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Date: Tue, 29 Jul 2014 17:34:20 +0100
From: Thomas Graf <tgraf@...g.ch>
To: Tobias Klauser <tklauser@...tanz.ch>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org, kaber@...sh.net,
paulmck@...ux.vnet.ibm.com, josh@...htriplett.org,
challa@...ronetworks.com, walpole@...pdx.edu, dev@...nvswitch.org
Subject: Re: [PATCH 2/2] netlink: Convert netlink_lookup() to use RCU
protected hash table
On 07/29/14 at 05:58pm, Tobias Klauser wrote:
> On 2014-07-29 at 13:41:33 +0200, Thomas Graf <tgraf@...g.ch> wrote:
> > Heavy Netlink users such as Open vSwitch spend a considerable amount of
> > time in netlink_lookup() due to the read-lock on nl_table_lock. Use of
> > RCU relieves the lock contention.
> >
> > Makes use of the new resizable hash table to avoid locking on the
> > lookup.
> >
> > The hash table will grow if entries exceeds 75% of table size up to a
> > total table size of 64K. It will automatically shrink if usage falls
> > below 50%.
> >
> > Also splits nl_table_lock into a separate spinlock to protect hash table
> > mutations. This avoids a possible deadlock when the hash table growing
> > waits on RCU readers to complete via synchronize_rcu() while readers
> > holding RCU read lock are waiting on the nl_table_lock() to be released
> > to lock the table for broadcasting.
> >
> > Before:
> > 9.16% kpktgend_0 [openvswitch] [k] masked_flow_lookup
> > 6.42% kpktgend_0 [pktgen] [k] mod_cur_headers
> > 6.26% kpktgend_0 [pktgen] [k] pktgen_thread_worker
> > 6.23% kpktgend_0 [kernel.kallsyms] [k] memset
> > 4.79% kpktgend_0 [kernel.kallsyms] [k] netlink_lookup
> > 4.37% kpktgend_0 [kernel.kallsyms] [k] memcpy
> > 3.60% kpktgend_0 [openvswitch] [k] ovs_flow_extract
> > 2.69% kpktgend_0 [kernel.kallsyms] [k] jhash2
> >
> > After:
> > 15.26% kpktgend_0 [openvswitch] [k] masked_flow_lookup
> > 8.12% kpktgend_0 [pktgen] [k] pktgen_thread_worker
> > 7.92% kpktgend_0 [pktgen] [k] mod_cur_headers
> > 5.11% kpktgend_0 [kernel.kallsyms] [k] memset
> > 4.11% kpktgend_0 [openvswitch] [k] ovs_flow_extract
> > 4.06% kpktgend_0 [kernel.kallsyms] [k] _raw_spin_lock
> > 3.90% kpktgend_0 [kernel.kallsyms] [k] jhash2
> > [...]
> > 0.67% kpktgend_0 [kernel.kallsyms] [k] netlink_lookup
> >
> > Signed-off-by: Thomas Graf <tgraf@...g.ch>
> > ---
> > net/netlink/af_netlink.c | 285 ++++++++++++++++++-----------------------------
> > net/netlink/af_netlink.h | 18 +--
> > net/netlink/diag.c | 11 +-
> > 3 files changed, 119 insertions(+), 195 deletions(-)
> >
> > diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> > index 1b38f7f..7f44468 100644
> > --- a/net/netlink/af_netlink.c
> > +++ b/net/netlink/af_netlink.c
> [...]
> > @@ -2996,28 +2939,26 @@ static void *netlink_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> >
> > net = seq_file_net(seq);
> > iter = seq->private;
> > - s = v;
> > - do {
> > - s = sk_next(s);
> > - } while (s && !nl_table[s->sk_protocol].compare(net, s));
> > - if (s)
> > - return s;
> > + nlk = v;
> > +
> > + rht_for_each_entry_rcu(nlk, nlk->node.next, node)
> > + if (net_eq(sock_net((struct sock *)nlk), net))
> > + return nlk;
> >
> > i = iter->link;
> > j = iter->hash_idx + 1;
> >
> > do {
> > - struct nl_portid_hash *hash = &nl_table[i].hash;
> > -
> > - for (; j <= hash->mask; j++) {
> > - s = sk_head(&hash->table[j]);
> > + struct rhashtable *ht = &nl_table[i].hash;
> > + const struct bucket_table *tbl = rht_dereference(ht->tbl, ht);
> >
> > - while (s && !nl_table[s->sk_protocol].compare(net, s))
> > - s = sk_next(s);
> > - if (s) {
> > - iter->link = i;
> > - iter->hash_idx = j;
> > - return s;
> > + for (; j <= tbl->size; j++) {
>
> Should the condition j < tbl->size here, since the bucket table only
> contains `size' buckets?
Good catch, thanks
>
>
> > + rht_for_each_entry_rcu(nlk, tbl->buckets[j], node) {
> > + if (net_eq(sock_net((struct sock *)nlk), net)) {
> > + iter->link = i;
> > + iter->hash_idx = j;
> > + return nlk;
> > + }
> > }
> > }
> [...]
> > diff --git a/net/netlink/diag.c b/net/netlink/diag.c
> > index 1af29624..7588f34 100644
> > --- a/net/netlink/diag.c
> > +++ b/net/netlink/diag.c
> [...]
> > @@ -101,16 +102,20 @@ static int __netlink_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
> > int protocol, int s_num)
> > {
> > struct netlink_table *tbl = &nl_table[protocol];
> > - struct nl_portid_hash *hash = &tbl->hash;
> > + struct rhashtable *ht = &tbl->hash;
> > + const struct bucket_table *htbl = rht_dereference(ht->tbl, ht);
> > struct net *net = sock_net(skb->sk);
> > struct netlink_diag_req *req;
> > + struct netlink_sock *nlsk;
> > struct sock *sk;
> > int ret = 0, num = 0, i;
> >
> > req = nlmsg_data(cb->nlh);
> >
> > - for (i = 0; i <= hash->mask; i++) {
> > - sk_for_each(sk, &hash->table[i]) {
> > + for (i = 0; i <= htbl->size; i++) {
>
> Same here, condition should be i < htbl->size
>
> > + rht_for_each_entry(nlsk, htbl->buckets[i], ht, node) {
> > + sk = (struct sock *)nlsk;
> > +
> > if (!net_eq(sock_net(sk), net))
> > continue;
> > if (num < s_num) {
> > --
> > 1.9.3
>
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