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

[Stefan Bader <stefan.bader@xxxxxxxxxxxxx>]

On 22.05.2013 21:40, Konrad Rzeszutek Wilk wrote:
> On Wed, May 08, 2013 at 06:26:40PM +0200, Stefan Bader wrote:
>> On 23.04.2013 12:07, Stefan Bader 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.
>>>
>>
>> This never got really answered, so lets try this: Does the following patch 
>> seem
>> to make sense? I know, it has not caused any obvious regressions but at least
>> this would look more in agreement with the other code. It has not blown up 
>> on a
>> normal boot either.
>> Ben, is there a simple way that I would trigger the problem you had?
>>
>> -Stefan
>>
>>
>> From e13703426f367c618f2984d376289b197a8c0402 Mon Sep 17 00:00:00 2001
>> From: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
>> Date: Wed, 8 May 2013 16:37:35 +0200
>> Subject: [PATCH] xen: Clean up apic ipi interface
>>
>> Commit f447d56d36af18c5104ff29dcb1327c0c0ac3634 introduced the
>> implementation of the PV apic ipi interface. But there were some
>> odd things (it seems none of which cause really any issue but
>> maybe they should be cleaned up anyway):
>>  - xen_send_IPI_mask_allbutself (and by that xen_send_IPI_allbutself)
>>    ignore the passed in vector and only use the CALL_FUNCTION_SINGLE
>>    vector. While xen_send_IPI_all and xen_send_IPI_mask use the vector.
>>  - physflat_send_IPI_allbutself is declared unnecessarily. It is never
>>    used.
>>
>> This patch tries to clean up those things.
>>
>> Signed-off-by: Stefan Bader <stefan.bader@xxxxxxxxxxxxx>
> 
> Looks very similar to 
> 
> https://patchwork.kernel.org/patch/2414311/
> 
> So two people pointing out the same thing. 

Yeah, from this discussion and further looking into it I am relatively sure this
has no visible effect either way because there currently is no user of the "odd"
implementations.

>> ---
>>  arch/x86/xen/smp.c |   10 ++++------
>>  arch/x86/xen/smp.h |    1 -
>>  2 files changed, 4 insertions(+), 7 deletions(-)
>> diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
>> index 8ff3799..fb44426 100644
>> --- a/arch/x86/xen/smp.c
>> +++ b/arch/x86/xen/smp.c
>> @@ -576,24 +576,22 @@ void xen_send_IPI_mask_allbutself(const struct cpumask 
>> *mask,
>>  {
>>         unsigned cpu;
>>         unsigned int this_cpu = smp_processor_id();
>> +       int xen_vector = xen_map_vector(vector);
>>
>> -       if (!(num_online_cpus() > 1))
>> +       if (!(num_online_cpus() > 1) || (xen_vector < 0))
>>                 return;
>>
>>         for_each_cpu_and(cpu, mask, cpu_online_mask) {
>>                 if (this_cpu == cpu)
>>                         continue;
>>
>> -               xen_smp_send_call_function_single_ipi(cpu);
>> +               xen_send_IPI_one(cpu, xen_vector);
>>         }
>>  }
>>
>>  void xen_send_IPI_allbutself(int vector)
>>  {
>> -       int xen_vector = xen_map_vector(vector);
>> -
>> -       if (xen_vector >= 0)
>> -               xen_send_IPI_mask_allbutself(cpu_online_mask, xen_vector);
>> +       xen_send_IPI_mask_allbutself(cpu_online_mask, vector);
>>  }
>>
>>  static irqreturn_t xen_call_function_interrupt(int irq, void *dev_id)
>> diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h
>> index 8981a76..c7c2d89 100644
>> --- a/arch/x86/xen/smp.h
>> +++ b/arch/x86/xen/smp.h
>> @@ -5,7 +5,6 @@ extern void xen_send_IPI_mask(const struct cpumask *mask,
>>  extern void xen_send_IPI_mask_allbutself(const struct cpumask *mask,
>>                                 int vector);
>>  extern void xen_send_IPI_allbutself(int vector);
>> -extern void physflat_send_IPI_allbutself(int vector);
>>  extern void xen_send_IPI_all(int vector);
>>  extern void xen_send_IPI_self(int vector);
>>
>> -- 
>> 1.7.9.5
>>
> 
>

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