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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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