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

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

On 23.04.2013 14:15, Ben Guthro wrote:
> 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?

No issues, I was just looking at the patch because we were asked to backport it
to fix another issue (access to the apic IPI functions without checking whether
there is a pointer). Since things did work in most cases before, maybe there is
no real usage. :) I was just curious.

Stefan

> 
> Ben
>

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