From a8b690f98baf9fb1902b8eeab801351ea603fa3a Mon Sep 17 00:00:00 2001 From: Tom Herbert Date: Mon, 7 Jun 2010 00:43:42 -0700 Subject: [PATCH] tcp: Fix slowness in read /proc/net/tcp This patch address a serious performance issue in reading the TCP sockets table (/proc/net/tcp). Reading the full table is done by a number of sequential read operations. At each read operation, a seek is done to find the last socket that was previously read. This seek operation requires that the sockets in the table need to be counted up to the current file position, and to count each of these requires taking a lock for each non-empty bucket. The whole algorithm is O(n^2). The fix is to cache the last bucket value, offset within the bucket, and the file position returned by the last read operation. On the next sequential read, the bucket and offset are used to find the last read socket immediately without needing ot scan the previous buckets the table. This algorithm t read the whole table is O(n). The improvement offered by this patch is easily show by performing cat'ing /proc/net/tcp on a machine with a lot of connections. With about 182K connections in the table, I see the following: - Without patch time cat /proc/net/tcp > /dev/null real 1m56.729s user 0m0.214s sys 1m56.344s - With patch time cat /proc/net/tcp > /dev/null real 0m0.894s user 0m0.290s sys 0m0.594s Signed-off-by: Tom Herbert Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- include/net/tcp.h | 3 +- net/ipv4/tcp_ipv4.c | 92 +++++++++++++++++++++++++++++++++++++++++---- 2 files changed, 86 insertions(+), 9 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index a1449144848a..573166484413 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1413,7 +1413,8 @@ struct tcp_iter_state { sa_family_t family; enum tcp_seq_states state; struct sock *syn_wait_sk; - int bucket, sbucket, num, uid; + int bucket, offset, sbucket, num, uid; + loff_t last_pos; }; extern int tcp_proc_register(struct net *net, struct tcp_seq_afinfo *afinfo); diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index acdc4c989853..7f976af27bf0 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1980,6 +1980,11 @@ static inline struct inet_timewait_sock *tw_next(struct inet_timewait_sock *tw) hlist_nulls_entry(tw->tw_node.next, typeof(*tw), tw_node) : NULL; } +/* + * Get next listener socket follow cur. If cur is NULL, get first socket + * starting from bucket given in st->bucket; when st->bucket is zero the + * very first socket in the hash table is returned. + */ static void *listening_get_next(struct seq_file *seq, void *cur) { struct inet_connection_sock *icsk; @@ -1990,14 +1995,15 @@ static void *listening_get_next(struct seq_file *seq, void *cur) struct net *net = seq_file_net(seq); if (!sk) { - st->bucket = 0; - ilb = &tcp_hashinfo.listening_hash[0]; + ilb = &tcp_hashinfo.listening_hash[st->bucket]; spin_lock_bh(&ilb->lock); sk = sk_nulls_head(&ilb->head); + st->offset = 0; goto get_sk; } ilb = &tcp_hashinfo.listening_hash[st->bucket]; ++st->num; + ++st->offset; if (st->state == TCP_SEQ_STATE_OPENREQ) { struct request_sock *req = cur; @@ -2012,6 +2018,7 @@ static void *listening_get_next(struct seq_file *seq, void *cur) } req = req->dl_next; } + st->offset = 0; if (++st->sbucket >= icsk->icsk_accept_queue.listen_opt->nr_table_entries) break; get_req: @@ -2047,6 +2054,7 @@ start_req: read_unlock_bh(&icsk->icsk_accept_queue.syn_wait_lock); } spin_unlock_bh(&ilb->lock); + st->offset = 0; if (++st->bucket < INET_LHTABLE_SIZE) { ilb = &tcp_hashinfo.listening_hash[st->bucket]; spin_lock_bh(&ilb->lock); @@ -2060,7 +2068,12 @@ out: static void *listening_get_idx(struct seq_file *seq, loff_t *pos) { - void *rc = listening_get_next(seq, NULL); + struct tcp_iter_state *st = seq->private; + void *rc; + + st->bucket = 0; + st->offset = 0; + rc = listening_get_next(seq, NULL); while (rc && *pos) { rc = listening_get_next(seq, rc); @@ -2075,13 +2088,18 @@ static inline int empty_bucket(struct tcp_iter_state *st) hlist_nulls_empty(&tcp_hashinfo.ehash[st->bucket].twchain); } +/* + * Get first established socket starting from bucket given in st->bucket. + * If st->bucket is zero, the very first socket in the hash is returned. + */ static void *established_get_first(struct seq_file *seq) { struct tcp_iter_state *st = seq->private; struct net *net = seq_file_net(seq); void *rc = NULL; - for (st->bucket = 0; st->bucket <= tcp_hashinfo.ehash_mask; ++st->bucket) { + st->offset = 0; + for (; st->bucket <= tcp_hashinfo.ehash_mask; ++st->bucket) { struct sock *sk; struct hlist_nulls_node *node; struct inet_timewait_sock *tw; @@ -2126,6 +2144,7 @@ static void *established_get_next(struct seq_file *seq, void *cur) struct net *net = seq_file_net(seq); ++st->num; + ++st->offset; if (st->state == TCP_SEQ_STATE_TIME_WAIT) { tw = cur; @@ -2142,6 +2161,7 @@ get_tw: st->state = TCP_SEQ_STATE_ESTABLISHED; /* Look for next non empty bucket */ + st->offset = 0; while (++st->bucket <= tcp_hashinfo.ehash_mask && empty_bucket(st)) ; @@ -2169,7 +2189,11 @@ out: static void *established_get_idx(struct seq_file *seq, loff_t pos) { - void *rc = established_get_first(seq); + struct tcp_iter_state *st = seq->private; + void *rc; + + st->bucket = 0; + rc = established_get_first(seq); while (rc && pos) { rc = established_get_next(seq, rc); @@ -2194,24 +2218,72 @@ static void *tcp_get_idx(struct seq_file *seq, loff_t pos) return rc; } +static void *tcp_seek_last_pos(struct seq_file *seq) +{ + struct tcp_iter_state *st = seq->private; + int offset = st->offset; + int orig_num = st->num; + void *rc = NULL; + + switch (st->state) { + case TCP_SEQ_STATE_OPENREQ: + case TCP_SEQ_STATE_LISTENING: + if (st->bucket >= INET_LHTABLE_SIZE) + break; + st->state = TCP_SEQ_STATE_LISTENING; + rc = listening_get_next(seq, NULL); + while (offset-- && rc) + rc = listening_get_next(seq, rc); + if (rc) + break; + st->bucket = 0; + /* Fallthrough */ + case TCP_SEQ_STATE_ESTABLISHED: + case TCP_SEQ_STATE_TIME_WAIT: + st->state = TCP_SEQ_STATE_ESTABLISHED; + if (st->bucket > tcp_hashinfo.ehash_mask) + break; + rc = established_get_first(seq); + while (offset-- && rc) + rc = established_get_next(seq, rc); + } + + st->num = orig_num; + + return rc; +} + static void *tcp_seq_start(struct seq_file *seq, loff_t *pos) { struct tcp_iter_state *st = seq->private; + void *rc; + + if (*pos && *pos == st->last_pos) { + rc = tcp_seek_last_pos(seq); + if (rc) + goto out; + } + st->state = TCP_SEQ_STATE_LISTENING; st->num = 0; - return *pos ? tcp_get_idx(seq, *pos - 1) : SEQ_START_TOKEN; + st->bucket = 0; + st->offset = 0; + rc = *pos ? tcp_get_idx(seq, *pos - 1) : SEQ_START_TOKEN; + +out: + st->last_pos = *pos; + return rc; } static void *tcp_seq_next(struct seq_file *seq, void *v, loff_t *pos) { + struct tcp_iter_state *st = seq->private; void *rc = NULL; - struct tcp_iter_state *st; if (v == SEQ_START_TOKEN) { rc = tcp_get_idx(seq, 0); goto out; } - st = seq->private; switch (st->state) { case TCP_SEQ_STATE_OPENREQ: @@ -2219,6 +2291,8 @@ static void *tcp_seq_next(struct seq_file *seq, void *v, loff_t *pos) rc = listening_get_next(seq, v); if (!rc) { st->state = TCP_SEQ_STATE_ESTABLISHED; + st->bucket = 0; + st->offset = 0; rc = established_get_first(seq); } break; @@ -2229,6 +2303,7 @@ static void *tcp_seq_next(struct seq_file *seq, void *v, loff_t *pos) } out: ++*pos; + st->last_pos = *pos; return rc; } @@ -2267,6 +2342,7 @@ static int tcp_seq_open(struct inode *inode, struct file *file) s = ((struct seq_file *)file->private_data)->private; s->family = afinfo->family; + s->last_pos = 0; return 0; }