From: Eric Dumazet <[email protected]>
Date: Fri, 9 Aug 2019 05:04:47 -0700
> Starting from commit d41a69f1d390 ("tcp: make tcp_sendmsg() aware of socket
> backlog")
> loopback flows got hurt, because for each skb sent, the socket receives an
> immediate ACK and sk_flush_backlog() causes extra work.
>
> Intent was to not let the backlog grow too much, but we went a bit too far.
>
> We can check the backlog every 16 skbs (about 1MB chunks)
> to increase TCP over loopback performance by about 15 %
>
> Note that the call to sk_flush_backlog() handles a single ACK,
> thanks to coalescing done on backlog, but cleans the 16 skbs
> found in rtx rb-tree.
>
> Reported-by: Soheil Hassas Yeganeh <[email protected]>
> Signed-off-by: Eric Dumazet <[email protected]>
Applied.
