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From: Stephane Eranian <eranian@hpl.hp.com>
To: linux-kernel@vger.kernel.org
Cc: perfmon@napali.hpl.hp.com, Stephane Eranian <eranian@hpl.hp.com>
Subject: cpuinfo_x86 and apicid
Date: Thu, 6 Jul 2006 08:01:18 -0700	[thread overview]
Message-ID: <20060706150118.GB10110@frankl.hpl.hp.com> (raw)

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?

Thanks.

-- 
-Stephane

             reply	other threads:[~2006-07-06 15:09 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-07-06 15:01 Stephane Eranian [this message]
2006-07-06 15:27 ` linux-os (Dick Johnson)
2006-07-06 16:19 ` Siddha, Suresh B
2006-07-06 20:00   ` Stephane Eranian
2006-07-06 21:06     ` Siddha, Suresh B
2006-07-06 22:25       ` Stephane Eranian
2006-07-06 22:37         ` [perfmon] " Stephane Eranian
2006-07-06 22:47           ` Siddha, Suresh B

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