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

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Message-ID: <20080227223740.GZ29269@cs181133002.pp.htv.fi>
Date:	Thu, 28 Feb 2008 00:37:40 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	Hiroshi Shimamoto <h-shimamoto@...jp.nec.com>
Cc:	"H. Peter Anvin" <hpa@...or.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 02:16:56PM -0800, Hiroshi Shimamoto wrote:
> Adrian Bunk wrote:
> > 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.
> 
> OK, you say "Don't mix two different semantics into one variable X86_HT", right?

Exactly.

This mixing is not your fault since it's an older problem, but instead 
of your suggested patch we should fix it properly.

> Thanks,
> Hiroshi Shimamoto

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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