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Re: [Xen-devel] [PATCH] x86: avoid HPET use on certain Intel platforms


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Fri, 22 Nov 2019 12:58:45 +0000
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  • Cc: Juergen Gross <jgross@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Delivery-date: Fri, 22 Nov 2019 12:58:55 +0000
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  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 22/11/2019 12:57, Jan Beulich wrote:
> On 22.11.2019 13:50, Andrew Cooper wrote:
>> On 22/11/2019 12:46, Jan Beulich wrote:
>>> Linux commit fc5db58539b49351e76f19817ed1102bf7c712d0 says
>>>
>>> "Some Coffee Lake platforms have a skewed HPET timer once the SoCs entered
>>>  PC10, which in consequence marks TSC as unstable because HPET is used as
>>>  watchdog clocksource for TSC."
>>>
>>> Follow this for Xen as well. Looking at its patch context made me notice
>>> they have a pre-existing quirk for Bay Trail as well. The comment there,
>>> however, points at a Cherry Trail document. Looking at the datasheets of
>>> both, there appear to be similar issues, so go beyond Linux'es coverage
>>> and exclude both. Also key the disable on the PCI IDs of the actual
>>> affected devices, rather than those of 00:00.0.
>>>
>>> Apply the workarounds only when the use of HPET was not explicitly
>>> requested on the command line and when use of (deep) C-states was not
>>> disabled.
>>>
>>> Adjust a few types in touched or nearby code at the same time.
>> Reported-by ?
> The Linux commit has a Suggested-by, but no Reported-by. Do you
> want me to copy that one? Or else do you have any suggestion as
> to who the reporter was?

Well - this patch was identified by someone on xen-devel, which I
presume was your basis for looking into it.

~Andrew

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