linux-kernel - Re: [PATCH] x86: X86_HT always enable on X86

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Message-ID: <20080227215816.GX29269@cs181133002.pp.htv.fi>
Date:	Wed, 27 Feb 2008 23:58:16 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sam Ravnborg <sam@...nborg.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: X86_HT always enable on X86_64 SMP

On Wed, Feb 27, 2008 at 01:30:59PM -0800, H. Peter Anvin wrote:
> Adrian Bunk wrote:
>> On Wed, Feb 27, 2008 at 01:16:30PM -0800, Hiroshi Shimamoto wrote:
>>> From: Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
>>>
>>> X86_HT is used for hyperthreading or multicore on 32-bit.
>>> The X86_HT on 64-bit is different from 32-bit, it means hyperthreading only.
>>> And X86_HT is not used on 64-bit except from cpu/initel_cacheinfo.c.
>>>
>>> Unify X86_HT for hyperthreading or multicore.
>>> Turn X86_HT on when X86_64 and SMP are enabled.
>>
>> Please fix it properly instead - fiddling around with it the way you do
>> only asks for trouble in the future.
>>
>> What we need are two different variables for:
>> - hyperthreading and
>> - multicore
>
> He does, and calls them SCHED_SMT and SCHED_MC respectively.

These are the already existing scheduler related variables that are 
only a part of the X86_HT usages.

> It's not particularly clear to me what X86_HT is meant to be used for  
> anymore at all.

grep through the source code and you find it is sometimes used for 
hyperthreading and sometimes for multicore.

I don't care whether X86_HT gets splitted or perhaps even removed, but 
any change to it should remove the status quo of it having two different 
semantics.

> 	-hpa

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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