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

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Message-ID: <CANcMJZD7PNf-toZ3FyT-NEUs=YnW5ZZ54cCOkziKDb-wZrOoyA@mail.gmail.com>
Date:	Thu, 27 Mar 2014 14:27:26 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Clemens Ladisch <clemens@...isch.de>,
	Feng Tang <feng.tang@...el.com>,
	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 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.

thanks
-john
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