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McKenney" Cc: Xing Zhengjun , John Stultz , Stephen Boyd , Jonathan Corbet , Mark Rutland , Marc Zyngier , Andi Kleen , Chris Mason , LKML , lkp@lists.01.org, lkp@intel.com Subject: Re: [LKP] Re: [clocksource] 6c52b5f3cf: stress-ng.opcode.ops_per_sec -14.4% regression In-Reply-To: <20210424122920.GB85095@shbuild999.sh.intel.com> References: <20210420134331.GM975577@paulmck-ThinkPad-P17-Gen-1> <20210420140552.GA3158164@paulmck-ThinkPad-P17-Gen-1> <04f4752e-6c5a-8439-fe75-6363d212c7b2@intel.com> <20210421134224.GR975577@paulmck-ThinkPad-P17-Gen-1> <20210422074126.GA85095@shbuild999.sh.intel.com> <20210422142454.GD975577@paulmck-ThinkPad-P17-Gen-1> <20210422165743.GA162649@paulmck-ThinkPad-P17-Gen-1> <20210423061115.GA62813@shbuild999.sh.intel.com> <20210423140254.GM975577@paulmck-ThinkPad-P17-Gen-1> <20210424122920.GB85095@shbuild999.sh.intel.com> Date: Mon, 26 Apr 2021 14:39:25 +0200 Message-ID: <87pmyhte2q.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Apr 24 2021 at 20:29, Feng Tang wrote: > On Fri, Apr 23, 2021 at 07:02:54AM -0700, Paul E. McKenney wrote: > And I'm eager to know if there is any real case of an unreliable tsc > on the 'large numbers' of x86 system which complies with our cpu feature > check. And if there is, my 2/2 definitely should be dropped. Nothing prevents BIOS tinkerers from trying to be 'smart'. My most recent encounter (3 month ago) was on a laptop where TSC drifted off on CPU0 very slowly, but was caught due to the TSC_ADJUST check in idle. I'm still thinking about a solution to avoid that extra timer and the watchdog for these systems, but haven't found anything which I don't hate with a passion yet. Thanks, tglx