From: Prarit Bhargava <prarit@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org,
Patrick Geary <patrickg@supermicro.com>,
Jonathan Corbet <corbet@lwn.net>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org,
Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Juergen Gross <jgross@suse.com>,
"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
Viresh Kumar <viresh.kumar@linaro.org>,
Daniel Drake <drake@endlessm.com>,
Michael Zhivich <mzhivich@akamai.com>,
linux-doc@vger.kernel.org
Subject: Re: [PATCH] x86/tsc: Add kernel options to disable CPUID and MSR calibrations
Date: Thu, 27 Feb 2020 07:58:43 -0500 [thread overview]
Message-ID: <64e49d3f-ac4c-84ca-e663-92f87aae1362@redhat.com> (raw)
In-Reply-To: <87k149nd4p.fsf@nanos.tec.linutronix.de>
On 2/26/20 6:27 PM, Thomas Gleixner wrote:
> Peter Zijlstra <peterz@infradead.org> writes:
>> On Wed, Feb 26, 2020 at 11:43:08AM -0500, Prarit Bhargava wrote:
>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>> index dbc22d684627..0316aadfff08 100644
>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>> @@ -4942,7 +4942,7 @@
>>> See Documentation/admin-guide/mm/transhuge.rst
>>> for more details.
>>>
>>> - tsc= Disable clocksource stability checks for TSC.
>>> + tsc=option[,option...] Various TSC options.
>>> Format: <string>
>>> [x86] reliable: mark tsc clocksource as reliable, this
>>> disables clocksource verification at runtime, as well
>>> @@ -4960,6 +4960,12 @@
>>> in situations with strict latency requirements (where
>>> interruptions from clocksource watchdog are not
>>> acceptable).
>>> + [x86] no_cpuid_calibration: Disable the CPUID TSC
>>> + calibration. Used in situations where the CPUID
>>> + TSC khz does not match the actual CPU TSC khz
>>> + [x86] no_msr_calibration: Disable the MSR TSC
>>> + calibration. Used in situations where the MSR
>>> + TSC khz does not match the actual CPU TSC khz.
>>
>> Do we want to mention that these situations are mostly broken firmware?
>> Also do mention that if you disable these you might not boot due to not
>> having a PIT/HPET at all?
>
> Right. Same discussion as before.
>
> Also why do we want no_cpuid_calibration and no_msr_calibration? How
> should Joe User figure out which one to use? This does not make
> sense. The point is that the BIOS/Firmware supplied value in system
> registers is bogus. So something like "skip_firmware_calibration" might
> be better suitable.
no_cpuid_calibration was required for Patrick's case where the CPU was
overclocked and therefore the CPUID khz value was invalid, but the MSR value is
good. I had to skip both to get to the PIT calibration because I had broken FW.
I don't see how a single skip_firmware_calibration covers these cases.
>
> Aside of that this really wants to be combined with the ability to
> supply the actual frequency on the command line as I suggested in the
> other thread to cope with machines which do not expose PIT/HPET or have
> broken variants of them.
tglx, can you give a lore link to the thread?
Thanks,
P.
>
> Thanks,
>
> tglx
>
>
prev parent reply other threads:[~2020-02-27 12:58 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 16:43 [PATCH] x86/tsc: Add kernel options to disable CPUID and MSR calibrations Prarit Bhargava
2020-02-26 16:54 ` Peter Zijlstra
2020-02-26 23:27 ` Thomas Gleixner
2020-02-27 12:58 ` Prarit Bhargava [this message]
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