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    SubjectRe: [PATCH 09/10] cfq-iosched: Uses its own open-coded rcu_barrier.
    On Tue, Jun 23 2009, Jesper Dangaard Brouer wrote:
    > This module cfq-iosched, has discovered the value of waiting for
    > call_rcu() completion, but its has its own open-coded implementation
    > of rcu_barrier(), which I don't think is 'strong' enough.
    >
    > This patch only leaves a comment for the maintainers to consider.

    We need a stronger primitive and rcu_barrier(), since we also need to
    wait for the rcu calls to even be scheduled. So I don't think the below
    can be improved, it's already fine.

    >
    > Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk>
    > ---
    >
    > block/cfq-iosched.c | 6 ++++++
    > 1 files changed, 6 insertions(+), 0 deletions(-)
    >
    > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
    > index 833ec18..c15555b 100644
    > --- a/block/cfq-iosched.c
    > +++ b/block/cfq-iosched.c
    > @@ -2657,6 +2657,12 @@ static void __exit cfq_exit(void)
    > /*
    > * this also protects us from entering cfq_slab_kill() with
    > * pending RCU callbacks
    > + *
    > + * hawk@comx.dk 2009-06-18: Maintainer please consider using
    > + * rcu_barrier() instead of this open-coded wait for
    > + * completion implementation. I think it provides a better
    > + * guarantee that all CPUs are finished, although
    > + * elv_ioc_count_read() do consider all CPUs.
    > */
    > if (elv_ioc_count_read(ioc_count))
    > wait_for_completion(&all_gone);
    >

    --
    Jens Axboe



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