Re: [PATCH] netfilter: use per-CPU recursive lock {XIV}

Stephen Hemminger
2009-04-24T16:19:04Z

On Fri, 24 Apr 2009 06:58:39 +0200
Eric Dumazet <dada1@cosmosbay.com> wrote:

> Stephen Hemminger a écrit :
> > In days of old in 2.6.29, netfilter did locketh using a
> > lock of the reader kind when doing its table business, and do
> > a writer when with pen in hand like a overworked accountant
> > did replace the tables. This sucketh and caused the single
> > lock to fly back and forth like a poor errant boy.
> >
> > But then netfilter was blessed with RCU and the performance
> > was divine, but alas there were those that suffered for
> > trying to replace their many rules one at a time.
> >
> > So now RCU must be vanquished from the scene, and better
> > chastity belts be placed upon this valuable asset most dear.
> > The locks that were but one are now replaced by one per suitor.
> >
> > The repair was made after much discussion involving
> > Eric the wise, and Linus the foul. With flowers springing
> > up amid the thorns some peace has finally prevailed and
> > all is soothed. This patch and purple prose was penned by
> > in honor of "Talk like Shakespeare" day.
> >
> > Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>
>
> Philip Davis of the university’s School of English said :
>
> "Shakespeare surprises the brain and catches it off guard in
> a manner that produces a sudden burst of activity - a sense
> of drama created out of the simplest of things."
>
> http://www.physorg.com/news85664210.html
>
> >
> > ---
> > What hath changed over the last two setting suns:
> > * more words, mostly correct...
> >
> > * no need to locketh for writeh on current cpu tis
> > always so
> >
> > * the locking of all cpu's on replace is always done as
> > part of the get_counters cycle, so the sychronize swip
> > in replace tables is gone with only a comment remaing
> >
> > include/linux/netfilter/x_tables.h | 55 ++++++++++++++--
> > net/ipv4/netfilter/arp_tables.c | 125 ++++++++++--------------------------
> > net/ipv4/netfilter/ip_tables.c | 126 ++++++++++---------------------------
> > net/ipv6/netfilter/ip6_tables.c | 123 ++++++++++--------------------------
> > net/netfilter/x_tables.c | 55 ++++++++--------
> > 5 files changed, 188 insertions(+), 296 deletions(-)
> >
>
>
> >
> > static int __init xt_init(void)
> > {
> > - int i, rv;
> > + unsigned int i;
> > + int rv;
> > + static struct lock_class_key xt_lock_key[NR_CPUS];
>
> Could we avoid this [NR_CPUS] thing ?
>
> > +
> > + for_each_possible_cpu(i) {
> > + rwlock_t *lock = &per_cpu(xt_info_locks, i);
> > +
> > + rwlock_init(lock);
> > + lockdep_set_class(lock, xt_lock_key+i);
> > + }
>
>
> Did you tried :
>
> static DECLARE_PER_CPU(struct lock_class_key, xt_locks_key);
>

The lock keys are really only used by lock dep, and I thought per cpu
space was more scarce on some arch.