Re: [Xen-devel] Question about apic ipi interface

[Ben Guthro <ben@xxxxxxxxxx>]

On Tue, Apr 23, 2013 at 11:07 AM, Stefan Bader
<stefan.bader@xxxxxxxxxxxxx> wrote:
> I was looking at some older patch and there is one thing I do not understand.
>
> commit f447d56d36af18c5104ff29dcb1327c0c0ac3634
>     xen: implement apic ipi interface
>
> Specifically there the implementation of xen_send_IPI_mask_allbutself().
>
> void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
>                                 int vector)
> {
>         unsigned cpu;
>         unsigned int this_cpu = smp_processor_id();
>
>         if (!(num_online_cpus() > 1))
>                 return;
>
>         for_each_cpu_and(cpu, mask, cpu_online_mask) {
>                 if (this_cpu == cpu)
>                         continue;
>
>                 xen_smp_send_call_function_single_ipi(cpu);
>         }
> }
>
> Why is this using xen_smp_send_call_function_single_ipi()? This dumps the
> supplied vector and always uses XEN_CALL_FUNCTION_SINGLE_VECTOR. In contrast 
> the
> xen_send_IPI_all() and xen_send_IPI_self() keep the (mapped) vector.
>
> Mildly wondering about whether call function would need special casing (just
> because xen_smp_send_call_function_ipi() is special). But I don't have the big
> picture there.
>

Adding Lin Ming here, since this was an evolution of an incomplete
implementation of mine that was
ultimately used in a larger context, outside of my original use case
for it (kgdb of dom0) that ultimately
gave me credit for this part of the patch, as part of a larger series.

I must admit that I don't recall the reasoning, if there was one.
It may be an oversight.

This was the original (incomplete) patch, in context:
http://markmail.org/message/d6ca5zfdmiqipurt


Are you seeing issues with the code, or just doing code inspection?

Ben

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