Messages in this thread | | | Date | Thu, 20 Sep 2012 20:04:22 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH rcu] Move TINY_RCU quiescent state out of extended quiescent state |
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On Fri, Sep 21, 2012 at 10:08:56AM +0800, Li Zhong wrote: > TINY_RCU's rcu_idle_enter_common() invokes rcu_sched_qs() in order > to inform the RCU core of the quiescent state implied by idle entry. > Of course, idle is also an extended quiescent state, so that the call > to rcu_sched_qs() speeds up RCU's invoking of any callbacks that might > be queued. This speed-up is important when entering into dyntick-idle > mode -- if there are no further scheduling-clock interrupts, the callbacks > might never be invoked, which could result in a system hang. > > However, processing callbacks does event tracing, which in turn > implies RCU read-side critical sections, which are illegal in extended > quiescent states. This patch therefore moves the call to rcu_sched_qs() > so that it precedes the point at which we set the new value of > rcu_dynticks_nesting, which may indicate RCU is in an extended quiescent > state.
Thank you, Zhong. Queued, as those checking the SOBs below might guess. ;-)
Thanx, paul
> Signed-off-by: Li Zhong <zhong@linux.vnet.ibm.com> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > --- > kernel/rcutiny.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c > index 2e073a2..e4c6a59 100644 > --- a/kernel/rcutiny.c > +++ b/kernel/rcutiny.c > @@ -75,9 +75,9 @@ static void rcu_idle_enter_common(long long newval) > current->pid, current->comm, > idle->pid, idle->comm); /* must be idle task! */ > } > + rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ > barrier(); > rcu_dynticks_nesting = newval; > - rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ > } > > /* > -- > 1.7.9.5 > > >
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