Re: cpuinfo_x86 and apicid

[Stephane Eranian <eranian@hpl.hp.com>]

On Thu, Jul 06, 2006 at 09:19:30AM -0700, Siddha, Suresh B wrote:
> On Thu, Jul 06, 2006 at 08:01:18AM -0700, Stephane Eranian wrote:
> > Hello,
> > 
> > 
> > In the context of the perfmon2 subsystem for processor with HyperThreading,
> > we need to know on which thread we are currently running. This comes from
> > the fact that the performance counters are shared between the two threads.
> > 
> > We use the thread id (smt_id) because we split the counters in half
> > between the two threads such that two threads on the same core can run
> > with monitoring on.  We are currently computing the smt_id from the
> > apicid as returned by a CPUID instruction. This is not very efficient.
> > 
> > I looked through the i386 code and could not find a function nor 
> > structure that would return this smt_id. In the cpuinfo_x86 structure
> > there is an apicid field that looks good, yet it does not seem to be
> > initialized nor used.
> > 
> > Is cpuinfo_x86->apicid field obsolete? 
> > If so, what is replacing it?
> 
> In i386, it is getting initialized in generic_identify() in common.c and
> it is getting used for example in intel_cacheinfo.c
> 
Well, yes this is exactly what I want, except that it is not compiled for x86_64
so on a HT Xeon in 64-bit I don't get it. Why is that?

-- 

-Stephane