RE: [Xen-devel] RE: [PATCH] clocksource=tsc

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

>From: Dan Magenheimer
>Sent: 2008年7月15日 2:00
>
>> I'm sympathetic to the patch, but it looks like an ugly hack 
>> right now.
>
>> Since it should clearly only affect behaviour when the new
>> clocksource is explicitly selected...
>
>Actually the ugliness is because the read_counter function
>and plt_mask are both u32 and I worried that changing them to
>a u64 would be too invasive.
>
>So here's two possible replacement patches, one with those
>switched to u64 and the other with separate 32- and 64-bit
>read_counter functions.  Both are boot-tested with and
>without clocksource=tsc.
>
>Dan

Boot option is good enough for now, but finally I guess you may
need some type of dynamic clocksource switch mechanism,
just like what Linux does today. User may be not sure of the
specific platform. Some features may affect TSC stabilitity, e.g.
Px may have freq change and Cx may have TSC stop on some
platform. On those path a mark_tsc_unstable step is required
to switch current clocksource to other available platfrom timer
on the fly. So besides the boot option, Xen itself needs to code
such condition checks for TSC stability. :-)

Thanks,
Kevin

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