Re: [PATCH] INET : removes per bucket rwlock in tcp/dccp ehash table

[Eric Dumazet <dada1@cosmosbay.com>]

[-- Attachment #1: Type: text/plain, Size: 3657 bytes --]

David Miller a écrit :
> From: Andi Kleen <ak@suse.de>
> Date: Sun, 4 Nov 2007 00:18:14 +0100
> 
>> On Thursday 01 November 2007 11:16:20 Eric Dumazet wrote:
>>
>> Some quick comments:
>>
>>> +#if defined(CONFIG_SMP) || defined(CONFIG_PROVE_LOCKING)
>>> +/*
>>> + * Instead of using one rwlock for each inet_ehash_bucket, we use a table of locks
>>> + * The size of this table is a power of two and depends on the number of CPUS.
>>> + */
>> This shouldn't be hard coded based on NR_CPUS, but be done on runtime
>> based on num_possible_cpus(). This is better for kernels with a large
>> NR_CPUS, but which typically run on much smaller systems (like 
>> distribution kernels) 
> 
> I think this is a good idea.  Eric, could you make this change?

Yes of course, since using a non constant value for masking is cheap.

But I suspect distributions kernels enable CONFIG_HOTPLUG_CPU so 
num_possible_cpus() will be NR_CPUS.

> 
>> Also the EHASH_LOCK_SZ == 0 special case is a little strange. Why did
>> you add that?
> 
> He explained this in another reply, because ifdefs are ugly.

This will vanish if done on runtime anyway.

> 
>> And as a unrelated node have you tried converting the rwlocks 
>> into normal spinlocks? spinlocks should be somewhat cheaper
>> because they have less cache protocol overhead and with
>> the huge thash tables in Linux the chain walks should be short
>> anyways so not doing this in parallel is probably not a big issue.
>> At some point I also had a crazy idea of using a special locking
>> scheme that special cases the common case that a hash chain
>> has only one member and doesn't take a look for that at all. 
> 
> I agree.
> 
> There was movement at one point to get rid of all rwlock's in the
> kernel, I personally think they are pointless.  Any use that makes
> "sense" is a case where the code should be rewritten to decrease the
> lock hold time or convert to RCU.
> 

I agree too, rwlocks are more expensive when contention is low, so let do this 
rwlock->spinlock change on next step (separate patch), because it means 
changing also lhash_lock.

Thanks to Jarek, I added locks cleanup in dccp_fini()

[PATCH] INET : removes per bucket rwlock in tcp/dccp ehash table

As done two years ago on IP route cache table (commit 
22c047ccbc68fa8f3fa57f0e8f906479a062c426) , we can avoid using one lock per 
hash bucket for the huge TCP/DCCP hash tables.

On a typical x86_64 platform, this saves about 2MB or 4MB of ram, for litle 
performance differences. (we hit a different cache line for the rwlock, but 
then the bucket cache line have a better sharing factor among cpus, since we 
dirty it less often). For netstat or ss commands that want a full scan of hash 
table, we perform fewer memory accesses.

Using a 'small' table of hashed rwlocks should be more than enough to provide 
correct SMP concurrency between different buckets, without using too much 
memory. Sizing of this table depends on num_possible_cpus() and various CONFIG 
settings.

This patch provides some locking abstraction that may ease a future work using 
  a different model for TCP/DCCP table.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>

  include/net/inet_hashtables.h |   71 +++++++++++++++++++++++++++++---
  net/dccp/proto.c              |    9 +++-
  net/ipv4/inet_diag.c          |    9 ++--
  net/ipv4/inet_hashtables.c    |    7 +--
  net/ipv4/inet_timewait_sock.c |   13 +++--
  net/ipv4/tcp.c                |    4 -
  net/ipv4/tcp_ipv4.c           |   11 ++--
  net/ipv6/inet6_hashtables.c   |   19 ++++----
  8 files changed, 106 insertions(+), 37 deletions(-)


[-- Attachment #2: tcp_ehash_locks.patch --]
[-- Type: text/plain, Size: 14142 bytes --]

diff --git a/include/net/inet_hashtables.h b/include/net/inet_hashtables.h
index 4427dcd..8461cda 100644
--- a/include/net/inet_hashtables.h
+++ b/include/net/inet_hashtables.h
@@ -37,7 +37,6 @@
  * I'll experiment with dynamic table growth later.
  */
 struct inet_ehash_bucket {
-	rwlock_t	  lock;
 	struct hlist_head chain;
 	struct hlist_head twchain;
 };
@@ -100,6 +99,9 @@ struct inet_hashinfo {
 	 * TIME_WAIT sockets use a separate chain (twchain).
 	 */
 	struct inet_ehash_bucket	*ehash;
+	rwlock_t			*ehash_locks;
+	unsigned int			ehash_size;
+	unsigned int			ehash_locks_mask;
 
