linux-ext4 - [PATCH 09/10] cfq-iosched: Uses its own open-coded rcu

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Message-ID: <20090623150439.22490.14657.stgit@localhost>
Date:	Tue, 23 Jun 2009 17:04:39 +0200
From:	Jesper Dangaard Brouer <hawk@...x.dk>
To:	"David S. Miller" <davem@...emloft.net>
Cc:	Jesper Dangaard Brouer <hawk@...x.dk>,
	"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,
	axboe@...nel.dk, "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: [PATCH 09/10] cfq-iosched: Uses its own open-coded rcu_barrier.

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@...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);

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