On Fri, 2015-02-06 at 05:40 -0800, Eric Dumazet wrote:

tcp_wfree() could maintain in tp->tx_completion_delay_ms an EWMA
of TX completion delay. But this would require yet another expensive
call to ktime_get() if HZ < 1000.

Then tcp_write_xmit() could use it to adjust :

   limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 9);

to

   amount = (2 + tp->tx_completion_delay_ms) * sk->sk_pacing_rate 

   limit = max(2 * skb->truesize, amount / 1000);

I'll cook a patch.

Hmm... doing this in all protocols would be too expensive,
and we do not want to include time spent in qdiscs.

wifi could eventually do that, providing in skb->tx_completion_delay_us
the time spent in wifi driver.

This way, we would have no penalty for network devices doing normal skb
orphaning (loopback interface, ethernet, ...)