[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification
From: |
David Gibson |
Subject: |
Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification |
Date: |
Fri, 16 Sep 2011 13:06:16 +1000 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Thu, Sep 15, 2011 at 09:01:38AM +0200, Paolo Bonzini wrote:
> On 09/15/2011 05:14 AM, David Gibson wrote:
> >Under PAPR, there is generally only
> >supposed to be one SCSI target (disk / cd / whatever) per virtual scsi
> >bus. But the generic qdev code will, by default, keep assigning
> >devices to the existing bus until it's full. Any thoughts on how to
> >sanely change that behaviour on a per-machine basis?
>
> You could change the if_max_devs array in blockdev.c to something
> provided by the machines.
>
> However, I'm not sure about this, for two reasons:
>
> 1) do you mean, in Linux terms, one target per SCSI _host_ or one
> target per SCSI _channel_? i.e. if you looks at
> /sys/bus/scsi/devices, right now it looks like
>
> 0:0:0:0 0:0:1:0 (two targets on the same host and channel)
>
> Should it be?
>
> 0:0:0:0 0:1:0:0 (one target per channel)
>
> or
>
> 0:0:0:0 1:0:0:0 (one target per host)
>
> If it is the former, then you are simply hitting a limitation of the
> SCSI layer in QEMU and I do have patches to make assignment more
> flexible. Based on the Linux VSCSI driver, and based on what SLOF
> does, I'd guess that's what you mean.
Well, now I'm confused. I had a look at a pHyp machine, and Linux
seemed to see it as multiple targets on a single channel, but I'm sure
the PAPR spec says you shouldn't have that. So I'm going to have to
look closer now.
> 2) does this matter at all? First, when doing "real world"
> virtualization you won't use the legacy options (neither -hda/-cdrom
> nor "-drive ...,if=scsi"), you would use -device to manually assign
> the devices to their buses.
Well, perhaps, but I really prefer to have sane defaults, rather than
having to build the machine myself on the command line.
> Second, why should you care in the case
> of SCSI? It seems like a very hard limitation to me, and unlike the
> PCI case it doesn't buy you anything in terms of isolation.
Ah, there is a good reason on this side. I forget the exact details,
but due to the protocol it uses there's some blocksize limit that is
only advertised per vscsi adaptor, whereas it should really be a
per-target quantity (and is different in practice for cdroms and
disks). Of course that's arguably a bug in the vscsi protocol, but we
can't fix that.
--
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
- Re: [Qemu-ppc] [PATCH 24/58] PPC: E500: Add PV spinning code, (continued)
[Qemu-ppc] [PATCH 53/58] openpic: Unfold read_IRQreg, Alexander Graf, 2011/09/14
[Qemu-ppc] [PATCH 02/58] spapr: prepare for qdevification of irq, Alexander Graf, 2011/09/14
[Qemu-ppc] [PATCH 27/58] device tree: dont fail operations, Alexander Graf, 2011/09/14
[Qemu-ppc] [PATCH 58/58] KVM: Update kernel headers, Alexander Graf, 2011/09/14
[Qemu-ppc] [PATCH 40/58] PPC: Fix sync instructions problem in SMP, Alexander Graf, 2011/09/14
[Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Alexander Graf, 2011/09/14
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, David Gibson, 2011/09/14
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Paolo Bonzini, 2011/09/15
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification,
David Gibson <=
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Paolo Bonzini, 2011/09/16
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Thomas Huth, 2011/09/16
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Paolo Bonzini, 2011/09/16
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Benjamin Herrenschmidt, 2011/09/16
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Thomas Huth, 2011/09/19
- Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Paolo Bonzini, 2011/09/19
Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, David Gibson, 2011/09/16
Re: [Qemu-ppc] [PATCH 01/58] spapr: proper qdevification, Paolo Bonzini, 2011/09/19
[Qemu-ppc] [PATCH 29/58] MPC8544DS: Remove CPU nodes, Alexander Graf, 2011/09/14
[Qemu-ppc] [PATCH 56/58] PPC: Fix via-cuda memory registration, Alexander Graf, 2011/09/14