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

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Message-ID: <20140328024348.GA31111@feng-snb>
Date:	Fri, 28 Mar 2014 10:43:48 +0800
From:	Feng Tang <feng.tang@...el.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Clemens Ladisch <clemens@...isch.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <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 02:27:26PM -0700, John Stultz wrote:
> On Thu, Mar 27, 2014 at 12:52 PM, Andy Lutomirski <luto@...capital.net> wrote:
> > On 03/27/2014 04:02 AM, Clemens Ladisch wrote:
> >> Feng Tang wrote:
> >> 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.
> 
> While I suspect the comment above is in relation to the non-apic
> timer. But with respect to timekeeping, our point is true assuming the
> TSC isn't mucked up by the BIOS.  My 1yr old i7-3930k single socket
> system still has some wonky BIOS bug that offsets the boot core's TSC.
> And that's intel's bios, so I can only imagine other vendors have
> found other ways to cause trouble.
> 
> So yea, the hpet availability for timekeeping is still important, as
> the TSC can still be problematic.

Yes, agreed. My patch only provides a way to disable HPET for some specific
platforms :)

Thanks,
Feng
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