Re: cpuinfo_x86 and apicid

[Siddha, Suresh B]

On Thu, Jul 06, 2006 at 01:00:31PM -0700, Stephane Eranian wrote:
> 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?

on x86_64, it is getting initialized in identify_cpu() and further
intel_cacheinfo.c gets linked in both i386 and x86_64.

thanks,
suresh
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