From: "Paul E. McKenney" Subject: Re: [PATCH 09/10] cfq-iosched: Uses its own open-coded rcu_barrier. Date: Wed, 24 Jun 2009 07:05:05 -0700 Message-ID: <20090624140505.GA6779@linux.vnet.ibm.com> References: <20090623150330.22490.87327.stgit@localhost> <20090623150439.22490.14657.stgit@localhost> <20090624064236.GE31415@kernel.dk> Reply-To: paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jesper Dangaard Brouer , "David S. Miller" , netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, dougthompson-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org, bluesmoke-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, Patrick McHardy , christine.caulfield-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org, Trond.Myklebust-HgOvQuBEEgTQT0dZR+AlfA@public.gmane.org, linux-wireless-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, johannes-cdvu00un1VgdHxzADdlk8Q@public.gmane.org, yoshfuji-VfPWfsRibaP+Ru+s062T9g@public.gmane.org, shemminger-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org, linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org, neilb-l3A5Bk7waGM@public.gmane.org, linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, tytso-3s7WtUTddSA@public.gmane.org, adilger-xsfywfwIY+M@public.gmane.org, netfilter-devel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jens Axboe Return-path: Content-Disposition: inline In-Reply-To: <20090624064236.GE31415-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org> Sender: linux-nfs-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-ext4.vger.kernel.org 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 > > --- > > > > 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-4UpuNZONu4c@public.gmane.org 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-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html