Re: Question about apic ipi interface

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

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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@canonical.com>
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@canonical.com>
---
 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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