Re: [PATCH] acpi_pm: Reduce PMTMR counter read contention

[Thomas Gleixner]

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