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SubjectRe: clocksource changes in 2.6.31 - possible regression
On Mon, 17 Aug 2009, Stephen Hemminger wrote:
> The following commit causes a change for kernels built with HRT but
> not actually using HRT. I typically use the generic kernel we ship
> on test machines, and that kernel has NOHZ and HRT (for power savings/virt
> and HRT for QoS), but I want to be able to enable TSC as a clock source
> when doing performance tests with pktgen.
>
> The machine in question is a several year old Opteron box, that
> normally reports clocksources: acpi_pm jiffies tsc
> but now with 2.6.31-rc6, it only has acpi_pm.
>
> Since HRT/NOHZ is not really runtime configurable, I think the
> proper behavior is:

Isn't highres=off resp. nohz=off on the kernel command line not good
enough ?

> * kernel reports all possible clocksources and chooses the best
> by default
> * if user demands a different clocksource, the kernel should use that
> but degrade if necessary: ie. high-res timers have less (maybe even
> only HZ accuracy), and nohz should be automatically disabled if
> needed

We never implemented to back out from highres/nohz and I have no urge
to do so :)

Thanks,

tglx


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