Patchwork [net-next-2.6] phonet: use call_rcu for phonet device free

login
register
mail settings
Submitter Jiri Pirko
Date June 7, 2010, 1:27 p.m.
Message ID <20100607132738.GB2730@psychotron.lab.eng.brq.redhat.com>
Download mbox | patch
Permalink /patch/54854/
State Accepted
Delegated to: David Miller
Headers show

Comments

Jiri Pirko - June 7, 2010, 1:27 p.m.
Use call_rcu rather than synchronize_rcu.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
---
 include/net/phonet/pn_dev.h |    1 +
 net/phonet/pn_dev.c         |   15 +++++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)
Rémi Denis-Courmont - June 7, 2010, 1:43 p.m.
On Mon, 7 Jun 2010 15:27:39 +0200, Jiri Pirko <jpirko@redhat.com> wrote:
> Use call_rcu rather than synchronize_rcu.
> 
> Signed-off-by: Jiri Pirko <jpirko@redhat.com>

This looks fine to me, but what is the goal here? The RCU documentation
seems to imply that synchronize_rcu() is preferable over call_rcu() when at
all possible.
Eric Dumazet - June 7, 2010, 1:49 p.m.
Le lundi 07 juin 2010 à 15:43 +0200, Rémi Denis-Courmont a écrit :
> On Mon, 7 Jun 2010 15:27:39 +0200, Jiri Pirko <jpirko@redhat.com> wrote:
> > Use call_rcu rather than synchronize_rcu.
> > 
> > Signed-off-by: Jiri Pirko <jpirko@redhat.com>
> 
> This looks fine to me, but what is the goal here? The RCU documentation
> seems to imply that synchronize_rcu() is preferable over call_rcu() when at
> all possible.
> 

Thats not exactly that.

synchronize_rcu() is easier, in respect of memory use.
But its drawback is current thread is blocked for several milli seconds.

In the end, call_rcu() is more scalable.

Acked-by: Eric Dumazet <eric.dumazet@gmail.com>


--
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
David Miller - June 9, 2010, 11:15 p.m.
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 07 Jun 2010 15:49:43 +0200

> Le lundi 07 juin 2010 à 15:43 +0200, Rémi Denis-Courmont a écrit :
>> On Mon, 7 Jun 2010 15:27:39 +0200, Jiri Pirko <jpirko@redhat.com> wrote:
>> > Use call_rcu rather than synchronize_rcu.
>> > 
>> > Signed-off-by: Jiri Pirko <jpirko@redhat.com>
>> 
>> This looks fine to me, but what is the goal here? The RCU documentation
>> seems to imply that synchronize_rcu() is preferable over call_rcu() when at
>> all possible.
>> 
> 
> Thats not exactly that.
> 
> synchronize_rcu() is easier, in respect of memory use.
> But its drawback is current thread is blocked for several milli seconds.
> 
> In the end, call_rcu() is more scalable.
> 
> Acked-by: Eric Dumazet <eric.dumazet@gmail.com>

Applied, thanks.
--
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

Patch

diff --git a/include/net/phonet/pn_dev.h b/include/net/phonet/pn_dev.h
index d7b989c..2d16783 100644
--- a/include/net/phonet/pn_dev.h
+++ b/include/net/phonet/pn_dev.h
@@ -34,6 +34,7 @@  struct phonet_device {
 	struct list_head list;
 	struct net_device *netdev;
 	DECLARE_BITMAP(addrs, 64);
+	struct rcu_head	rcu;
 };
 
 int phonet_device_init(void);
diff --git a/net/phonet/pn_dev.c b/net/phonet/pn_dev.c
index c33da65..b18e48f 100644
--- a/net/phonet/pn_dev.c
+++ b/net/phonet/pn_dev.c
@@ -162,6 +162,14 @@  int phonet_address_add(struct net_device *dev, u8 addr)
 	return err;
 }
 
+static void phonet_device_rcu_free(struct rcu_head *head)
+{
+	struct phonet_device *pnd;
+
+	pnd = container_of(head, struct phonet_device, rcu);
+	kfree(pnd);
+}
+
 int phonet_address_del(struct net_device *dev, u8 addr)
 {
 	struct phonet_device_list *pndevs = phonet_device_list(dev_net(dev));
@@ -179,10 +187,9 @@  int phonet_address_del(struct net_device *dev, u8 addr)
 		pnd = NULL;
 	mutex_unlock(&pndevs->lock);
 
-	if (pnd) {
-		synchronize_rcu();
-		kfree(pnd);
-	}
+	if (pnd)
+		call_rcu(&pnd->rcu, phonet_device_rcu_free);
+
 	return err;
 }