 	/* Ok, let's try this, I give up, we do need a local binding
 	 * TCP hash as well as the others for fast bind/connect.
@@ -107,7 +109,7 @@ struct inet_hashinfo {
 	struct inet_bind_hashbucket	*bhash;
 
 	unsigned int			bhash_size;
-	unsigned int			ehash_size;
+	/* Note : 4 bytes padding on 64 bit arches */
 
 	/* All sockets in TCP_LISTEN state will be in here.  This is the only
 	 * table where wildcard'd TCP sockets can exist.  Hash function here
@@ -134,6 +136,62 @@ static inline struct inet_ehash_bucket *inet_ehash_bucket(
 	return &hashinfo->ehash[hash & (hashinfo->ehash_size - 1)];
 }
 
+static inline rwlock_t *inet_ehash_lockp(
+	struct inet_hashinfo *hashinfo,
+	unsigned int hash)
+{
+	return &hashinfo->ehash_locks[hash & hashinfo->ehash_locks_mask];
+}
+
+static inline int inet_ehash_locks_alloc(struct inet_hashinfo *hashinfo)
+{
+	unsigned int i, size = 256;
+#if defined(CONFIG_PROVE_LOCKING)
+	unsigned int nr_pcpus = 2;
+#else
+	unsigned int nr_pcpus = num_possible_cpus();
+#endif
+	if (nr_pcpus >= 4)
+		size = 512;
+	if (nr_pcpus >= 8)
+		size = 1024;
+	if (nr_pcpus >= 16)
+		size = 2048;
+	if (nr_pcpus >= 32)
+		size = 4096;
+	if (sizeof(rwlock_t) != 0) {
+#ifdef CONFIG_NUMA
+		if (size * sizeof(rwlock_t) > PAGE_SIZE)
+			hashinfo->ehash_locks = vmalloc(size * sizeof(rwlock_t));
+		else
+#endif
+		hashinfo->ehash_locks =	kmalloc(size * sizeof(rwlock_t),
+						GFP_KERNEL);
+		if (!hashinfo->ehash_locks)
+			return ENOMEM;
+		for (i = 0; i < size; i++)
+			rwlock_init(&hashinfo->ehash_locks[i]);
+	}
+	hashinfo->ehash_locks_mask = size - 1;
+	return 0;
+}
+
+static inline void inet_ehash_locks_free(struct inet_hashinfo *hashinfo)
+{
+	if (hashinfo->ehash_locks) {
+#ifdef CONFIG_NUMA
+		unsigned int size = (hashinfo->ehash_locks_mask + 1) *
+							sizeof(rwlock_t);
+		if (size > PAGE_SIZE)
+			vfree(hashinfo->ehash_locks);
+		else
+#else
+		kfree(hashinfo->ehash_locks);
+#endif
+		hashinfo->ehash_locks = NULL;
+	}
+}
+
 extern struct inet_bind_bucket *
 		    inet_bind_bucket_create(struct kmem_cache *cachep,
 					    struct inet_bind_hashbucket *head,
@@ -222,7 +280,7 @@ static inline void __inet_hash(struct inet_hashinfo *hashinfo,
 		sk->sk_hash = inet_sk_ehashfn(sk);
 		head = inet_ehash_bucket(hashinfo, sk->sk_hash);
 		list = &head->chain;
-		lock = &head->lock;
+		lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 		write_lock(lock);
 	}
 	__sk_add_node(sk, list);
@@ -253,7 +311,7 @@ static inline void inet_unhash(struct inet_hashinfo *hashinfo, struct sock *sk)
 		inet_listen_wlock(hashinfo);
 		lock = &hashinfo->lhash_lock;
 	} else {
-		lock = &inet_ehash_bucket(hashinfo, sk->sk_hash)->lock;
+		lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 		write_lock_bh(lock);
 	}
 
