netdev - Re: [PATCH net-next] tcp: implement TSQ for retransmits

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Message-Id: <20160922.024454.403661058785255364.davem@davemloft.net>
Date:   Thu, 22 Sep 2016 02:44:54 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     ncardwell@...gle.com, ycheng@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tcp: implement TSQ for retransmits

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 20 Sep 2016 22:45:58 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> We saw sch_fq drops caused by the per flow limit of 100 packets and TCP
> when dealing with large cwnd and bursts of retransmits.
> 
> Even after increasing the limit to 1000, and even after commit
> 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit time"),
> we can still have these drops.
> 
> Under certain conditions, TCP can spend a considerable amount of
> time queuing thousands of skbs in a single tcp_xmit_retransmit_queue()
> invocation, incurring latency spikes and stalls of other softirq
> handlers.
> 
> This patch implements TSQ for retransmits, limiting number of packets
> and giving more chance for scheduling packets in both ways.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>

Applied.