Subject: [PATCH net-next] net: sk_pacing_shift_update() helper

From: Eric Dumazet <[email-masked]>
Date: Tue, 12 Dec 2017 06:34:19 -0800

From: Eric Dumazet <[email-masked]>

In commit 3a9b76fd0db9 ("tcp: allow drivers to tweak TSQ logic")
I gave a code sample to set sk->sk_pacing_shift that was not complete.

Better add a helper that can be used by drivers without worries,
and maybe amended in the future.

A wifi driver might use it from its ndo_start_xmit()

Following call would setup TCP to allow up to ~8ms of queued data per
flow.

sk_pacing_shift_update(skb->sk, 7);

Signed-off-by: Eric Dumazet <[email-masked]>
---
 include/net/sock.h |   11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/include/net/sock.h b/include/net/sock.h
index 9155da42269208b358df8535b14dfd3dba509365..9a9047268d375496bccc954d03ec20baf4177fd3 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2407,4 +2407,15 @@ static inline int sk_get_rmem0(const struct sock *sk, const struct proto *proto)
 	return *proto->sysctl_rmem;
 }
 
+/* Default TCP Small queue budget is ~1 ms of data (1sec >> 10)
+ * Some wifi drivers need to tweak it to get more chunks.
+ * They can use this helper from their ndo_start_xmit()
+ */
+static inline void sk_pacing_shift_update(struct sock *sk, int val)
+{
+	if (!sk || !sk_fullsock(sk) || sk->sk_pacing_shift == val)
+		return;
+	sk->sk_pacing_shift = val;
+}
+
 #endif	/* _SOCK_H */