@@ -354,9 +412,10 @@ static inline struct sock *
 	 */
 	unsigned int hash = inet_ehashfn(daddr, hnum, saddr, sport);
 	struct inet_ehash_bucket *head = inet_ehash_bucket(hashinfo, hash);
+	rwlock_t *lock = inet_ehash_lockp(hashinfo, hash);
 
 	prefetch(head->chain.first);
-	read_lock(&head->lock);
+	read_lock(lock);
 	sk_for_each(sk, node, &head->chain) {
 		if (INET_MATCH(sk, hash, acookie, saddr, daddr, ports, dif))
 			goto hit; /* You sunk my battleship! */
@@ -369,7 +428,7 @@ static inline struct sock *
 	}
 	sk = NULL;
 out:
-	read_unlock(&head->lock);
+	read_unlock(lock);
 	return sk;
 hit:
 	sock_hold(sk);
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index d849739..7a3bea9 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -1072,11 +1072,13 @@ static int __init dccp_init(void)
 	}
 
 	for (i = 0; i < dccp_hashinfo.ehash_size; i++) {
-		rwlock_init(&dccp_hashinfo.ehash[i].lock);
 		INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].chain);
 		INIT_HLIST_HEAD(&dccp_hashinfo.ehash[i].twchain);
 	}
 
+	if (inet_ehash_locks_alloc(&dccp_hashinfo))
+			goto out_free_dccp_ehash;
+
 	bhash_order = ehash_order;
 
 	do {
@@ -1091,7 +1093,7 @@ static int __init dccp_init(void)
 
 	if (!dccp_hashinfo.bhash) {
 		DCCP_CRIT("Failed to allocate DCCP bind hash table");
-		goto out_free_dccp_ehash;
+		goto out_free_dccp_locks;
 	}
 
 	for (i = 0; i < dccp_hashinfo.bhash_size; i++) {
@@ -1121,6 +1123,8 @@ out_free_dccp_mib:
 out_free_dccp_bhash:
 	free_pages((unsigned long)dccp_hashinfo.bhash, bhash_order);
 	dccp_hashinfo.bhash = NULL;
+out_free_dccp_locks:
+	inet_ehash_locks_free(&dccp_hashinfo);
 out_free_dccp_ehash:
 	free_pages((unsigned long)dccp_hashinfo.ehash, ehash_order);
 	dccp_hashinfo.ehash = NULL;
@@ -1139,6 +1143,7 @@ static void __exit dccp_fini(void)
 	free_pages((unsigned long)dccp_hashinfo.ehash,
 		   get_order(dccp_hashinfo.ehash_size *
 			     sizeof(struct inet_ehash_bucket)));
+	inet_ehash_locks_free(&dccp_hashinfo);
 	kmem_cache_destroy(dccp_hashinfo.bind_bucket_cachep);
 	dccp_ackvec_exit();
 	dccp_sysctl_exit();
diff --git a/net/ipv4/inet_diag.c b/net/ipv4/inet_diag.c
index dc429b6..b017073 100644
--- a/net/ipv4/inet_diag.c
+++ b/net/ipv4/inet_diag.c
@@ -747,13 +747,14 @@ skip_listen_ht:
 
 	for (i = s_i; i < hashinfo->ehash_size; i++) {
 		struct inet_ehash_bucket *head = &hashinfo->ehash[i];
+		rwlock_t *lock = inet_ehash_lockp(hashinfo, i);
 		struct sock *sk;
 		struct hlist_node *node;
 
 		if (i > s_i)
 			s_num = 0;
 
-		read_lock_bh(&head->lock);
+		read_lock_bh(lock);
 		num = 0;
 		sk_for_each(sk, node, &head->chain) {
 			struct inet_sock *inet = inet_sk(sk);
@@ -769,7 +770,7 @@ skip_listen_ht:
 			    r->id.idiag_dport)
 				goto next_normal;
 			if (inet_csk_diag_dump(sk, skb, cb) < 0) {
-				read_unlock_bh(&head->lock);
+				read_unlock_bh(lock);
 				goto done;
 			}
 next_normal:
@@ -791,14 +792,14 @@ next_normal:
 				    r->id.idiag_dport)
 					goto next_dying;
 				if (inet_twsk_diag_dump(tw, skb, cb) < 0) {
-					read_unlock_bh(&head->lock);
+					read_unlock_bh(lock);
 					goto done;
 				}
 next_dying:
 				++num;
 			}
 		}
-		read_unlock_bh(&head->lock);
+		read_unlock_bh(lock);
 	}
 
 done:
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 16eecc7..67704da 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -204,12 +204,13 @@ static int __inet_check_established(struct inet_timewait_death_row *death_row,
 	const __portpair ports = INET_COMBINED_PORTS(inet->dport, lport);
 	unsigned int hash = inet_ehashfn(daddr, lport, saddr, inet->dport);
 	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
+	rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
 	struct sock *sk2;
 	const struct hlist_node *node;
 	struct inet_timewait_sock *tw;
 
 	prefetch(head->chain.first);
-	write_lock(&head->lock);
+	write_lock(lock);
 
