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Message-ID: <4B1B6F87.6050201@gmail.com>
Date: Sun, 06 Dec 2009 09:47:03 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: Jarek Poplawski <jarkao2@...il.com>
CC: "David S. Miller" <davem@...emloft.net>,
Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [PATCH] inetpeer: optimizations
Jarek Poplawski a écrit :
> Eric Dumazet wrote, On 12/05/2009 01:11 PM:
>
>> - Use atomic_dec_and_test() in inet_putpeer()
>
> atomic_dec_and_lock()?
Yes :)
>
>> This takes/dirties the lock only if necessary.
> ...
>
>> void inet_putpeer(struct inet_peer *p)
>> {
>> - spin_lock_bh(&inet_peer_unused_lock);
>> - if (atomic_dec_and_test(&p->refcnt)) {
>> - list_add_tail(&p->unused, &unused_peers);
>> + local_bh_disable();
>> + if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) {
>
> Why not:
> if (atomic_dec_and_test(&p->refcnt)) {
> spin_lock_bh(&inet_peer_unused_lock);
> ...
Because we have to take the lock before doing the final 1 -> 0 refcount transition.
(Another thread could do the 0 -> 1 transition)
I'll cook a followup patch to also avoid taking the lock in the 1+ -> 2+ transitions.
Thanks
[PATCH] inetpeer: optimizations
- Use atomic_dec_and_lock() in inet_putpeer()
This takes/dirties the lock only if necessary.
- Group fields together, since they currently are in BSS and DATA section,
we have to dirty two cache lines instead of one.
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
net/ipv4/inetpeer.c | 78 ++++++++++++++++++++++++------------------
1 file changed, 45 insertions(+), 33 deletions(-)
diff --git a/net/ipv4/inetpeer.c b/net/ipv4/inetpeer.c
index 6bcfe52..4125ef9 100644
--- a/net/ipv4/inetpeer.c
+++ b/net/ipv4/inetpeer.c
@@ -76,11 +76,17 @@ static struct inet_peer peer_fake_node = {
.avl_height = 0
};
#define peer_avl_empty (&peer_fake_node)
-static struct inet_peer *peer_root = peer_avl_empty;
-static DEFINE_RWLOCK(peer_pool_lock);
+
+static struct {
+ struct inet_peer *root;
+ rwlock_t lock;
+ int total;
+} peers = {
+ .root = peer_avl_empty,
+ .lock = __RW_LOCK_UNLOCKED(peers.lock),
+};
#define PEER_MAXDEPTH 40 /* sufficient for about 227 nodes */
-static int peer_total;
/* Exported for sysctl_net_ipv4. */
int inet_peer_threshold __read_mostly = 65536 + 128; /* start to throw entries more
* aggressively at this stage */
@@ -89,8 +95,13 @@ int inet_peer_maxttl __read_mostly = 10 * 60 * HZ; /* usual time to live: 10 min
int inet_peer_gc_mintime __read_mostly = 10 * HZ;
int inet_peer_gc_maxtime __read_mostly = 120 * HZ;
-static LIST_HEAD(unused_peers);
-static DEFINE_SPINLOCK(inet_peer_unused_lock);
+static struct {
+ struct list_head list;
+ spinlock_t lock;
+} unused_peers = {
+ .list = LIST_HEAD_INIT(unused_peers.list),
+ .lock = __SPIN_LOCK_UNLOCKED(unused_peers.lock),
+};
static void peer_check_expire(unsigned long dummy);
static DEFINE_TIMER(peer_periodic_timer, peer_check_expire, 0, 0);
@@ -131,9 +142,9 @@ void __init inet_initpeers(void)
/* Called with or without local BH being disabled. */
static void unlink_from_unused(struct inet_peer *p)
{
- spin_lock_bh(&inet_peer_unused_lock);
+ spin_lock_bh(&unused_peers.lock);
list_del_init(&p->unused);
- spin_unlock_bh(&inet_peer_unused_lock);
+ spin_unlock_bh(&unused_peers.lock);
}
/*
@@ -146,9 +157,9 @@ static void unlink_from_unused(struct inet_peer *p)
struct inet_peer *u, **v; \
if (_stack != NULL) { \
stackptr = _stack; \
- *stackptr++ = &peer_root; \
+ *stackptr++ = &peers.root; \
} \
- for (u = peer_root; u != peer_avl_empty; ) { \
+ for (u = peers.root; u != peer_avl_empty; ) { \
if (_daddr == u->v4daddr) \
break; \
if ((__force __u32)_daddr < (__force __u32)u->v4daddr) \
@@ -262,7 +273,7 @@ do { \
n->avl_right = peer_avl_empty; \
**--stackptr = n; \
peer_avl_rebalance(stack, stackptr); \
-} while(0)
+} while (0)
/* May be called with local BH enabled. */
static void unlink_from_pool(struct inet_peer *p)
@@ -271,7 +282,7 @@ static void unlink_from_pool(struct inet_peer *p)
do_free = 0;
- write_lock_bh(&peer_pool_lock);
+ write_lock_bh(&peers.lock);
/* Check the reference counter. It was artificially incremented by 1
* in cleanup() function to prevent sudden disappearing. If the
* reference count is still 1 then the node is referenced only as `p'
