Messages in this thread | | | Date | Mon, 17 Aug 2009 09:03:19 -0700 | From | Stephen Hemminger <> | Subject | clocksource changes in 2.6.31 - possible regression |
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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:
* 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
commit 3f68535adad8dd89499505a65fb25d0e02d118cc Author: john stultz <johnstul@us.ibm.com> Date: Wed Jan 21 22:53:22 2009 -0700
clocksource: sanity check sysfs clocksource changes
Thomas, Andrew and Ingo pointed out that we don't have any safety checks in the clocksource sysfs entries to make sure sysadmins don't try to change the clocksource to a non high-res timer capable clocksource (such as jiffies) when high-res timers (HRT) is enabled. Doing so will likely hang a system.
Correct this by filtering non HRT clocksources from available_clocksources and not accepting non HRT clocksources with HRT enabled.
Signed-off-by: John Stultz <johnstul@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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