From: Thomas Gleixner <tglx@linutronix.de>
To: Feng Tang <feng.tang@intel.com>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, linux-pci@vger.kernel.org,
linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
Kai-Heng Feng <kai.heng.feng@canonical.com>,
rui.zhang@intel.com, len.brown@intel.com
Subject: Re: [PATCH] x86/PCI: Convert force_disable_hpet() to standard quirk
Date: Mon, 30 Nov 2020 20:21:03 +0100 [thread overview]
Message-ID: <87eekairc0.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20201127061131.GB105524@shbuild999.sh.intel.com>
Feng,
On Fri, Nov 27 2020 at 14:11, Feng Tang wrote:
> On Fri, Nov 27, 2020 at 12:27:34AM +0100, Thomas Gleixner wrote:
>> On Thu, Nov 26 2020 at 09:24, Feng Tang wrote:
>> Yes, that can happen. But OTOH, we should start to think about the
>> requirements for using the TSC watchdog.
>>
>> I'm inclined to lift that requirement when the CPU has:
>>
>> 1) X86_FEATURE_CONSTANT_TSC
>> 2) X86_FEATURE_NONSTOP_TSC
>
>> 3) X86_FEATURE_NONSTOP_TSC_S3
> IIUC, this feature exists for several generations of Atom platforms,
> and it is always coupled with 1) and 2), so it could be skipped for
> the checking.
Yes, we can ignore that bit as it's not widely available and not
required to solve the problem.
>> 4) X86_FEATURE_TSC_ADJUST
>>
>> 5) At max. 4 sockets
>>
>> The only reason I hate to disable HPET upfront at least during boot is
>> that HPET is the best mechanism for the refined TSC calibration. PMTIMER
>> sucks because it's slow and wraps around pretty quick.
>>
>> So we could do the following even on platforms where HPET stops in some
>> magic PC? state:
>>
>> - Register it during early boot as clocksource
>>
>> - Prevent the enablement as clockevent and the chardev hpet timer muck
>>
>> - Prevent the magic PC? state up to the point where the refined
>> TSC calibration is finished.
>>
>> - Unregister it once the TSC has taken over as system clocksource and
>> enable the magic PC? state in which HPET gets disfunctional.
>
> This looks reasonable to me.
>
> I have thought about lowering the hpet rating to lower than PMTIMER, so it
> still contributes in early boot phase, and fades out after PMTIMER is
> initialised.
Not a good idea. pm_timer is initialized before the refined calibration
finishes.
Thanks,
tglx
next prev parent reply other threads:[~2020-11-30 19:22 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-19 18:19 [PATCH] x86/PCI: Convert force_disable_hpet() to standard quirk Bjorn Helgaas
2020-11-24 23:27 ` Bjorn Helgaas
2020-11-25 12:46 ` Thomas Gleixner
2020-11-25 19:13 ` Bjorn Helgaas
2020-11-26 0:50 ` Thomas Gleixner
2020-11-26 1:24 ` Feng Tang
2020-11-26 23:27 ` Thomas Gleixner
2020-11-27 6:11 ` Feng Tang
2020-11-30 19:21 ` Thomas Gleixner [this message]
2020-12-01 8:34 ` Feng Tang
2020-12-02 7:28 ` Zhang Rui
2022-09-29 15:52 ` Yu Liao
2022-09-30 0:38 ` Feng Tang
2022-09-30 1:05 ` Xiongfeng Wang
2022-09-30 1:15 ` Feng Tang
2022-09-30 9:45 ` Yu Liao
2022-09-30 10:13 ` Feng Tang
2022-10-01 5:18 ` Zhang Rui
2022-10-01 12:00 ` Feng Tang
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