Messages in this thread Patch in this message | | | Date | Tue, 12 Aug 2008 17:25:03 -0700 | From | "Paul E. McKenney" <> | Subject | [PATCH diagnostic] Prevent console flood when one CPU sees another AWOL via RCU |
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On Mon, Aug 11, 2008 at 06:17:28AM -0700, Paul E. McKenney wrote: > On Mon, Aug 11, 2008 at 01:38:17PM +0200, Ingo Molnar wrote: > > > > * Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > > > > And here is the patch. It is still a bit raw, so the results should > > > be viewed with some suspicion. It adds a default-off kernel parameter > > > CONFIG_RCU_CPU_STALL which must be enabled. > > > > > > Rather than exponential backoff, it backs off to once per 30 seconds. > > > My feeling upon thinking on it was that if you have stalled RCU grace > > > periods for that long, a few extra printk() messages are probably the > > > least of your worries... > > > > while this wont debug problems were timer irqs are genuinely stuck for > > long periods of time, it should find problems with RCU completion logic > > itself in the presence of correct timer irqs - and the lack of any > > messages from this debug option should point the finger more firmly in > > the direction of stalled timer irqs. > > > > So i find this debug feature rather useful and have applied it to > > tip/core/rcu (and cleaned it up a bit). I renamed the config option to > > CONFIG_DEBUG_RCU_STALL to make it more in line with usual debug option > > names. Lets see whether -tip testing finds any false positives. > > Sounds good! > > For whatever it is worth, this diagnostic can also locate latency issues > in non-CONFIG_PREEMPT kernels, even when those problems are outside of > preempt_disable() regions. Latency tracer is of course a better tool > for things -inside- of preempt_disable() regions.
One small change needed to keep from flooding the console when one CPU notices that another is AWOL. Unless I am missing something subtle. Otherwise the cleanups look good!
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> ---
rcuclassic.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/kernel/rcuclassic.c b/kernel/rcuclassic.c index 56b8712..dab2676 100644 --- a/kernel/rcuclassic.c +++ b/kernel/rcuclassic.c @@ -308,6 +308,7 @@ static void print_other_cpu_stall(struct rcu_ctrlblk *rcp) spin_unlock(&rcp->lock); return; } + rcp->gp_check = get_seconds() + 30; spin_unlock(&rcp->lock); /* OK, time to rat on our buddy... */
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