 	/* Check TIME-WAIT sockets first. */
 	sk_for_each(sk2, node, &head->twchain) {
@@ -239,7 +240,7 @@ unique:
 	BUG_TRAP(sk_unhashed(sk));
 	__sk_add_node(sk, &head->chain);
 	sock_prot_inc_use(sk->sk_prot);
-	write_unlock(&head->lock);
+	write_unlock(lock);
 
 	if (twp) {
 		*twp = tw;
@@ -255,7 +256,7 @@ unique:
 	return 0;
 
 not_unique:
-	write_unlock(&head->lock);
+	write_unlock(lock);
 	return -EADDRNOTAVAIL;
 }
 
diff --git a/net/ipv4/inet_timewait_sock.c b/net/ipv4/inet_timewait_sock.c
index 4e189e2..a60b99e 100644
--- a/net/ipv4/inet_timewait_sock.c
+++ b/net/ipv4/inet_timewait_sock.c
@@ -20,16 +20,16 @@ static void __inet_twsk_kill(struct inet_timewait_sock *tw,
 	struct inet_bind_hashbucket *bhead;
 	struct inet_bind_bucket *tb;
 	/* Unlink from established hashes. */
-	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, tw->tw_hash);
+	rwlock_t *lock = inet_ehash_lockp(hashinfo, tw->tw_hash);
 
-	write_lock(&ehead->lock);
+	write_lock(lock);
 	if (hlist_unhashed(&tw->tw_node)) {
-		write_unlock(&ehead->lock);
+		write_unlock(lock);
 		return;
 	}
 	__hlist_del(&tw->tw_node);
 	sk_node_init(&tw->tw_node);
-	write_unlock(&ehead->lock);
+	write_unlock(lock);
 
 	/* Disassociate with bind bucket. */
 	bhead = &hashinfo->bhash[inet_bhashfn(tw->tw_num, hashinfo->bhash_size)];
@@ -59,6 +59,7 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
 	const struct inet_sock *inet = inet_sk(sk);
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 	struct inet_ehash_bucket *ehead = inet_ehash_bucket(hashinfo, sk->sk_hash);
+	rwlock_t *lock = inet_ehash_lockp(hashinfo, sk->sk_hash);
 	struct inet_bind_hashbucket *bhead;
 	/* Step 1: Put TW into bind hash. Original socket stays there too.
 	   Note, that any socket with inet->num != 0 MUST be bound in
@@ -71,7 +72,7 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
 	inet_twsk_add_bind_node(tw, &tw->tw_tb->owners);
 	spin_unlock(&bhead->lock);
 
-	write_lock(&ehead->lock);
+	write_lock(lock);
 
 	/* Step 2: Remove SK from established hash. */
 	if (__sk_del_node_init(sk))
@@ -81,7 +82,7 @@ void __inet_twsk_hashdance(struct inet_timewait_sock *tw, struct sock *sk,
 	inet_twsk_add_node(tw, &ehead->twchain);
 	atomic_inc(&tw->tw_refcnt);
 
-	write_unlock(&ehead->lock);
+	write_unlock(lock);
 }
 
 EXPORT_SYMBOL_GPL(__inet_twsk_hashdance);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index c64072b..8e65182 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2456,11 +2456,11 @@ void __init tcp_init(void)
 					thash_entries ? 0 : 512 * 1024);
 	tcp_hashinfo.ehash_size = 1 << tcp_hashinfo.ehash_size;
 	for (i = 0; i < tcp_hashinfo.ehash_size; i++) {
-		rwlock_init(&tcp_hashinfo.ehash[i].lock);
 		INIT_HLIST_HEAD(&tcp_hashinfo.ehash[i].chain);
 		INIT_HLIST_HEAD(&tcp_hashinfo.ehash[i].twchain);
 	}
-
+	if (inet_ehash_locks_alloc(&tcp_hashinfo))
+		panic("TCP: failed to alloc ehash_locks");
 	tcp_hashinfo.bhash =
 		alloc_large_system_hash("TCP bind",
 					sizeof(struct inet_bind_hashbucket),
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index eec02b2..cd82c0e 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -2049,8 +2049,9 @@ static void *established_get_first(struct seq_file *seq)
 		struct sock *sk;
 		struct hlist_node *node;
 		struct inet_timewait_sock *tw;
+		rwlock_t *lock = inet_ehash_lockp(&tcp_hashinfo, st->bucket);
 
