Question about apic ipi interface

[Stefan Bader <stefan.bader@canonical.com>]

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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.

Thanks,
Stefan


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