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To:     Thomas Gleixner <tglx@linutronix.de>,
        You-Sheng Yang <vicamo@gmail.com>
Cc:     Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org, Pavel Tatashin <pasha.tatashin@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Dou Liyang <douly.fnst@cn.fujitsu.com>,
        Daniel Vacek <neelx@redhat.com>,
        Mike Travis <mike.travis@hpe.com>,
        Xiaoming Gao <gxm.linux.kernel@gmail.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Chuanhua Lei <chuanhua.lei@linux.intel.com>,
        Juergen Gross <jgross@suse.com>, linux-kernel@vger.kernel.org
References: <20190408104012.26791-1-vicamo@gmail.com>
 <alpine.DEB.2.21.1904081403220.1748@nanos.tec.linutronix.de>
From:   You-Sheng Yang <vicamo.yang@canonical.com>
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Subject: Re: [PATCH] x86/tsc: mark tsc reliable on CoffeeLake
Message-ID: <bc576802-9029-3e52-f831-ba955b222898@canonical.com>
Date:   Fri, 12 Apr 2019 11:28:12 +0800
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In-Reply-To: <alpine.DEB.2.21.1904081403220.1748@nanos.tec.linutronix.de>
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From: You-Sheng Yang <vicamo.yang@canonical.com>
To: Thomas Gleixner <tglx@linutronix.de>, You-Sheng Yang <vicamo@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
 x86@kernel.org, Pavel Tatashin <pasha.tatashin@oracle.com>,
 Peter Zijlstra <peterz@infradead.org>,
 "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
 Dou Liyang <douly.fnst@cn.fujitsu.com>, Daniel Vacek <neelx@redhat.com>,
 Mike Travis <mike.travis@hpe.com>, Xiaoming Gao
 <gxm.linux.kernel@gmail.com>, "H. Peter Anvin" <hpa@zytor.com>,
 Chuanhua Lei <chuanhua.lei@linux.intel.com>, Juergen Gross
 <jgross@suse.com>, linux-kernel@vger.kernel.org
Message-ID: <bc576802-9029-3e52-f831-ba955b222898@canonical.com>
Subject: Re: [PATCH] x86/tsc: mark tsc reliable on CoffeeLake
References: <20190408104012.26791-1-vicamo@gmail.com>
 <alpine.DEB.2.21.1904081403220.1748@nanos.tec.linutronix.de>
In-Reply-To: <alpine.DEB.2.21.1904081403220.1748@nanos.tec.linutronix.de>

--dSuZ5aXFliqye4GciFuQdyADaU5yJPNCA
Content-Type: text/plain; charset=utf-8
Content-Language: en-GB
Content-Transfer-Encoding: quoted-printable

On 2019/4/8 8:03 PM, Thomas Gleixner wrote:
> On Mon, 8 Apr 2019, You-Sheng Yang wrote:
>> +	/*
>> +	 * On Intel CoffeeLake, tsc may be marked unstable unexpectedly afte=
r
>> +	 * entering PC10.
>> +	 */
>> +	if (boot_cpu_data.x86_vendor =3D=3D X86_VENDOR_INTEL &&
>> +	    (boot_cpu_data.x86_model =3D=3D INTEL_FAM6_KABYLAKE_MOBILE ||
>> +	     boot_cpu_data.x86_model =3D=3D INTEL_FAM6_KABYLAKE_DESKTOP) &&
>> +	    boot_cpu_data.x86_stepping >=3D 0x0a)
>> +		tsc_clocksource_reliable =3D 1;
>=20
> No. We are not starting that family/model/stepping game especially not
> with random stepping cutoffs which are pulled out of thin air.  That's
> going to spiral out of control sooner than later.

What about we simply disable clocksource watchdog if this is an
invariant TSC?

> There must be a better way to do that. Rafael?
>=20
> Thanks,
>=20
> 	tglx

You-Sheng Yang


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