Subject: Re: [PATCH] netfilter: use per-cpu recursive lock (v13)

From: Eric Dumazet <[email-masked]>
Date: Wed, 22 Apr 2009 16:57:02 +0200

Stephen Hemminger a écrit :
> This version of x_tables (ip/ip6/arp) locking uses a per-cpu
> recursive lock that can be nested.
> 
> The idea for this came from an earlier version done by Eric Dumazet.
> Locking is done per-cpu, the fast path locks on the current cpu
> and updates counters.  This reduces the contention of a
> single reader lock (in 2.6.29) without the delay of synchronize_net()
> (in 2.6.30-rc2). 
> 
> 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.
> 
> Signed-off-by: Stephen Hemminger <[email-masked]

Signed-off-by: Eric Dumazet <[email-masked]>

Tested today on various machines and no problem so far
tbench/oprofile results, 3.7236% cpu spent in ipt_do_table, and 0.84% used
on read_lock/read_unlock

c04a5c30 <ipt_do_table>: /* ipt_do_table total: 217134  3.7236 */
...
   349  0.0060 :c04a5ccc:   call   c04ce380 <_read_lock>
 23914  0.4101 :c04a5cd1:   mov    0xc(%edi),%eax
...
               :c04a5ecb:   call   c04ce5f0 <_read_unlock_bh>
 25279  0.4335 :c04a5ed0:   cmpb   $0x0,-0xd(%ebp)

"iptables -L" fetches its data very fast too.
150 us on a 8 cpus machine, small firewall rules.
400-700 us on same machine, 1000 fw rules set (160000 bytes per cpu)
 depending on network trafic (from light to flood)

Thanks

> 
> ---
> CHANGES 
>   - reader and write now inline
>   - only acquire one cpu write lock at a time
>   - write lock pushed down into get_counters
> 
>  include/linux/netfilter/x_tables.h |   50 +++++++++++++--
>  net/ipv4/netfilter/arp_tables.c    |  121 ++++++++++---------------------------
>  net/ipv4/netfilter/ip_tables.c     |  120 +++++++++---------------------------
>  net/ipv6/netfilter/ip6_tables.c    |  120 ++++++++++--------------------------
>  net/netfilter/x_tables.c           |   55 +++++++++-------
>  5 files changed, 174 insertions(+), 292 deletions(-)
>