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[61.220.137.37]) by smtp.gmail.com with ESMTPSA id i15sm18521965pfr.8.2019.04.10.01.11.54 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Apr 2019 01:11:57 -0700 (PDT) To: Thomas Gleixner Cc: Ingo Molnar , Borislav Petkov , x86@kernel.org, Pavel Tatashin , Peter Zijlstra , "Rafael J. Wysocki" , Dou Liyang , Daniel Vacek , Mike Travis , Xiaoming Gao , You-Sheng Yang , "H. Peter Anvin" , Chuanhua Lei , Juergen Gross , linux-kernel@vger.kernel.org References: <20190408104012.26791-1-vicamo@gmail.com> From: You-Sheng Yang Openpgp: preference=signencrypt Autocrypt: addr=vicamo@gmail.com; keydata= mQINBFxnlfIBEAC2RZLjA5pfvBm/uOPB++2AC5Z+hie/zQnaiwoS+4p1pVeZ80lTPdS57b89 H0k3mD6cwF7lLPmUeL6Gi4vriRsiZNiU9ZWS3AVol1YsAQhidJ5aSGOLn1Vhari9NQYwPYjM +MzbzBtjdaUolvBAGqmWFNUtJ2+C43CSKUykDFxHz5NeYE78z3g/2R4MdIvlTO0vQRQM0eNf prpdriEUjHBbMGZFkHNA0cO9WqyT/hztlwEZkP+nGje+oBeNKNlxCy1zXtQPBrFwlisWLycj DF4St3YzMm6Yv7l4Jz+dO7EUkJcKTlhA6QimF4o0u61ebZ9szemrMHkcK+inRwNVlfILZvIO LOUUks7ExzvtxD66mIrjgqcGcKAU9plc7lSqUWvfKHgiWwU/56Sb8y4BprsWKiGEUWytUGu1 SZclJIibcyG0Ookxx43y00YvCCJAy7svkfJJMu7W6+9vpaTAdvUz5GOr9qncxrHXNR2JD9uy f0S7DXVKDBDhgmrNt2bg1FeP/Y9Nz2U/9SMeV6zNwZBwHos5AxAlY3x0IAAk+GZ6gpjdUXY2 GTb1Y1l9RUp/untzo76ytRs6m8BAdwRjWdBAgQ7xMZFpWTD2Unhi45QAXtHd+WgSi0Nwin/W yzVOoWffgS0Z8+xgOBVOs4HKsb1rr0CwcfJa+bsD4JwxRnAkFwARAQABtCFZb3UtU2hlbmcg 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en-GB Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/4/8 8:03 PM, Thomas Gleixner wrote: > On Mon, 8 Apr 2019, You-Sheng Yang wrote: > >> From: You-Sheng Yang >> >> On Intel CoffeeLake it's observed tsc is always marked unstable >> unexpectedly after entering idle state Package C10(PC10), and then clock >> source is switched to hpet. This patch marks tsc as reliable when CPUID >> matches CoffeeLake. > > This lacks a proper analysis: > > 1) Why is it marked unstable Usually the differences between wd_nsec and cs_nsec in function clocksource_watchdog in kernel/time/clocksource.c would be less than a few thousand nanoseconds. However, when CPU is entering deeper idle state, PC10, the hpet clocksource readings starts to give inaccurate values for unknown reason, and the differences to cs_nsec varies from a few hundred nanoseconds to several hundred millisecond, which is larger than WATCHDOG_THRESHOLD (62.5ms) and finally results in tsc being marked unreliable. No HPET overflow is found when this occurs. > 2) Why is it correct to set that for coffeelake So far this strange behaviour is only found on coffeelake. Besides this, no much I can tell actually. This could be probably wrong, but may serve as a start to bring up some more discussion/investigation to solve the problem. I would be more than willing to help verifying further appropriate fixes. Thank you. You-Sheng Yang