From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marek =?utf-8?Q?Marczykowski-G=C3=B3recki?= Subject: Re: e820_host default value and libxl (not xl) Date: Mon, 23 May 2016 13:27:31 +0200 Message-ID: <20160523112731.GC25975@mail-itl> References: <20160521024211.GK1171@mail-itl> <20160523104748.GC31306@citrix.com> <5742E27E.2070400@citrix.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============4524554416499962926==" Return-path: In-Reply-To: <5742E27E.2070400@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xen.org Sender: "Xen-devel" To: Andrew Cooper Cc: Wei Liu , xen-devel List-Id: xen-devel@lists.xenproject.org --===============4524554416499962926== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ZyopXzg6HFtLX2Sw" Content-Disposition: inline --ZyopXzg6HFtLX2Sw Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, May 23, 2016 at 11:59:10AM +0100, Andrew Cooper wrote: > On 23/05/16 11:47, Wei Liu wrote: > > On Sat, May 21, 2016 at 04:42:11AM +0200, Marek Marczykowski-G=C3=B3rec= ki wrote: > >> Hi, > >> > >> According to xl.cfg(5) " This option defaults to true (1) if any PCI > >> passthrough devices are configured and false (0) otherwise." > >> And indeed this behaviour is implemented in xl. But not in libxl, which > >> means other libxl based toolstacks (libvirt) will not take advantage of > >> this directly. > >> > >> What would be the best approach here? Duplicate that behaviour in > >> libvirt (currently libvirt knows nothing about this option), or move > >> that default handling to libxl? I think the later makes more sense, but > >> maybe there is some reason against it? > >> > > The latter. > > > > I wouldn't be surprised if the boundary between xl and libxl was > > overlooked when implementing this flag. I've done similar things to push > > xsm label handling logic from xl to libxl. >=20 > Please don't propage this bandaid any further than it currently is. It > is not appropriate for libxl to set this by default. >=20 > The reason it is currently used is because libxl/libxc doesn't know how > to lay out a guests physmap. This is something I am working on > resolving for some ballooning issues we are having in XenServer. Does it mean e820_host wouldn't be needed anymore? > xl can get away defaulting this on, because xl is inherently a single > host toolstack. However, using host_e820 is wrong for any multi-host > setup where the VM might plausibly migrate (which includes the > passthrough case here). But *currently* having host_e820 disabled makes it impossible to passthrough some devices, even when no migration is involved. Libvirt does not support e820_host. So, I'm looking for a solution for the problem, which makes it impossible to use some devices at all when using libvirt. If e820_host will not be needed anymore in the near future, I can wait, or simply carry a local patch for this. But otherwise I think it would be good to fix this in either libxl or libvirt. --=20 Best Regards, Marek Marczykowski-G=C3=B3recki Invisible Things Lab A: Because it messes up the order in which people normally read text. Q: Why is top-posting such a bad thing? --ZyopXzg6HFtLX2Sw Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQEcBAEBCAAGBQJXQukiAAoJENuP0xzK19csw8QH/iy3pQoxWsiuCcqQYwkxJeEP pttOf8l6mOUrFYKr+ifqQLUD4iJx5D3iKoraRnmyEEBXAgh7yvTmgftzvyanyvsQ 6TrCsKrxQo48MbRo9KC0X0izd9w0Aq12yVIKfDP6AcSs4nGOrqDhRApENlcm1x16 XA759Lpoj3UrGQc3IarekGQm95K//ICEAX1Jcb+7axk1bHuKdq+J61H3kTEKWbK4 UVOLFp+LZ+/PfVQW1toJJwvQEZREl1oZGg8eYa3OPeqqTqdomidXc8aJEC9TceNq ufKoUorx5CaHlYkW2JoYc7Y671b+59BOJwTlxLgEPFG4loCkFNV2JB2Y1vqsM5c= =ISDV -----END PGP SIGNATURE----- --ZyopXzg6HFtLX2Sw-- --===============4524554416499962926== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Disposition: inline X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX18KWGVuLWRldmVs IG1haWxpbmcgbGlzdApYZW4tZGV2ZWxAbGlzdHMueGVuLm9yZwpodHRwOi8vbGlzdHMueGVuLm9y Zy94ZW4tZGV2ZWwK --===============4524554416499962926==--