Messages in this thread | | | Date | Thu, 6 Jul 2006 15:25:43 -0700 | From | Stephane Eranian <> | Subject | Re: cpuinfo_x86 and apicid |
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Suresh,
On Thu, Jul 06, 2006 at 02:06:13PM -0700, Siddha, Suresh B wrote: > 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. > Ah, yes I missed that. It works there two. I had something wrong about how I accessed cpu_data. I am used to the elegant way we do it on IA-64 but on x86_64 you have to index the cpu_data[] array with smp_processor_id(). I was pointing to cpu_data[0] on all processors.
For what I need, I can do cpuinfo_x86->apicid & 0x3 to identify which thread is running. I can now remove some more code in perfmon2.
Thanks for your help.
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