Re: smp.c && barriers (Was: [PATCH 1/4] generic-smp: remove single ipi fallback for smp_call_function_many())

Ingo Molnar
2009-02-20T19:41:40Z

* Suresh Siddha <suresh.b.siddha@intel.com> wrote:

> > So the question is, is an SFENCE there enough to serialize
> > the WRMSR with previous memory-writes? It's not specified in
> > the x2apic docs as far as i could see.
>
> No. sfence is not enough (wrmsr to x2apic regs was still
> passing ahead). We have done a small experiment to demonstrate
> the issue and adding mfence fixes the issue but not sfence. We
> need a serializing instruction or mfence. I will try to get
> the SDM updated.

Fair enough!

Ingo