On Mon, 13 Apr 2009 16:20:00 -0700 Stephen Hemminger <shemminger@xxxxxxxxxx> wrote: > On Mon, 13 Apr 2009 15:24:37 -0700 > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > On Mon, 13 Apr 2009 09:53:09 -0700 > > Stephen Hemminger <shemminger@xxxxxxxxxx> wrote: > > > > > This is an alternative version of ip/ip6/arp tables locking using > > > per-cpu locks. This avoids the overhead of synchronize_net() during > > > update but still removes the expensive rwlock in earlier versions. > > > > > > The idea for this came from an earlier version done by Eric Duzamet. > > > Locking is done per-cpu, the fast path locks on the current cpu > > > and updates counters. The slow case involves acquiring the locks on > > > all cpu's. > > > > > > The mutex that was added for 2.6.30 in xt_table is unnecessary since > > > there already is a mutex for xt[af].mutex that is held. > > > > > > Tested basic functionality (add/remove/list), but don't have test cases > > > for stress, ip6tables or arptables. > > > > > > unsigned int > > > ipt_do_table(struct sk_buff *skb, > > > @@ -339,9 +341,10 @@ ipt_do_table(struct sk_buff *skb, > > > > > > IP_NF_ASSERT(table->valid_hooks & (1 << hook)); > > > > > > - rcu_read_lock_bh(); > > > - private = rcu_dereference(table->private); > > > - table_base = rcu_dereference(private->entries[smp_processor_id()]); > > > + local_bh_disable(); > > > + spin_lock(&__get_cpu_var(ip_tables_lock)); > > > > spin_lock_bh()? > > No. get_cpu_var implies smp_processor_id which is not safe > without preempt_disable (ie bh disable). spin_lock_bh() will dtrt, but spelling it out seems a good idea. It should have an explanatory comment, IMO. > > > > And it should be hotplug aware, really. num_possible_cpus() can exceed > > num_online_cpus(). The extent by which possible>online is > > controversial, but one can conceive of situations where it is "lots". > > It is doing right thing already with hotplug. It's slow. > This code still needs to count packets processed by previously online > cpu, that is no longer there. Those counts could be migrated off that CPU when it is offlined. As percpucounter does. > > Is lib/percpu_counter.c no good for this application? Unfixably no > > good? That code automagically handles cpu hotplug. > > percpu_counter can't deal with the layout/load here. Insufficient detail here for anyone to understand why percpucounter cannot be adapted to this requirement. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