-		read_lock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+		read_lock_bh(lock);
 		sk_for_each(sk, node, &tcp_hashinfo.ehash[st->bucket].chain) {
 			if (sk->sk_family != st->family) {
 				continue;
@@ -2067,7 +2068,7 @@ static void *established_get_first(struct seq_file *seq)
 			rc = tw;
 			goto out;
 		}
-		read_unlock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+		read_unlock_bh(lock);
 		st->state = TCP_SEQ_STATE_ESTABLISHED;
 	}
 out:
@@ -2094,11 +2095,11 @@ get_tw:
 			cur = tw;
 			goto out;
 		}
-		read_unlock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+		read_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
 		st->state = TCP_SEQ_STATE_ESTABLISHED;
 
 		if (++st->bucket < tcp_hashinfo.ehash_size) {
-			read_lock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+			read_lock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
 			sk = sk_head(&tcp_hashinfo.ehash[st->bucket].chain);
 		} else {
 			cur = NULL;
@@ -2206,7 +2207,7 @@ static void tcp_seq_stop(struct seq_file *seq, void *v)
 	case TCP_SEQ_STATE_TIME_WAIT:
 	case TCP_SEQ_STATE_ESTABLISHED:
 		if (v)
-			read_unlock_bh(&tcp_hashinfo.ehash[st->bucket].lock);
+			read_unlock_bh(inet_ehash_lockp(&tcp_hashinfo, st->bucket));
 		break;
 	}
 }
diff --git a/net/ipv6/inet6_hashtables.c b/net/ipv6/inet6_hashtables.c
index d6f1026..adc73ad 100644
--- a/net/ipv6/inet6_hashtables.c
+++ b/net/ipv6/inet6_hashtables.c
@@ -37,9 +37,8 @@ void __inet6_hash(struct inet_hashinfo *hashinfo,
 	} else {
 		unsigned int hash;
 		sk->sk_hash = hash = inet6_sk_ehashfn(sk);
-		hash &= (hashinfo->ehash_size - 1);
-		list = &hashinfo->ehash[hash].chain;
-		lock = &hashinfo->ehash[hash].lock;
+		list = &inet_ehash_bucket(hashinfo, hash)->chain;
+		lock = inet_ehash_lockp(hashinfo, hash);
 		write_lock(lock);
 	}
 
@@ -70,9 +69,10 @@ struct sock *__inet6_lookup_established(struct inet_hashinfo *hashinfo,
 	 */
 	unsigned int hash = inet6_ehashfn(daddr, hnum, saddr, sport);
 	struct inet_ehash_bucket *head = inet_ehash_bucket(hashinfo, hash);
+	rwlock_t *lock = inet_ehash_lockp(hashinfo, hash);
 
 	prefetch(head->chain.first);
-	read_lock(&head->lock);
+	read_lock(lock);
 	sk_for_each(sk, node, &head->chain) {
 		/* For IPV6 do the cheaper port and family tests first. */
 		if (INET6_MATCH(sk, hash, saddr, daddr, ports, dif))
@@ -92,12 +92,12 @@ struct sock *__inet6_lookup_established(struct inet_hashinfo *hashinfo,
 				goto hit;
 		}
 	}
-	read_unlock(&head->lock);
+	read_unlock(lock);
 	return NULL;
 
 hit:
 	sock_hold(sk);
-	read_unlock(&head->lock);
+	read_unlock(lock);
 	return sk;
 }
 EXPORT_SYMBOL(__inet6_lookup_established);
@@ -175,12 +175,13 @@ static int __inet6_check_established(struct inet_timewait_death_row *death_row,
 	const unsigned int hash = inet6_ehashfn(daddr, lport, saddr,
 						inet->dport);
 	struct inet_ehash_bucket *head = inet_ehash_bucket(hinfo, hash);
+	rwlock_t *lock = inet_ehash_lockp(hinfo, hash);
 	struct sock *sk2;
 	const struct hlist_node *node;
 	struct inet_timewait_sock *tw;
 
 	prefetch(head->chain.first);
-	write_lock(&head->lock);
+	write_lock(lock);
 
 	/* Check TIME-WAIT sockets first. */
 	sk_for_each(sk2, node, &head->twchain) {
@@ -216,7 +217,7 @@ unique:
 	__sk_add_node(sk, &head->chain);
 	sk->sk_hash = hash;
 	sock_prot_inc_use(sk->sk_prot);
-	write_unlock(&head->lock);
+	write_unlock(lock);
 
 	if (twp != NULL) {
 		*twp = tw;
@@ -231,7 +232,7 @@ unique:
 	return 0;
 
 not_unique:
-	write_unlock(&head->lock);
+	write_unlock(lock);
 	return -EADDRNOTAVAIL;
 }