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Date: Wed, 24 Jun 2009 08:42:37 +0200 From: Jens Axboe <jens.axboe@...cle.com> To: Jesper Dangaard Brouer <hawk@...x.dk> Cc: "David S. Miller" <davem@...emloft.net>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, dougthompson@...ssion.com, bluesmoke-devel@...ts.sourceforge.net, Patrick McHardy <kaber@...sh.net>, christine.caulfield@...glemail.com, Trond.Myklebust@...app.com, linux-wireless@...r.kernel.org, johannes@...solutions.net, yoshfuji@...ux-ipv6.org, shemminger@...ux-foundation.org, linux-nfs@...r.kernel.org, bfields@...ldses.org, neilb@...e.de, linux-ext4@...r.kernel.org, tytso@....edu, adilger@....com, netfilter-devel@...r.kernel.org Subject: Re: [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@...x.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@...x.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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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