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| author | Eric Dumazet <edumazet@google.com> | 2015-10-02 11:43:35 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2015-10-03 04:32:43 -0700 |
| commit | ca6fb06518836ef9b65dc0aac02ff97704d52a05 (patch) | |
| tree | 3fbe433aac9dcf1cae49e6715ced18bd3505d811 /net/sched | |
| parent | 1b33bc3e9e903f7293f7dfe80a875b2a5d0305aa (diff) | |
| download | lwn-ca6fb06518836ef9b65dc0aac02ff97704d52a05.tar.gz lwn-ca6fb06518836ef9b65dc0aac02ff97704d52a05.zip | |
tcp: attach SYNACK messages to request sockets instead of listener
If a listen backlog is very big (to avoid syncookies), then
the listener sk->sk_wmem_alloc is the main source of false
sharing, as we need to touch it twice per SYNACK re-transmit
and TX completion.
(One SYN packet takes listener lock once, but up to 6 SYNACK
are generated)
By attaching the skb to the request socket, we remove this
source of contention.
Tested:
listen(fd, 10485760); // single listener (no SO_REUSEPORT)
16 RX/TX queue NIC
Sustain a SYNFLOOD attack of ~320,000 SYN per second,
Sending ~1,400,000 SYNACK per second.
Perf profiles now show listener spinlock being next bottleneck.
20.29% [kernel] [k] queued_spin_lock_slowpath
10.06% [kernel] [k] __inet_lookup_established
5.12% [kernel] [k] reqsk_timer_handler
3.22% [kernel] [k] get_next_timer_interrupt
3.00% [kernel] [k] tcp_make_synack
2.77% [kernel] [k] ipt_do_table
2.70% [kernel] [k] run_timer_softirq
2.50% [kernel] [k] ip_finish_output
2.04% [kernel] [k] cascade
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/sched')
| -rw-r--r-- | net/sched/sch_fq.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/net/sched/sch_fq.c b/net/sched/sch_fq.c index f377702d4b91..3386cce4751e 100644 --- a/net/sched/sch_fq.c +++ b/net/sched/sch_fq.c @@ -224,13 +224,15 @@ static struct fq_flow *fq_classify(struct sk_buff *skb, struct fq_sched_data *q) if (unlikely((skb->priority & TC_PRIO_MAX) == TC_PRIO_CONTROL)) return &q->internal; - /* SYNACK messages are attached to a listener socket. - * 1) They are not part of a 'flow' yet - * 2) We do not want to rate limit them (eg SYNFLOOD attack), + /* SYNACK messages are attached to a TCP_NEW_SYN_RECV request socket + * 1) request sockets are not full blown, + * they do not contain sk_pacing_rate + * 2) They are not part of a 'flow' yet + * 3) We do not want to rate limit them (eg SYNFLOOD attack), * especially if the listener set SO_MAX_PACING_RATE - * 3) We pretend they are orphaned + * 4) We pretend they are orphaned */ - if (!sk || sk->sk_state == TCP_LISTEN) { + if (!sk || sk->sk_state == TCP_NEW_SYN_RECV) { unsigned long hash = skb_get_hash(skb) & q->orphan_mask; /* By forcing low order bit to 1, we make sure to not |