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Date:   Wed, 30 Jan 2019 09:06:02 +0100 (CET)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Zhenzhong Duan <zhenzhong.duan@oracle.com>
cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Waiman Long <longman@redhat.com>,
        Srinivas Eeda <srinivas.eeda@oracle.com>
Subject: Re: [PATCH] acpi_pm: Reduce PMTMR counter read contention
In-Reply-To: <1548141807-25825-1-git-send-email-zhenzhong.duan@oracle.com>
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References: <1548141807-25825-1-git-send-email-zhenzhong.duan@oracle.com>
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On Tue, 22 Jan 2019, Zhenzhong Duan wrote:

> On a large system with many CPUs, using PMTMR as the clock source can
> have a significant impact on the overall system performance because
> of the following reasons:
>  1) There is a single PMTMR counter shared by all the CPUs.
>  2) PMTMR counter reading is a very slow operation.
> 
> Using PMTMR as the default clock source may happen when, for example,
> the TSC clock calibration exceeds the allowable tolerance and HPET
> disabled by nohpet on kernel command line. Sometimes the performance

The question is why would anyone disable HPET on a larger machine when the
TSC is wreckaged?

I'm not against the change per se, but I really want to understand why we
need all the complexity for something which should never be used in a real
world deployment.

Thanks,

	tglx