Messages in this thread |  | | | Date | Sat, 22 Sep 2012 18:42:08 +0000 (UTC) | | From | Paul Walmsley <> | | Subject | Re: rcu self-detected stall messages on OMAP3, 4 boards |
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On Fri, 21 Sep 2012, Paul E. McKenney wrote:
> Could you please point me to a recipe for creating a minimal userspace? > Just in case it is the userspac erather than the architecture/hardware > that makes the difference.
Tony's suggestion is pretty good. Note that there may also be differences in kernel timers -- either between x86 and ARM architectures, or loaded device drivers -- that may confound the problem.
> Just to make sure I understand the combinations: > > o All stalls have happened when running a minimal userspace. > o CONFIG_NO_HZ=n suppresses the stalls. > o CONFIG_RCU_FAST_NO_HZ (which depends on CONFIG_NO_HZ=y) has > no observable effect on the stalls. > > Did I get that right, or am I missing a combination?
That's correct.
> Indeed, rcu_idle_gp_timer_func() is a bit strange in that it is > cancelled upon exit from idle, and therefore should (almost) never > actually execute. Its sole purpose is to wake up the CPU. ;-)
Right. Just curious, what would wake up the kernel from idle to handle a grace period expiration when CONFIG_RCU_FAST_NO_HZ=n? On a very idle system, the time between timer ticks could potentially be several tens of seconds.
- Paul
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