Subject: Re: linux-next: manual merge of the tip tree with the sparc tree

From: Peter Zijlstra <[email-masked]>
Date: Fri, 20 May 2011 10:11:53 +0200

On Fri, 2011-05-20 at 08:07 +0200, Daniel Hellstrom wrote:
> Peter Zijlstra wrote:
> 
> >On Thu, 2011-05-19 at 15:37 +0200, Daniel Hellstrom wrote:
> >
> >
> >  
> >
> >>diff --git a/arch/sparc/kernel/smp_32.c b/arch/sparc/kernel/smp_32.c
> >>index 41102c5..d5b3958 100644
> >>--- a/arch/sparc/kernel/smp_32.c
> >>+++ b/arch/sparc/kernel/smp_32.c
> >>@@ -156,11 +156,11 @@ void arch_send_call_function_ipi_mask(const struct 
> >>cpumask *mask)
> >>
> >> void smp_resched_interrupt(void)
> >> {
> >>+       irq_enter();
> >>+       scheduler_ipi();
> >>        local_cpu_data().irq_resched_count++;
> >>-       /*
> >>-        * do nothing, since it all was about calling re-schedule
> >>-        * routine called by interrupt return code.
> >>-        */
> >>+       irq_exit();
> >>+       /* re-schedule routine called by interrupt return code. */
> >> }
> >>    
> >>
> >
> >That doesn't look like an IPI, that looks like its calls the function on
> >the local cpu, which is completely pointless.
> >  
> >
> The above function is one of the IPI interrupt handlers.
> 
> The smp_send_reschedule() is called by the generic code, it is 
> responsible for sending an IRQ to the target CPU, that CPU comes into 
> smp_resched_interrupt above from the IRQ trap handler. So yes, the 
> scheduler_ipi() is called on the local CPU, but on the CPU taking the 
> IPI not the CPU sending the IPI.

Ah, clearly I cannot read well, I actually thought that was
smp_send_reschedule(). OK, if sparc32 is now actually sending IPIs and
the above is the handler, then you're completely right, sorry for the
confusion.

Also, since sparc32 now grew this IPI, you can remove:

+++ b/init/Kconfig
@@ -827,6 +827,11 @@ config SCHED_AUTOGROUP
          desktop applications.  Task group autogeneration is currently based
          upon task session.
 
+config SCHED_TTWU_QUEUE
+       bool
+       depends on !SPARC32
+       default y
+
 config MM_OWNER
        bool