linux-kernel - Re: [PATCH] x86: hpet: Don't default CONFIG_HPET_TIMER to be y for X86

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Message-ID: <20140328024813.GB31111@feng-snb>
Date:	Fri, 28 Mar 2014 10:48:13 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Clemens Ladisch <clemens@...isch.de>, tglx@...utronix.de,
	mingo@...e.hu, hpa@...or.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: hpet: Don't default CONFIG_HPET_TIMER to be y for
 X86_64

On Thu, Mar 27, 2014 at 12:52:57PM -0700, Andy Lutomirski wrote:
> On 03/27/2014 04:02 AM, Clemens Ladisch wrote:
> > Feng Tang wrote:
> >> On many new phone/tablet platforms like Baytrail/Merrifield etc,
> >> the HPET are either defeatured or has some problem to be used
> >> as a reliable timer. As these platforms also have X86_64, we
> >> should not make HPET_TIMER default y for all X86_64.
> 
> Wouldn't it be better to fix the hpet driver so that the hpet doesn't
> used on these platforms?
> 
> > 
> > The help text still says:
> > | You can safely choose Y here.  [...]
> > | Choose N to continue using the legacy 8254 timer.
> > 
> > Are these statements still true for those platforms?
> 
> They aren't true for modern desktop and server platforms -- the TSC is
> used regardless of hpet availability.

The way of using TSC varies depends on the generations of platforms.
Thomas Gleixner once gave a very good description, which link I personally
bookmarked, and would share here:
	https://lkml.org/lkml/2013/5/8/202

Thanks,
Feng

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