Messages in this thread |  | | Date | Wed, 24 Jun 2009 08:42:37 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH 09/10] cfq-iosched: Uses its own open-coded rcu_barrier. |
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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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