From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35205) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZZv6S-0003Ab-5A for qemu-devel@nongnu.org; Thu, 10 Sep 2015 02:13:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZZv6N-0003Pj-0q for qemu-devel@nongnu.org; Thu, 10 Sep 2015 02:13:00 -0400 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> <20150910012446.GG17641@voom.redhat.com> From: Thomas Huth Message-ID: <55F11F5F.9040209@redhat.com> Date: Thu, 10 Sep 2015 08:12:47 +0200 MIME-Version: 1.0 In-Reply-To: <20150910012446.GG17641@voom.redhat.com> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="jtc268aUMsPU1cjn2FFGaXjLSC98JmJcX" 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: David Gibson Cc: lvivier@redhat.com, pbonzini@redhat.com, qemu-ppc@nongnu.org, qemu-devel@nongnu.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --jtc268aUMsPU1cjn2FFGaXjLSC98JmJcX Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 10/09/15 03:24, David Gibson wrote: > 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 on= ly >>>>> ever puts one disk per vSCSI controller. >>>> >>>> Do you know how many LUNs are advertised by PowerVM? >>> >>> 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. >> >> I mean, what's the highest LUN number that can be seen by a guest unde= r >> 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) >=20 > 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. >=20 > Since that limit has been in the guest side driver forever, presumbly > no-one has hit LUNs > 8 in practice. >=20 >>>>> 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 = more >>>> LUNs? >>> >>> 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. >> >> I just wonder whether it makes sense to change the guest instead. In t= he >> future, if we ever have guests that support more LUNs than 8 (maybe so= me >> non-Linux guests like FreeBSD?), we've got to change QEMU back again..= =2E >> 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. >=20 > 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. FWIW, I had a quick look at FreeBSD sources here: https://svnweb.freebsd.org/base/stable/10/sys/powerpc/pseries/phyp_vscsi.= c?revision=3D259204&view=3Dmarkup =2E.. and as far as I can see, they do not limit the LUNs to 8. (I only spotted a "cpi->max_lun =3D ~(lun_id_t)(0);" in there). So there indeed might also be older guests that support more than 8 LUNs.= Thomas --jtc268aUMsPU1cjn2FFGaXjLSC98JmJcX Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQIcBAEBAgAGBQJV8R9fAAoJEC7Z13T+cC21CQcP/0wGfQ7haTkDek1AzgmaJsZb jU01QmGni7dGWZ3hWQi/94XI2JIViBcRrd5sbkpYq3zrkE0fLM2Yvn9yyoahPoEL 3/xjtPCz4Gexm3b2FrTdicl9vM7MClkC/NHFh+RUb/Ya90i0A9qfKzozAEOdZFhO ISvBuQkrNFbvsqQZ3vakfF/RlzBZ1HAc1XYvkD2EZWOxaCp8cUujZ/azpiO2B097 osZuElxLi7zOC+MdoeHy1x+XqfEb+klLG/XBCZiiLF9NDsG5dolwPB2ud+i01gf3 O0yTVRRQcxYvyeEoKes9taNDrK+Cjw6/70kj3o7N12T8OUAUlYAXKD6cca95m49Z qXXWuZp0H/pHwSBX2sUWM5dYvGm6+ybEv7XLfODeMYWnPyRmlHoVpM2M6QFJwz/P SYJiAokECTtP1x3PKETPtW/P5HyNSapocSJ57b32+hbAKf35s1B+BL2bvdL8OJDE kh5aq9WqLxtqQkCTll47tGCoqCF3eczHH+VALbT8pj0Blf80x+GHgshp49xEEO94 v4hEaFiyrxuIjBtgFnYWk/N4ou9HW/vJ3m6lOZV9VOaprQh2ja7bSyWTwzFt7ysO qmIo5SiLZMbIYhhCJyni7hr6mYpba0dh3qz3ZCcjqaSTR5fM0mTjDydLVhnetU0O xXUcHIC2s3YRGds62N8h =ov2s -----END PGP SIGNATURE----- --jtc268aUMsPU1cjn2FFGaXjLSC98JmJcX--