@@ -303,10 +314,10 @@ static void unlink_from_pool(struct inet_peer *p)
delp[1] = &t->avl_left; /* was &p->avl_left */
}
peer_avl_rebalance(stack, stackptr);
- peer_total--;
+ peers.total--;
do_free = 1;
}
- write_unlock_bh(&peer_pool_lock);
+ write_unlock_bh(&peers.lock);
if (do_free)
kmem_cache_free(peer_cachep, p);
@@ -326,16 +337,16 @@ static int cleanup_once(unsigned long ttl)
struct inet_peer *p = NULL;
/* Remove the first entry from the list of unused nodes. */
- spin_lock_bh(&inet_peer_unused_lock);
- if (!list_empty(&unused_peers)) {
+ spin_lock_bh(&unused_peers.lock);
+ if (!list_empty(&unused_peers.list)) {
__u32 delta;
- p = list_first_entry(&unused_peers, struct inet_peer, unused);
+ p = list_first_entry(&unused_peers.list, struct inet_peer, unused);
delta = (__u32)jiffies - p->dtime;
if (delta < ttl) {
/* Do not prune fresh entries. */
- spin_unlock_bh(&inet_peer_unused_lock);
+ spin_unlock_bh(&unused_peers.lock);
return -1;
}
@@ -345,7 +356,7 @@ static int cleanup_once(unsigned long ttl)
* before unlink_from_pool() call. */
atomic_inc(&p->refcnt);
}
- spin_unlock_bh(&inet_peer_unused_lock);
+ spin_unlock_bh(&unused_peers.lock);
if (p == NULL)
/* It means that the total number of USED entries has
@@ -364,11 +375,11 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
struct inet_peer **stack[PEER_MAXDEPTH], ***stackptr;
/* Look up for the address quickly. */
- read_lock_bh(&peer_pool_lock);
+ read_lock_bh(&peers.lock);
p = lookup(daddr, NULL);
if (p != peer_avl_empty)
atomic_inc(&p->refcnt);
- read_unlock_bh(&peer_pool_lock);
+ read_unlock_bh(&peers.lock);
if (p != peer_avl_empty) {
/* The existing node has been found. */
@@ -390,7 +401,7 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
atomic_set(&n->ip_id_count, secure_ip_id(daddr));
n->tcp_ts_stamp = 0;
- write_lock_bh(&peer_pool_lock);
+ write_lock_bh(&peers.lock);
/* Check if an entry has suddenly appeared. */
p = lookup(daddr, stack);
if (p != peer_avl_empty)
@@ -399,10 +410,10 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
/* Link the node. */
link_to_pool(n);
INIT_LIST_HEAD(&n->unused);
- peer_total++;
- write_unlock_bh(&peer_pool_lock);
+ peers.total++;
+ write_unlock_bh(&peers.lock);
- if (peer_total >= inet_peer_threshold)
+ if (peers.total >= inet_peer_threshold)
/* Remove one less-recently-used entry. */
cleanup_once(0);
@@ -411,7 +422,7 @@ struct inet_peer *inet_getpeer(__be32 daddr, int create)
out_free:
/* The appropriate node is already in the pool. */
atomic_inc(&p->refcnt);
- write_unlock_bh(&peer_pool_lock);
+ write_unlock_bh(&peers.lock);
/* Remove the entry from unused list if it was there. */
unlink_from_unused(p);
/* Free preallocated the preallocated node. */
@@ -425,12 +436,12 @@ static void peer_check_expire(unsigned long dummy)
unsigned long now = jiffies;
int ttl;
- if (peer_total >= inet_peer_threshold)
+ if (peers.total >= inet_peer_threshold)
ttl = inet_peer_minttl;
else
ttl = inet_peer_maxttl
- (inet_peer_maxttl - inet_peer_minttl) / HZ *
- peer_total / inet_peer_threshold * HZ;
+ peers.total / inet_peer_threshold * HZ;
while (!cleanup_once(ttl)) {
if (jiffies != now)
break;
@@ -439,22 +450,23 @@ static void peer_check_expire(unsigned long dummy)
/* Trigger the timer after inet_peer_gc_mintime .. inet_peer_gc_maxtime
* interval depending on the total number of entries (more entries,
* less interval). */
- if (peer_total >= inet_peer_threshold)
+ if (peers.total >= inet_peer_threshold)
peer_periodic_timer.expires = jiffies + inet_peer_gc_mintime;
else
peer_periodic_timer.expires = jiffies
+ inet_peer_gc_maxtime
- (inet_peer_gc_maxtime - inet_peer_gc_mintime) / HZ *
- peer_total / inet_peer_threshold * HZ;
+ peers.total / inet_peer_threshold * HZ;
add_timer(&peer_periodic_timer);
}
void inet_putpeer(struct inet_peer *p)
{
- spin_lock_bh(&inet_peer_unused_lock);
- if (atomic_dec_and_test(&p->refcnt)) {
- list_add_tail(&p->unused, &unused_peers);
+ local_bh_disable();
+ if (atomic_dec_and_lock(&p->refcnt, &unused_peers.lock)) {
+ list_add_tail(&p->unused, &unused_peers.list);
p->dtime = (__u32)jiffies;
+ spin_unlock(&unused_peers.lock);
}
- spin_unlock_bh(&inet_peer_unused_lock);
+ local_bh_enable();
}
--
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