Messages in this thread | | | Date | Thu, 2 Oct 2008 10:07:26 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH,RFC] RCU-based detection of stalled CPUs for Classic RCU |
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* Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
> Hello! > > This patch adds stalled-CPU detection to Classic RCU. This capability > is enabled by a new config variable CONFIG_RCU_CPU_STALL_DETECTOR, > which defaults disabled. This is a debugging feature, not something > that non-kernel-hackers would be expected to care about. This feature > can detect looping CPUs in !PREEMPT builds and looping CPUs with > preemption disabled in PREEMPT builds. This is essentially a port of > this functionality from the treercu patch. > > One current shortcoming: on some systems, stalls are detected during > early boot, when we normally would not care about them. My thought is > to add a call from late initialization to suppress stall detection > until the system is well along its way to being booted, but thought I > should check to see if there might already be something for this > purpose.
could you be a bit more specific, why do those warnings show up and why dont we care about them? There are things like networking that occasionally do an rcu_sync() and a stall could mean a bootup hang.
> (Currently against 2.6.27-rc8, FYI.) > > Thoughts? > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
i think this is a very good idea in general - often the question comes up whether a hang seen in the RCU code is indeed caused by RCU or other factors. Could you perhaps rebase it against tip/core/rcu ? [or tip/master for convenience]
Ingo
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