Re: [PATCH] x86/intel: Disable HPET on another Intel Coffee Lake platform

From: Jakub Kicinski <kuba@kernel.org>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: x86@kernel.org, jose.souza@intel.com, hpa@zytor.com,
	bp@alien8.de, mingo@redhat.com, tglx@linutronix.de,
	kai.heng.feng@canonical.com, bhelgaas@google.com,
	linux-pci@vger.kernel.org, rudolph@fb.com, xapienz@fb.com,
	bmilton@fb.com, stable@vger.kernel.org, paulmck@kernel.org
Subject: Re: [PATCH] x86/intel: Disable HPET on another Intel Coffee Lake platform
Date: Thu, 16 Sep 2021 08:30:42 -0700	[thread overview]
Message-ID: <20210916083042.5f63163a@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <20210916150707.GA1611532@bjorn-Precision-5520>

On Thu, 16 Sep 2021 10:07:07 -0500 Bjorn Helgaas wrote:
> On Thu, Sep 16, 2021 at 06:17:39AM -0700, Jakub Kicinski wrote:
> > My Lenovo T490s with i7-8665U had been marking TSC as unstable
> > since v5.13, resulting in very sluggish desktop experience...  
> 
> Including the actual dmesg log line here might help others locate this
> fix.

Good point, will add in v2.

clocksource: timekeeping watchdog on CPU3: hpet read-back delay of 316000ns, attempt 4, marking unstable
tsc: Marking TSC unstable due to clocksource watchdog
TSC found unstable after boot, most likely due to broken BIOS. Use 'tsc=unstable'.
sched_clock: Marking unstable (14539801827657, -530891666)<-(14539319241737, -48307500)
clocksource: Checking clocksource tsc synchronization from CPU 3 to CPUs 0-2,6-7.
clocksource: Switched to clocksource hpet

> > I have a 8086:3e34 bridge, also known as "Host bridge: Intel
> > Corporation Coffee Lake HOST and DRAM Controller (rev 0c)".
> > Add it to the list.
> > 
> > We should perhaps consider applying this quirk more widely.
> > The Intel documentation does not list my device [1], but
> > linuxhw [2] does, and it seems to list a few more bridges
> > we do not currently cover (3e31, 3ecc, 3e35, 3e0f).  
> 
> In the fine tradition of:
> 
>   e0748539e3d5 ("x86/intel: Disable HPET on Intel Ice Lake platforms")
>   f8edbde885bb ("x86/intel: Disable HPET on Intel Coffee Lake H platforms")
>   fc5db58539b4 ("x86/quirks: Disable HPET on Intel Coffe Lake platforms")
>   62187910b0fc ("x86/intel: Add quirk to disable HPET for the Baytrail plat form")
> 
> This seems to be an ongoing issue, not just a point defect in a single
> product, and I really hate the onesy-twosy nature of this.

Indeed. Or at least cover all Coffee Lakes in one fell swoop.

> Is there really no way to detect this issue automatically or fix
> whatever Linux bug makes us trip over this?  I am no clock expert, so
> I have absolutely no idea whether this is possible.

I'm deferring to clock experts. Paul mentioned he has some prototype
patches that may help.

> > [1] https://www.intel.com/content/dam/www/public/us/en/documents/datasheets/8th-gen-core-family-datasheet-vol-2.pdf
> > [2] https://github.com/linuxhw/DevicePopulation/blob/master/README.md
> > 
> > Cc: stable@vger.kernel.org # v5.13+  
> 
> How did you pick v5.13?  force_disable_hpet() was added by
> 62187910b0fc ("x86/intel: Add quirk to disable HPET for the Baytrail
> platform"), which appeared in v3.15.

Erm, good question, it started happening for me (and others with the
same laptop) with v5.13. I just sort of assumed it was 2e27e793e280
("clocksource: Reduce clocksource-skew threshold"). 

It usually takes  a day to repro (4 hours was the quickest repro I've
seen) so bisection was kind of out of question.