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

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Date:	Tue, 4 Jan 2011 16:35:00 +0100
From:	Stephane Eranian <eranian@...gle.com>
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>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] perf: Check if HT is supported and enabled

On Tue, Jan 4, 2011 at 2:58 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> On Tue, 2011-01-04 at 14:52 +0100, Stephane Eranian wrote:
>>
>> Couldn't you simply over-provision, and then when the CPU is online, use my
>> ht_enabled statement to figure out whether or not you need to handle the sharing
>> issue?
>
> That's pretty much what Lin's latest does:
>
>  X86_FEATURE_HT && smp_num_siblings > 1
>
> shows the CPU is capable of HT and will allocate the needed resources.
>
Ok, but once the CPU is online, you can still check whether or not HT is
enabled. If not, then you don't need to bother with the MSR sharing code.
So you may allocate a data structure which you won't use and I think that's
fine given we don't have a good way of figuring out whether HT is enabled
or not.
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