On Wed, Jun 24, 2009 at 08:42:37AM +0200, Jens Axboe wrote: > 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. It is indeed important to first prevent new call_rcu() instances from being invoked, and only then invoke rcu_barrier(). Thanx, Paul > > Signed-off-by: Jesper Dangaard Brouer <hawk@xxxxxxx> > > --- > > > > 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@xxxxxxx 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
