On Fri, May 04, 2018 at 04:25:16PM +0200, Cédric Le Goater wrote: > On 04/27/2018 04:43 AM, David Gibson wrote: > >>>> I did some work on that topic a while ago : > >>>> > >>>> https://patchwork.ozlabs.org/cover/836782/ > >>>> > >>>> But we stopped exploring the idea. May be it was not the good approach. > >>>> The PHBs LSIs would benefit from such a split though. > >>> So, no, I don't think that was a good approach, but that doesn't mean > >>> other ways of rearranging the irq numbers aren't ok. The thing here > >>> is that we don't want to think of an "irq allocator" - there are some > >>> bits like that in there already, but they were always a mistake. > >>> > >>> We have lots of irq space (both XICS and XIVE) so instead we should > >>> come up with a static mapping of irqs to devices. > >> yes. I would prefer that also. > >> > >> We could change the spapr_irq_alloc() routine to get a block of > >> IRQs in the range defined for a device family, and use a device > >> id to offset in that family range ? Here are some figures : > >> > >> device family block size max devices > >> > >> EVENT_CLASS_EPOW 1 1 > >> EVENT_CLASS_HOT_PLUG 1 1 > >> VIO_VSCSI 1 10 > >> VIO_LLAN 1 10 > >> VIO_VTY 1 5 > >> > >> PCI/PHB 1024 5 > > No, I'm thinking we should eliminate spapr_irq_alloc() entirely. > > Well, ok, not entirely, we'll still need it for the old machine > > types. But remove it's use for the current machine type completely. > > > > Instead we have an explicit map of ranges for various purposes. The > > one-off things like EPOW and HOTPLUG can have plain constant values. > > PCI LSIs will be calculated as something like PCI_IRQ_BASE + <phb > > index>*4 + <irq pin>. The VIO devices we handle as VIO_BASE + <reg > > value> or something. > > > > MSIs will still need some sort of allocation, but we can do that > > within a range set aside for them. > > Should we address the static mapping of irqs before introducing XIVE ?
Yes, I think so.
> I don't think it changes much of the architecture now that the allocator
> is under the machine. However, I wonder what would be the impact of
> PHB hotplug.
I don't think it should be too bad. We now require that PHBs have the
'index' parameter set, and that won't change with hotplug. We can
then set aside a region of irq #s for each index of PHB.
--
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
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