lkml.org 
[lkml]   [2008]   [Nov]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 30 of 38] xen: implement io_apic_ops
    Ingo Molnar wrote:
    > * Jeremy Fitzhardinge <jeremy@goop.org> wrote:
    >
    >
    >> Writes to the IO APIC are paravirtualized via hypercalls, so implement
    >> the appropriate operations.
    >>
    >> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
    >> ---
    >> arch/x86/xen/Makefile | 3 +-
    >> arch/x86/xen/apic.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++
    >> arch/x86/xen/enlighten.c | 2 +
    >> arch/x86/xen/xen-ops.h | 2 +
    >> 4 files changed, 72 insertions(+), 1 deletion(-)
    >>
    >
    > hm, why is the ioapic used as the API here, and not an irqchip?
    >

    In essence, the purpose of the series is to break the 1:1 relationship
    between Linux irqs and hardware GSIs. This allows me to have my own irq
    allocator, which in turn allows me to intermix "physical" irqs (ie, a
    Linux irq number bound to a real hardware interrupt source) with the
    various software/virtual irqs the Xen system needs.

    Once a physical irq has been mapped onto a gsi interrupt source, the
    mechanisms for handing the ioapic side of things are more or less the
    same. There's the same procedure of finding the ioapic/pin for a gsi
    and programming the appropriate vector.

    (Presumably once I implement MSI support, all references to "gsi" will
    become "gsi/msi/etc".)

    So, there's an awkward tradeoff. I could just completely duplicate the
    whole irq/vector/ioapic management code and hide it under my own
    irqchip, but it would end up duplicating a lot of the existing code. My
    alternative was to try to open out the existing code into something like
    a thin ioapic library, which I can call into as needed. The only
    low-level difference is that the Xen ioapics need to be programmed via a
    hypercall rather than register writes.

    If the x86 interrupt layer in general decouples irqs from GSIs, then I
    can probably make use of that to clean things up. A general irq
    allocator along with some way of attaching interrupt-source-specific
    information to each irq would get me a long way, I think. I'd still
    need hooks to paravirtualize the actual ioapic writes, but at least I
    wouldn't need to have quite so much delicate hooking.

    Thanks,
    J


    \
     
     \ /
      Last update: 2008-11-20 18:03    [W:2.888 / U:0.800 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site