From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49519) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZZqtA-00037d-Vq for qemu-devel@nongnu.org; Wed, 09 Sep 2015 21:43:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZZqss-0002oJ-SU for qemu-devel@nongnu.org; Wed, 09 Sep 2015 21:43:00 -0400 Date: Thu, 10 Sep 2015 11:24:46 +1000 From: David Gibson Message-ID: <20150910012446.GG17641@voom.redhat.com> References: <1441761736-32030-1-git-send-email-david@gibson.dropbear.id.au> <55EFD0DE.1050001@redhat.com> <20150909071934.GD17641@voom.redhat.com> <55EFDFCE.2040609@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="oXNgvKVxGWJ0RPMJ" Content-Disposition: inline In-Reply-To: <55EFDFCE.2040609@redhat.com> Subject: Re: [Qemu-devel] [PATCH] spapr: Reduce advertised max LUNs for spapr_vscsi List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Thomas Huth Cc: lvivier@redhat.com, pbonzini@redhat.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org --oXNgvKVxGWJ0RPMJ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Sep 09, 2015 at 09:29:18AM +0200, Thomas Huth wrote: > On 09/09/15 09:19, David Gibson wrote: > > On Wed, Sep 09, 2015 at 08:25:34AM +0200, Thomas Huth wrote: > >> On 09/09/15 03:22, David Gibson wrote: > >>> The implementation of the PAPR paravirtual SCSI adapter currently > >>> allows up to 32 LUNs (max_lun =3D=3D 31). However the adapter isn't = really > >>> designed to support lots of devices - the PowerVM implementation only > >>> ever puts one disk per vSCSI controller. > >> > >> Do you know how many LUNs are advertised by PowerVM? > >=20 > > Well, what do you mean by "advertised". AFAIK from the point of view > > of the guest, the number of LUNs is advertised per-target, not per > > controller. >=20 > I mean, what's the highest LUN number that can be seen by a guest under > PowerVM? Is it always using only one LUN per controller, or is there a > way to change the amount of LUNs? (Sorry if I ask dumb questions ... I > do not have much experience with PowerVM yet) Um.. I'm not sure, I have very little experience with PowerVM too. I think with PowerVM it's usually real SCSI devices being passed through, rather than disk images, so presumably the SCSI target itself reports however many LUNs it has. There may be a limitation in PowerVM, or in the AIX VIO server I think it typically backends onto, but I don't know what it is. Since that limit has been in the guest side driver forever, presumbly no-one has hit LUNs > 8 in practice. > >>> More specifically, the Linux guest side vscsi driver (the only one we > >>> really care about) is hardcoded to allow a maximum of 8 LUNs. > >> > >> So what about changing the vscsi driver in Linux instead to support mo= re > >> LUNs? > >=20 > > Doesn't help for existing guests. Basically what I'm trying to > > achieve is for qemu to reject up-front configurations that are > > unlikely to actually work in the guest. >=20 > I just wonder whether it makes sense to change the guest instead. In the > future, if we ever have guests that support more LUNs than 8 (maybe some > non-Linux guests like FreeBSD?), we've got to change QEMU back again... > OTOH, since this is just a one-line fix, it's likely ok to limit this to > 8 now - it's easy to revert if we ever need to, so I'm fine with that > change, I just wanted to discuss the other possibilites. Remember that the spapr-vscsi device exists pretty much entirely to make transition simpler for existing PowerVM guests. New guests (Linux or otherwise) intended to run under KVM should be using virtio-blk or virtio-scsi. --=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 --oXNgvKVxGWJ0RPMJ Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQIcBAEBAgAGBQJV8NveAAoJEGw4ysog2bOSjWUQAMMNjYC400PfFgjGFp49gf72 OHqP2dYmqwZNdnNiHg+L3gTZyeTyW4ufAQtpZd3n1U3a3ZBuFb849kbJ/yMna46n 9gAi6ZP8c9TB7wpfz1C236tJ8bjiUZoaFSJDrUN9V/ABd/GrPNbslREvXTunvCSk 5l5K1aoVeDcusOK3Mv/A2e4q1fmmQBmRRezIAn+jdtC+cXibsOLjVVlKVLoIJKhn lSJLDvtEfEzE1cSLvmqVPYyKDpIEsz2JBnhmHOAHXMQ8iLD7pKfD1TXWwytAbGMD nPet1E8eKCP1LN1M9qStSythp71EUaKBKP+EtsnmIYs1h8jId2yTBrvdhJkaLch8 G2qAbmiS8iUR/D/KLH5HQ4DwuhGXkmgHa6fX2UNrlStMeMrUV/6ZBpR1wZeT6Wsb tEOUt9/ThDBcbxfd+/ZRgeW2qd6K1miEIZ/CG6xc1xF+bOjOrrX8/l1B69euuxBq 2wVX9nA6JyDnjstkwV16nMPOvP3aCmUox+3ByBjBdvrkKlch4a8/EyYy3ot6qsvF 8eYGJX1LjVzz0iW7DiS+aIq6P2nczlPTLJuoQn7A3ym+PDcn5qyzbBzPZohvJxUC 6oN87NK+bwbOvkAJHIaWZaAtqhykS4fjz/MtlTwtiszSEYON0xR3Gk+LuChqtkPE tzaORVPzeKJ7IZ5Frh97 =jCW5 -----END PGP SIGNATURE----- --oXNgvKVxGWJ0RPMJ--