[PATCH net-next] tcp: minor optimization for calculating packets_out in tcp connect

[PATCH net-next] tcp: minor optimization for calculating packets_out in tcp connect

[Yafang Shao]

When we building a syn packet, the tcp_skb_pcount(skb) is always 1,
which is set in tcp_init_nondata_skb().
Regarding the syn_data, it is set through
memcpy(syn_data->cb, syn->cb, sizeof(syn->cb)),
which is always 1 as well.

So we don't need to use tcp_skb_pcount(skb), that could give us a
little improvement.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
 net/ipv4/tcp_output.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 730bc44..12bb5e7 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -3404,7 +3404,7 @@ static void tcp_connect_queue_skb(struct sock *sk, struct sk_buff *skb)
 	sk->sk_wmem_queued += skb->truesize;
 	sk_mem_charge(sk, skb->truesize);
 	tp->write_seq = tcb->end_seq;
-	tp->packets_out += tcp_skb_pcount(skb);
+	tp->packets_out += 1;
 }
 
 /* Build and send a SYN with data and (cached) Fast Open cookie. However,
@@ -3486,7 +3486,7 @@ static int tcp_send_syn_data(struct sock *sk, struct sk_buff *syn)
 
 	/* data was not sent, put it in write_queue */
 	__skb_queue_tail(&sk->sk_write_queue, syn_data);
-	tp->packets_out -= tcp_skb_pcount(syn_data);
+	tp->packets_out -= 1;
 
 fallback:
 	/* Send a regular SYN with Fast Open cookie request option */
-- 
1.8.3.1

Re: [PATCH net-next] tcp: minor optimization for calculating packets_out in tcp connect

[Eric Dumazet]

On 12/15/2018 01:33 AM, Yafang Shao wrote:
> When we building a syn packet, the tcp_skb_pcount(skb) is always 1,
> which is set in tcp_init_nondata_skb().
> Regarding the syn_data, it is set through
> memcpy(syn_data->cb, syn->cb, sizeof(syn->cb)),
> which is always 1 as well.
> 
> So we don't need to use tcp_skb_pcount(skb), that could give us a
> little improvement.
>

I dunno, I find current code more self-documented.

This is not fast path, so I would suggest we keep it.

Thanks.

Re: [PATCH net-next] tcp: minor optimization for calculating packets_out in tcp connect

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Sat, 15 Dec 2018 04:59:00 -0800

> 
> 
> On 12/15/2018 01:33 AM, Yafang Shao wrote:
>> When we building a syn packet, the tcp_skb_pcount(skb) is always 1,
>> which is set in tcp_init_nondata_skb().
>> Regarding the syn_data, it is set through
>> memcpy(syn_data->cb, syn->cb, sizeof(syn->cb)),
>> which is always 1 as well.
>> 
>> So we don't need to use tcp_skb_pcount(skb), that could give us a
>> little improvement.
>>
> 
> I dunno, I find current code more self-documented.
> 
> This is not fast path, so I would suggest we keep it.

I agree, I won't be applying this.