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Date: Tue, 08 Jun 2010 17:12:26 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: Patrick McHardy <kaber@...sh.net>
Cc: Changli Gao <xiaosuo@...il.com>,
Netfilter Developers <netfilter-devel@...r.kernel.org>,
netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH nf-next-2.6 2/2] conntrack: per_cpu untracking
Le mardi 08 juin 2010 à 16:52 +0200, Eric Dumazet a écrit :
> Le mardi 08 juin 2010 à 16:29 +0200, Patrick McHardy a écrit :
> > On 04.06.2010 22:15, Eric Dumazet wrote:
> > > NOTRACK makes all cpus share a cache line on nf_conntrack_untracked
> > > twice per packet, slowing down performance.
> > >
> > > This patch converts it to a per_cpu variable.
> > >
> > > We assume same cpu is used for a given packet, entering and exiting the
> > > NOTRACK state.
> >
> > That doesn't seem to be a valid assumption, the conntrack entry is
> > attached to the skb and processing in the output path might get
> > preempted and rescheduled to a different CPU.
>
> Thats unfortunate.
>
> Ok, only choice then is to not change refcount on the untracked ct, and
> keep a shared (read only after setup time) untrack structure.
>
>
Oh well, re-reading my patch, I dont see why I said this in Changelog :)
We lazily select the untrack structure in one cpu, then keep the pointer
to this untrack structure, attached to ct.
The (still atomic) increment / decrement of refcount is done on the
saved pointer, not on actual per_cpu structure.
So if a packet is rescheduled on a different CPU, second cpu will "only"
dirty cache line of other cpu, it probably almost never happens...
Thanks
[PATCH nf-next-2.6 2/2] conntrack: per_cpu untracking
NOTRACK makes all cpus share a cache line on nf_conntrack_untracked
twice per packet, slowing down performance.
This patch converts it to a per_cpu variable.
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
include/net/netfilter/nf_conntrack.h | 5 +--
net/netfilter/nf_conntrack_core.c | 36 ++++++++++++++++++-------
2 files changed, 28 insertions(+), 13 deletions(-)
diff --git a/include/net/netfilter/nf_conntrack.h b/include/net/netfilter/nf_conntrack.h
index 3bc38c7..84a4b6f 100644
--- a/include/net/netfilter/nf_conntrack.h
+++ b/include/net/netfilter/nf_conntrack.h
@@ -261,11 +261,10 @@ extern s16 (*nf_ct_nat_offset)(const struct nf_conn *ct,
u32 seq);
/* Fake conntrack entry for untracked connections */
+DECLARE_PER_CPU(struct nf_conn, nf_conntrack_untracked);
static inline struct nf_conn *nf_ct_untracked_get(void)
{
- extern struct nf_conn nf_conntrack_untracked;
-
- return &nf_conntrack_untracked;
+ return &__raw_get_cpu_var(nf_conntrack_untracked);
}
extern void nf_ct_untracked_status_or(unsigned long bits);
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 6c1da21..9c66141 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -62,8 +62,8 @@ EXPORT_SYMBOL_GPL(nf_conntrack_htable_size);
unsigned int nf_conntrack_max __read_mostly;
EXPORT_SYMBOL_GPL(nf_conntrack_max);
-struct nf_conn nf_conntrack_untracked;
-EXPORT_SYMBOL_GPL(nf_conntrack_untracked);
+DEFINE_PER_CPU(struct nf_conn, nf_conntrack_untracked);
+EXPORT_PER_CPU_SYMBOL(nf_conntrack_untracked);
static int nf_conntrack_hash_rnd_initted;
static unsigned int nf_conntrack_hash_rnd;
@@ -1183,10 +1183,21 @@ static void nf_ct_release_dying_list(struct net *net)
spin_unlock_bh(&nf_conntrack_lock);
}
+static int untrack_refs(void)
+{
+ int cnt = 0, cpu;
+
+ for_each_possible_cpu(cpu) {
+ struct nf_conn *ct = &per_cpu(nf_conntrack_untracked, cpu);
+
+ cnt += atomic_read(&ct->ct_general.use) - 1;
+ }
+ return cnt;
+}
+
static void nf_conntrack_cleanup_init_net(void)
{
- /* wait until all references to nf_conntrack_untracked are dropped */
- while (atomic_read(&nf_conntrack_untracked.ct_general.use) > 1)
+ while (untrack_refs() > 0)
schedule();
nf_conntrack_helper_fini();
@@ -1323,14 +1334,17 @@ module_param_call(hashsize, nf_conntrack_set_hashsize, param_get_uint,
void nf_ct_untracked_status_or(unsigned long bits)
{
- nf_conntrack_untracked.status |= bits;
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ per_cpu(nf_conntrack_untracked, cpu).status |= bits;
}
EXPORT_SYMBOL_GPL(nf_ct_untracked_status_or);
static int nf_conntrack_init_init_net(void)
{
int max_factor = 8;
- int ret;
+ int ret, cpu;
/* Idea from tcp.c: use 1/16384 of memory. On i386: 32MB
* machine has 512 buckets. >= 1GB machines have 16384 buckets. */
@@ -1369,10 +1383,12 @@ static int nf_conntrack_init_init_net(void)
goto err_extend;
#endif
/* Set up fake conntrack: to never be deleted, not in any hashes */
-#ifdef CONFIG_NET_NS
- nf_conntrack_untracked.ct_net = &init_net;
-#endif
- atomic_set(&nf_conntrack_untracked.ct_general.use, 1);
+ for_each_possible_cpu(cpu) {
+ struct nf_conn *ct = &per_cpu(nf_conntrack_untracked, cpu);
+
+ write_pnet(&ct->ct_net, &init_net);
+ atomic_set(&ct->ct_general.use, 1);
+ }
/* - and look it like as a confirmed connection */
nf_ct_untracked_status_or(IPS_CONFIRMED | IPS_UNTRACKED);
return 0;
--
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