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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

4
net/ipv6/tcp_ipv6.c
View File

@@ -1486,7 +1486,7 @@ do_time_wait:
ntohs(th->dest), tcp_v6_iif(skb));
if (sk2) {
struct inet_timewait_sock *tw = inet_twsk(sk);
inet_twsk_deschedule(tw, &tcp_death_row);
inet_twsk_deschedule(tw);
inet_twsk_put(tw);
sk = sk2;
tcp_v6_restore_cb(skb);
@@ -1728,9 +1728,9 @@ static void get_tcp6_sock(struct seq_file *seq, struct sock *sp, int i)
static void get_timewait6_sock(struct seq_file *seq,
struct inet_timewait_sock *tw, int i)
{
long delta = tw->tw_timer.expires - jiffies;
const struct in6_addr *dest, *src;
__u16 destp, srcp;
s32 delta = tw->tw_ttd - inet_tw_time_stamp();
dest = &tw->tw_v6_daddr;
src = &tw->tw_v6_rcv_saddr;