lkml.org 
[lkml]   [2015]   [Feb]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: smp_call_function_single lockups
From
On Thu, Feb 19, 2015 at 8:32 AM, Rafael David Tinoco <inaddy@ubuntu.com> wrote:
> Feb 19 08:21:28 derain kernel: [ 3.637682] Switched APIC routing to
> cluster x2apic.

Ok. That "cluster x2apic" mode is just about the nastiest mode when it
comes to sending a single ipi. We do that insane dance where we

- turn single cpu number into cpumask
- copy the cpumask to a percpu temporary storage
- walk each cpu in the cpumask
- for each cpu, look up the cluster siblings
- for each cluster sibling that is also in the cpumask, look up the
logical apic mask and add it to the actual ipi destination mask
- send an ipi to that final mask.

which is just insane. It's complicated, it's fragile, and it's unnecessary.

If we had a simple "send_IPI()" function, we could do this all with
something much saner, and it would look sopmething like

static void x2apic_send_IPI(int cpu, int vector)
{
u32 dest = per_cpu(x86_cpu_to_logical_apicid, cpu);
x2apic_wrmsr_fence();
__x2apic_send_IPI_dest(dest, vector, APIC_DEST_LOGICAL);
}

and then 'void native_send_call_func_single_ipi()' would just look like

void native_send_call_func_single_ipi(int cpu)
{
apic->send_IPI(cpu, CALL_FUNCTION_SINGLE_VECTOR);
}

but I might have missed something (and we might want to have a wrapper
that says "if the apic doesn't have a 'send_IPI' function, use
"send_IPI_mask(cpumask_of(cpu, vector) instead"

The fact that you need that no_x2apic_optout (which in turn means that
your ACPI tables seem to say "don't use x2apic") also makes me worry.

Are there known errata for the x2apic?

Linus


\
 
 \ /
  Last update: 2015-02-19 18:21    [W:0.496 / U:0.056 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site