When adding rb-tree for TCP retransmit queue, we inadvertently broke
TCP autocorking.
tcp_should_autocork() should really check if the rtx queue is not empty.
Tested:
Before the fix :
$ nstat -n;./netperf -H 10.246.7.152 -Cc -- -m 500;nstat | grep AutoCork
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.7.152
() port 0 AF_INET
Recv Send Send Utilization Service Demand
Socket Socket Message Elapsed Send Recv Send Recv
Size Size Size Time Throughput local remote local remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
540000 262144 500 10.00 2682.85 2.47 1.59 3.618 2.329
TcpExtTCPAutoCorking 33 0.0
// Same test, but forcing TCP_NODELAY
$ nstat -n;./netperf -H 10.246.7.152 -Cc -- -D -m 500;nstat | grep AutoCork
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.7.152
() port 0 AF_INET : nodelay
Recv Send Send Utilization Service Demand
Socket Socket Message Elapsed Send Recv Send Recv
Size Size Size Time Throughput local remote local remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
540000 262144 500 10.00 1408.75 2.44 2.96 6.802 8.259
TcpExtTCPAutoCorking 1 0.0
After the fix :
$ nstat -n;./netperf -H 10.246.7.152 -Cc -- -m 500;nstat | grep AutoCork
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.7.152
() port 0 AF_INET
Recv Send Send Utilization Service Demand
Socket Socket Message Elapsed Send Recv Send Recv
Size Size Size Time Throughput local remote local remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
540000 262144 500 10.00 5472.46 2.45 1.43 1.761 1.027
TcpExtTCPAutoCorking 361293 0.0
// With TCP_NODELAY option
$ nstat -n;./netperf -H 10.246.7.152 -Cc -- -D -m 500;nstat | grep AutoCork
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.246.7.152
() port 0 AF_INET : nodelay
Recv Send Send Utilization Service Demand
Socket Socket Message Elapsed Send Recv Send Recv
Size Size Size Time Throughput local remote local remote
bytes bytes bytes secs. 10^6bits/s % S % S us/KB us/KB
540000 262144 500 10.00 5454.96 2.46 1.63 1.775 1.174
TcpExtTCPAutoCorking 315448 0.0
Fixes: 75c119afe14f ("tcp: implement rb-tree based retransmit queue")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Reported-by: Michael Wenig <mwe...@vmware.com>
Tested-by: Michael Wenig <mwe...@vmware.com>
---
net/ipv4/tcp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index
44be7f43455e4aefde8db61e2d941a69abcc642a..c9d00ef54deca15d5760bcbe154001a96fa1e2a7
100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -697,7 +697,7 @@ static bool tcp_should_autocork(struct sock *sk, struct
sk_buff *skb,
{
return skb->len < size_goal &&
sock_net(sk)->ipv4.sysctl_tcp_autocorking &&
- skb != tcp_write_queue_head(sk) &&
+ !tcp_rtx_queue_empty(sk) &&
refcount_read(&sk->sk_wmem_alloc) > skb->truesize;
}
--
2.17.0.441.gb46fe60e1d-goog
