linux-kernel - Re: [RFD] x86/tsc: Loosen the requirements for watchdog - (was x86/hpet: Disable HPET on Intel Coffe Lake)

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Message-ID: <CAD8Lp46vG2TEAareYnLNLACkLOoNmsvUoFS64e+zgNfq0DH6EA@mail.gmail.com>
Date:   Fri, 30 Aug 2019 11:47:02 +0800
From:   Daniel Drake <drake@...lessm.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, harry.pan@...el.com,
        x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Len Brown <lenb@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>, Pu Wen <puwen@...on.cn>
Subject: Re: [RFD] x86/tsc: Loosen the requirements for watchdog - (was
 x86/hpet: Disable HPET on Intel Coffe Lake)

Hi Thomas,

On Fri, Aug 30, 2019 at 5:38 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> So if we have to disable the HPET on Kaby Lake alltogether unless Intel
> comes up with the clever fix, i.e. poking at the right registers, then I
> think we should also lift the TSC watchdog restrictions on these machines
> if they are single socket, which they are as the affected CPUs so far are
> mobile and client types.
>
> Also given the fact that we get more and more 'reduced' hardware exposed
> via ACPI and we already dealt with quite some fallout with various related
> issues due to that, I fear we need to bite this bullet anyway anytime soon.

Thanks for the explanation here!

My experience in this area is basically limited to the clock-related
issues that I've sent your way recently, so I don't have deep wisdom
to draw upon, but what you wrote here makes sense to me.

If you can outline a testing procedure, we can test upcoming patches
on Coffee Lake and Kaby Lake consumer laptops.

Thanks,
Daniel