Message ID | 20090623150439.22490.14657.stgit@localhost |
---|---|
State | Not Applicable, archived |
Delegated to: | David Miller |
Headers | show |
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); >
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@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 > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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);
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. Signed-off-by: Jesper Dangaard Brouer <hawk@comx.dk> --- block/cfq-iosched.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html