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    SubjectRe: [PATCH tip/core/rcu 13/15] rcu: Introduce for_each_rcu_flavor() and use it
    On Fri, Jun 15, 2012 at 04:52:40PM -0700, Josh Triplett wrote:
    > On Fri, Jun 15, 2012 at 02:06:08PM -0700, Paul E. McKenney wrote:
    > > From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
    > >
    > > The arrival of TREE_PREEMPT_RCU some years back included some ugly
    > > code involving either #ifdef or #ifdef'ed wrapper functions to iterate
    > > over all non-SRCU flavors of RCU. This commit therefore introduces
    > > a for_each_rcu_flavor() iterator over the rcu_state structures for each
    > > flavor of RCU to clean up a bit of the ugliness.
    > >
    > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    >
    > Great cleanup!
    >
    > A few comments below, though.
    >
    > > kernel/rcutree.c | 53 +++++++++++++---------
    > > kernel/rcutree.h | 12 ++---
    > > kernel/rcutree_plugin.h | 116 -----------------------------------------------
    > > 3 files changed, 36 insertions(+), 145 deletions(-)
    >
    > Awesome diffstat.

    ;-)

    > > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    > > index bd4e41c..75ad92a 100644
    > > --- a/kernel/rcutree.c
    > > +++ b/kernel/rcutree.c
    > > @@ -84,6 +84,7 @@ struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh, call_rcu_bh);
    > > DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
    > >
    > > static struct rcu_state *rcu_state;
    > > +LIST_HEAD(rcu_struct_flavors);
    >
    > Does any means exist to turn this into a constant array known at compile
    > time rather than a runtime linked list? Having this as a compile-time
    > constant may allow the compiler to unroll for_each_rcu_flavor and
    > potentially inline the calls inside it.

    I could do that, but none of the traversals is anywhere near performance
    critical, and all the ways I can think of to do this are uglier than
    the list.

    > > @@ -2539,9 +2548,10 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
    > >
    > > static void __cpuinit rcu_prepare_cpu(int cpu)
    > > {
    > > - rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
    > > - rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
    > > - rcu_preempt_init_percpu_data(cpu);
    > > + struct rcu_state *rsp;
    > > +
    > > + for_each_rcu_flavor(rsp)
    > > + rcu_init_percpu_data(cpu, rsp, 0);
    >
    > This results in passing 0 as the "preemptible" parameter of
    > rcu_init_percpu_data, which seems wrong if the preemptible parameter has
    > any meaning at all. :)

    Good catch! Hmmm... Probably best to move this to the rcu_state
    initialization.

    > > @@ -2577,18 +2588,15 @@ static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
    > > * touch any data without introducing corruption. We send the
    > > * dying CPU's callbacks to an arbitrarily chosen online CPU.
    > > */
    > > - rcu_cleanup_dying_cpu(&rcu_bh_state);
    > > - rcu_cleanup_dying_cpu(&rcu_sched_state);
    > > - rcu_preempt_cleanup_dying_cpu();
    > > - rcu_cleanup_after_idle(cpu);
    > > + for_each_rcu_flavor(rsp)
    > > + rcu_cleanup_dying_cpu(rsp);
    >
    > Why did rcu_cleanup_after_idle go away here?

    Because I fat-fingered it. Thank you very much for spotting this. It
    would have been nasty to find otherwise.

    Thanx, Paul



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