netdev - Re: [PATCH net-next] tcp: batch calls to sk_flush

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Message-Id: <20190809.110705.591778512450074017.davem@davemloft.net>
Date:   Fri, 09 Aug 2019 11:07:05 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, soheil@...gle.com
Subject: Re: [PATCH net-next] tcp: batch calls to sk_flush_backlog()

From: Eric Dumazet <edumazet@...gle.com>
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 <soheil@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.