netfilter: iptables: lock free counters
The reader/writer lock in ip_tables is acquired in the critical path of
processing packets and is one of the reasons just loading iptables can cause
a 20% performance loss. The rwlock serves two functions:
1) it prevents changes to table state (xt_replace) while table is in use.
This is now handled by doing rcu on the xt_table. When table is
replaced, the new table(s) are put in and the old one table(s) are freed
after RCU period.
2) it provides synchronization when accesing the counter values.
This is now handled by swapping in new table_info entries for each cpu
then summing the old values, and putting the result back onto one
cpu. On a busy system it may cause sampling to occur at different
times on each cpu, but no packet/byte counts are lost in the process.
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Sucessfully tested on my dual quad core machine too, but iptables only (no ipv6 here)
BTW, my new "tbench 8" result is 2450 MB/s, (it was 2150 MB/s not so long ago)
Acked-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/include/linux/netfilter/x_tables.h b/include/linux/netfilter/x_tables.h
index 9fac88f..e8e08d0 100644
--- a/include/linux/netfilter/x_tables.h
+++ b/include/linux/netfilter/x_tables.h
@@ -353,7 +353,7 @@
unsigned int valid_hooks;
/* Lock for the curtain */
- rwlock_t lock;
+ struct mutex lock;
/* Man behind the curtain... */
struct xt_table_info *private;
@@ -385,7 +385,7 @@
/* ipt_entry tables: one per CPU */
/* Note : this field MUST be the last one, see XT_TABLE_INFO_SZ */
- char *entries[1];
+ void *entries[1];
};
#define XT_TABLE_INFO_SZ (offsetof(struct xt_table_info, entries) \
@@ -432,6 +432,8 @@
extern struct xt_table_info *xt_alloc_table_info(unsigned int size);
extern void xt_free_table_info(struct xt_table_info *info);
+extern void xt_table_entry_swap_rcu(struct xt_table_info *old,
+ struct xt_table_info *new);
#ifdef CONFIG_COMPAT
#include <net/compat.h>