Re: [PATCH net-next] tcp: minor optimization in tcp ack fast path processing

On Wed, Nov 7, 2018 at 11:16 PM Eric Dumazet [off-list ref] wrote:

On 11/07/2018 03:20 AM, Yafang Shao wrote:

quoted

Bitwise operation is a little faster.

quoted

So I replace after() with (flag & FLAG_SND_UNA_ADVANCED) as this flag is
already set before.

Cc: Joe Perches <joe@perches.com>
Signed-off-by: Yafang Shao <redacted>
---
 net/ipv4/tcp_input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2868ef2..0167015 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c

@@ -3610,7 +3610,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
      if (flag & FLAG_UPDATE_TS_RECENT)
              tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);

-     if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
+     if (!(flag & FLAG_SLOWPATH) && (flag & FLAG_SND_UNA_ADVANCED)) {
              /* Window is constant, pure forward advance.
               * No more checks are required.
               * Note, we use the fact that SND.UNA>=SND.WL2.

What about reducing this to a single conditional jump ?

if ((flag & (FLAG_SLOWPATH | FLAG_SND_UNA_ADVANCED)) == FLAG_SND_UNA_ADVANCED)  {

That's better.
Will change it.


Thanks
Yafang