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netfilter: x_tables: dont block BH while reading counters

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Using "iptables -L" with a lot of rules have a too big BH latency.
Jesper mentioned ~6 ms and worried of frame drops.

Switch to a per_cpu seqlock scheme, so that taking a snapshot of
counters doesnt need to block BH (for this cpu, but also other cpus).

This adds two increments on seqlock sequence per ipt_do_table() call,
its a reasonable cost for allowing "iptables -L" not block BH
processing.

Reported-by: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Jesper Dangaard Brouer <hawk@comx.dk>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Eric Dumazet
2011-01-10 20:11:38 +01:00
committed by Pablo Neira Ayuso
parent 45b9f509b7
commit 83723d6071
5 changed files with 49 additions and 99 deletions
Download Patch File Download Diff File Expand all files Collapse all files

10
include/linux/netfilter/x_tables.h
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@@ -472,7 +472,7 @@ extern void xt_free_table_info(struct xt_table_info *info);
* necessary for reading the counters.
*/
struct xt_info_lock {
spinlock_t lock;
seqlock_t lock;
unsigned char readers;
};
DECLARE_PER_CPU(struct xt_info_lock, xt_info_locks);
@@ -497,7 +497,7 @@ static inline void xt_info_rdlock_bh(void)
local_bh_disable();
lock = &__get_cpu_var(xt_info_locks);
if (likely(!lock->readers++))
spin_lock(&lock->lock);
write_seqlock(&lock->lock);
}
static inline void xt_info_rdunlock_bh(void)
@@ -505,7 +505,7 @@ static inline void xt_info_rdunlock_bh(void)
struct xt_info_lock *lock = &__get_cpu_var(xt_info_locks);
if (likely(!--lock->readers))
spin_unlock(&lock->lock);
write_sequnlock(&lock->lock);
local_bh_enable();
}
@@ -516,12 +516,12 @@ static inline void xt_info_rdunlock_bh(void)
*/
static inline void xt_info_wrlock(unsigned int cpu)
{
spin_lock(&per_cpu(xt_info_locks, cpu).lock);
write_seqlock(&per_cpu(xt_info_locks, cpu).lock);
}
static inline void xt_info_wrunlock(unsigned int cpu)
{
spin_unlock(&per_cpu(xt_info_locks, cpu).lock);
write_sequnlock(&per_cpu(xt_info_locks, cpu).lock);
}
/*