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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 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.

    > @@ -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. :)

    > @@ -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?

    - Josh Triplett


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