rcu self-detected stall messages on OMAP3, 4 boards
paul at pwsan.com
Sat Sep 22 14:42:08 EDT 2012
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?
> 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
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