature off even though > > > the entire stack (host kernel, QEMU, guest kernel) > > > understands it? > >=A0 > > Nothing clearly compelling.=A0=A0In the nearish term, being able to turn > > it off to isolate possible bugs could be useful of course.=A0=A0It's al= so > > possible that you could have a VM where the latency of each resize > > could be too much downtime - although in that case I doubt you'd want > > to hotplug memory anyway. >=20 > It seems like the use case would be fairly narrow, if it > existed at all. Given that, I think we should avoid adding > yet another knob to libvirt until its value can be > unquestionably proven. I tend to agree. --=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 --3lcZGd9BuhuYXNfi Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJYWwWOAAoJEGw4ysog2bOS90MQALyhduEPiPtxlk1tfrTVIjcT uicIStlzd+nCHawVaENMdrAzfMfblCweU6jalCnjQeq8+38thSqHy49oXVtf3S0B DkYwnPOZXVIvzxTLbE7o6Cz+uMgqLjywoaubgfHqJpTVHhy5pyNqsVYeXYvk5XHP BcZVpXJWeCm6gf/uQQ3jhqsbda3dTc9jEHZVb9Va6ocvcL8gH0vZsIqqvCG3jsNr iKTFy33ka5/8e0nMymWrlnmDFJZJKGteHgtkQHeWO8nl3wbgZVX5JZXjmpdN5aSm BAHVj4twt1n9Lw7ryvAnA30oA9TlRXgJNrO0QanBiskvxssBTUJxu2gi52jICpGb gQiezafeD27q1EInqpDI78MwytMlgUmkr+UtlRnIEKzZ/fcKuyZd/46alUJ6ikZd Kb3EpVefYIr0sglhFzeuaMkm77akN3ef3Vd94huBE9Zz+GSShx7pWu11PCGPUZTz whIF1DaFNnqfD5dlewSy1TR4jtmEZBxW1Hfki7WQv7iEwiHKjmhSh35J/yOMld/E EXFjyLGvAaYx4YNF0x9f6NdY/CIx5qjqslen3RiYKh2OHqrurSizHFynbdurreRl 7suvvuHQyzKSJFT/JyZKh40Dx8q1iZANx9uX2VHYaE6cMYKg0qmYtRwxPhdOGwDj s3crfmPmNjfhQVoGnFSJ =e6bi -----END PGP SIGNATURE----- --3lcZGd9BuhuYXNfi--