On Tue, Jul 04, 2006 at 02:58:42PM +0200, Urs Thuermann wrote:
> Thomas Gleixner <[email protected]> writes:
>
> > Does Documentation/listRCU.txt answer your questions ?
>
> It doesn't answer my question. I have code that receives network
> packets by registering with dev_add_pack(). Each packet received is
> then delivered to a list of receivers, where this list can contain quite
> a lot of items:
>
> receive_function(struct sk_buff *skb, struct net_device *dev,
> struct packet_type *pt, struct net_device *orig_dev)
> {
> ...
> rcu_read_lock();
> head = find_list(dev);
> hlist_for_each_entry_rcu(p, n, head, list) {
> deliver_packet_to_receiver(skb, p);
> }
> rcu_read_unlock();
> }
>
> The deliver_packet_to_receiver() function finally ends up in a call to
> sock_queue_rcv_skb().
>
> My questions was, wether I should worry to "hold" the rcu_read_lock for
> the time of the list traversal since the list can be quite long and
> preemption is disabled between rcu_read_lock() and rcu_read_unlock().
"Holding" rcu_read_lock() for long time periods is much less of a
concern than holding other types of synchronization mechanisms.
The main concern is the effect on realtime latency in CONFIG_PREEMPT
(but -not- CONFIG_PREEMPT_RT) kernels. This concern is due to the
fact that rcu_read_lock() suppresses preemption in CONFIG_PREEMPT
kernels.
But I have to ask: roughly how long is "quite long"?
Thanx, Paul
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
