Messages in this thread | | | Date | Wed, 15 May 2013 09:53:25 -0700 | From | John Stultz <> | Subject | Re: [patch 07/15] clocksource: Provide unbind interface in sysfs |
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On 05/15/2013 02:47 AM, Thomas Gleixner wrote: > On Mon, 29 Apr 2013, John Stultz wrote: >> On 04/25/2013 01:31 PM, Thomas Gleixner wrote: >>> With the module refcount held for the current clocksource there is no >>> way to unload the module. >>> >>> Provide a sysfs interface which allows to unbind the clocksource. One >>> could argue that the clocksource override could be (ab)used to do so, >>> but the clocksource override cannot be used from the kernel itself, >>> while an unbind function can be used to programmatically check whether >>> a clocksource can be shutdown or not. >>> >>> The unbind functionality uses the new skip current feature of >>> clocksource_select and verifies that a fallback clocksource has been >>> installed. If the clocksource which should be unbound is the current >>> clocksource and no fallback can be found, unbind returns -EBUSY. >>> >>> This does not support the unbinding of a clocksource which is used as >>> the watchdog clocksource. No point in fostering crappy hardware. >> So.. if the clocksource you want to unbind is the highest rated continuous >> clocksource that doesn't need a watchdog (basically what's likely to be in-use >> and required to be unbinded), its likely to be selected as the watchdog >> already. >> >> ie: on a system that has only HPET/ACPI_PM, you can't unbind HPET, since its a >> watchdog. > No. The thing is that I only prevent unbinding if it is used as the > watchdog. In the above HPET/PM scenario both are potential watchdogs, > but w/o a user it's valid to unbind one of them. > > What I need to prevent is: > > TSC is current clocksource and we only have ACPI_PM as watchdog and > its used. So now you try to unbind ACPI_PM then the TSC would be left > w/o a watchdog instance. That's what I'm preventing. Will reword the > changelog accordingly.
You might double check the logic, because I feel like I actually hit this issue where on my vm machine w/ only hpet/acpi_pm I couldn't unbind the hpet.
Though its been a few weeks, so maybe I'm confusing things? Let me know if you want me to try to reproduce it.
thanks -john
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