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tcp/dccp: get rid of central timewait timer

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Using a timer wheel for timewait sockets was nice ~15 years ago when
memory was expensive and machines had a single processor.

This does not scale, code is ugly and source of huge latencies
(Typically 30 ms have been seen, cpus spinning on death_lock spinlock.)

We can afford to use an extra 64 bytes per timewait sock and spread
timewait load to all cpus to have better behavior.

Tested:

On following test, /proc/sys/net/ipv4/tcp_tw_recycle is set to 1
on the target (lpaa24)

Before patch :

lpaa23:~# ./super_netperf 200 -H lpaa24 -t TCP_CC -l 60 -- -p0,0
419594

lpaa23:~# ./super_netperf 200 -H lpaa24 -t TCP_CC -l 60 -- -p0,0
437171

While test is running, we can observe 25 or even 33 ms latencies.

lpaa24:~# ping -c 1000 -i 0.02 -qn lpaa23
...
1000 packets transmitted, 1000 received, 0% packet loss, time 20601ms
rtt min/avg/max/mdev = 0.020/0.217/25.771/1.535 ms, pipe 2

lpaa24:~# ping -c 1000 -i 0.02 -qn lpaa23
...
1000 packets transmitted, 1000 received, 0% packet loss, time 20702ms
rtt min/avg/max/mdev = 0.019/0.183/33.761/1.441 ms, pipe 2

After patch :

About 90% increase of throughput :

lpaa23:~# ./super_netperf 200 -H lpaa24 -t TCP_CC -l 60 -- -p0,0
810442

lpaa23:~# ./super_netperf 200 -H lpaa24 -t TCP_CC -l 60 -- -p0,0
800992

And latencies are kept to minimal values during this load, even
if network utilization is 90% higher :

lpaa24:~# ping -c 1000 -i 0.02 -qn lpaa23
...
1000 packets transmitted, 1000 received, 0% packet loss, time 19991ms
rtt min/avg/max/mdev = 0.023/0.064/0.360/0.042 ms

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2015-04-12 18:51:09 -07:00
committed by David S. Miller
parent 20a1d16526
commit 789f558cfb
11 changed files with 68 additions and 385 deletions
Download Patch File Download Diff File Expand all files Collapse all files

35
net/ipv4/tcp_minisocks.c
View File

@@ -34,18 +34,7 @@ int sysctl_tcp_abort_on_overflow __read_mostly;
struct inet_timewait_death_row tcp_death_row = {
.sysctl_max_tw_buckets = NR_FILE * 2,
.period = TCP_TIMEWAIT_LEN / INET_TWDR_TWKILL_SLOTS,
.death_lock = __SPIN_LOCK_UNLOCKED(tcp_death_row.death_lock),
.hashinfo = &tcp_hashinfo,
.tw_timer = TIMER_INITIALIZER(inet_twdr_hangman, 0,
(unsigned long)&tcp_death_row),
.twkill_work = __WORK_INITIALIZER(tcp_death_row.twkill_work,
inet_twdr_twkill_work),
/* Short-time timewait calendar */
.twcal_hand = -1,
.twcal_timer = TIMER_INITIALIZER(inet_twdr_twcal_tick, 0,
(unsigned long)&tcp_death_row),
};
EXPORT_SYMBOL_GPL(tcp_death_row);
@@ -158,7 +147,7 @@ tcp_timewait_state_process(struct inet_timewait_sock *tw, struct sk_buff *skb,
if (!th->fin ||
TCP_SKB_CB(skb)->end_seq != tcptw->tw_rcv_nxt + 1) {
kill_with_rst:
inet_twsk_deschedule(tw, &tcp_death_row);
inet_twsk_deschedule(tw);
inet_twsk_put(tw);
return TCP_TW_RST;
}
@@ -174,11 +163,9 @@ kill_with_rst:
if (tcp_death_row.sysctl_tw_recycle &&
tcptw->tw_ts_recent_stamp &&
tcp_tw_remember_stamp(tw))
inet_twsk_schedule(tw, &tcp_death_row, tw->tw_timeout,
TCP_TIMEWAIT_LEN);
inet_twsk_schedule(tw, tw->tw_timeout);
else
inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
TCP_TIMEWAIT_LEN);
inet_twsk_schedule(tw, TCP_TIMEWAIT_LEN);
return TCP_TW_ACK;
}
@@ -211,13 +198,12 @@ kill_with_rst:
*/
if (sysctl_tcp_rfc1337 == 0) {
kill:
inet_twsk_deschedule(tw, &tcp_death_row);
inet_twsk_deschedule(tw);
inet_twsk_put(tw);
return TCP_TW_SUCCESS;
}
}
inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
TCP_TIMEWAIT_LEN);
inet_twsk_schedule(tw, TCP_TIMEWAIT_LEN);
if (tmp_opt.saw_tstamp) {
tcptw->tw_ts_recent = tmp_opt.rcv_tsval;
@@ -267,8 +253,7 @@ kill:
* Do not reschedule in the last case.
*/
if (paws_reject || th->ack)
inet_twsk_schedule(tw, &tcp_death_row, TCP_TIMEWAIT_LEN,
TCP_TIMEWAIT_LEN);
inet_twsk_schedule(tw, TCP_TIMEWAIT_LEN);
return tcp_timewait_check_oow_rate_limit(
tw, skb, LINUX_MIB_TCPACKSKIPPEDTIMEWAIT);
@@ -283,16 +268,15 @@ EXPORT_SYMBOL(tcp_timewait_state_process);
*/
void tcp_time_wait(struct sock *sk, int state, int timeo)
{
struct inet_timewait_sock *tw = NULL;
const struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcp_sock *tp = tcp_sk(sk);
struct inet_timewait_sock *tw;
bool recycle_ok = false;
if (tcp_death_row.sysctl_tw_recycle && tp->rx_opt.ts_recent_stamp)
recycle_ok = tcp_remember_stamp(sk);
if (tcp_death_row.tw_count < tcp_death_row.sysctl_max_tw_buckets)
tw = inet_twsk_alloc(sk, state);
tw = inet_twsk_alloc(sk, &tcp_death_row, state);
if (tw) {
struct tcp_timewait_sock *tcptw = tcp_twsk((struct sock *)tw);
@@ -355,8 +339,7 @@ void tcp_time_wait(struct sock *sk, int state, int timeo)
timeo = TCP_TIMEWAIT_LEN;
}
inet_twsk_schedule(tw, &tcp_death_row, timeo,
TCP_TIMEWAIT_LEN);
inet_twsk_schedule(tw, timeo);
inet_twsk_put(tw);
} else {
/* Sorry, if we're out of memory, just CLOSE this