linux-kernel - Re: [PATCH 4/7] perf: Check if HT is supported and enabled

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Date:	Tue, 04 Jan 2011 13:55:27 -0500
From:	Valdis.Kletnieks@...edu
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Lin Ming <ming.m.lin@...el.com>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] perf: Check if HT is supported and enabled

On Tue, 04 Jan 2011 12:10:19 +0100, Peter Zijlstra said:

> X86_FEATURE_HT tells us the CPU supports telling us about HT,
> smp_num_siblings > 1 tells us the CPU is capable of HT.

A subtle but important distinction. Several laptops ago, I had a P4-M chip that
had FEATURE_HT, but num_siblings == 1.  ISTR trying to boot an SMP kernel on it
and it dying gloriously trying to bring up the non-existent other sibling.


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