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Re: [Xen-devel] IRQ SMP affinity problems in domU with vcpus > 4 on HP ProLiant G6 with dual Xeon 5540 (Nehalem)

On Mon, 2009-10-12 at 13:25 +0800, Cinco, Dante wrote:
> With vcpus < 4, logical flat mode works fine (no error message). I can
> change smp_affinity to any value > 0 and < 16 and the interrupts go to
> the proper CPU(s). Could you point me to the code that handles MSI so
> that I can better understand the MSI implementation?

There are two parts:
  1) init or changing the data and address of MSI:
    1) qemu-xen: hw/passthrough.c: pt_msg.*_write, MSI access are
                 trapped here first. And then pt_update_msi in
                 hw/pt-msi.c is called to update the MSI binding.
    2) xen:      drivers/passthrough/io.c: pt_irq_create_bind_vtd,
                 where MSI is actually bound to the guest.

  2) on MSI reception:
    In drivers/passthrough/io.c, hvm_do_IRQ_dpci and hvm_dirq_assist
    are the routines responsible for handling all assigned irqs
    (including MSI), and if an MSI is received, vmsi_deliver in
    arch/x86/vmsi.c get called to deliver MSI to the corresponding

And I just learned from Xiantao Zhang that for the guest Linux kernel,
it enables per-cpu vector if it's in physical mode, and that looks more
likely relevant to this problem. It had problem in the older xen to
handle this, and changeset 20253 is supposed to fix it, although I
noticed your xen version is 20270.


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