| Date | Tue, 16 Aug 2011 13:20:05 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 22/32] rcu: Restart tick if we enqueue a callback in a nohz/cpuset CPU |
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On Mon, Aug 15, 2011 at 05:52:19PM +0200, Frederic Weisbecker wrote: > If we enqueue an rcu callback, we need the CPU tick to stay > alive until we take care of those by completing the appropriate > grace period. > > Thus, when we call_rcu(), send a self IPI that checks rcu_needs_cpu() > so that we restore a periodic tick behaviour that can take care of > everything.
One question below.
Thanx, Paul
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Anton Blanchard <anton@au1.ibm.com> > Cc: Avi Kivity <avi@redhat.com> > Cc: Ingo Molnar <mingo@elte.hu> > Cc: Lai Jiangshan <laijs@cn.fujitsu.com> > Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com> > Cc: Paul Menage <menage@google.com> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> > Cc: Stephen Hemminger <shemminger@vyatta.com> > Cc: Thomas Gleixner <tglx@linutronix.de> > Cc: Tim Pepper <lnxninja@linux.vnet.ibm.com> > --- > kernel/rcutree.c | 8 ++++++++ > 1 files changed, 8 insertions(+), 0 deletions(-) > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c > index d496c70..b5643ce2 100644 > --- a/kernel/rcutree.c > +++ b/kernel/rcutree.c > @@ -51,6 +51,7 @@ > #include <linux/kthread.h> > #include <linux/prefetch.h> > #include <linux/cpuset.h> > +#include <linux/tick.h> > > #include "rcutree.h" > > @@ -1546,6 +1547,13 @@ __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), > rdp->nxttail[RCU_NEXT_TAIL] = &head->next; > rdp->qlen++; > > + /* Restart the timer if needed to handle the callbacks */ > + if (tick_nohz_adaptive_mode()) { > + /* Make updates on nxtlist visible to self IPI */ > + barrier(); > + smp_cpuset_update_nohz(smp_processor_id()); > + } > +
But this must be happening in a system call or interrupt handler, right? If so, won't we get a chance to check things on exit from the system call or interrupt? Or are you hooking only into syscall entry?
> /* If interrupts were disabled, don't dive into RCU core. */ > if (irqs_disabled_flags(flags)) { > local_irq_restore(flags); > -- > 1.7.5.4 >
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