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Date: Thu, 08 Sep 2016 17:26:33 -0700 (PDT)
From: David Miller <davem@...emloft.net>
To: eric.dumazet@...il.com
Cc: netdev@...r.kernel.org, wygivan@...gle.com, ycheng@...gle.com,
ncardwell@...gle.com, ilpo.jarvinen@...sinki.fi
Subject: Re: [PATCH net-next] tcp: use an RB tree for ooo receive queue
From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 07 Sep 2016 14:49:28 -0700
> From: Yaogong Wang <wygivan@...gle.com>
>
> Over the years, TCP BDP has increased by several orders of magnitude,
> and some people are considering to reach the 2 Gbytes limit.
>
> Even with current window scale limit of 14, ~1 Gbytes maps to ~740,000
> MSS.
>
> In presence of packet losses (or reorders), TCP stores incoming packets
> into an out of order queue, and number of skbs sitting there waiting for
> the missing packets to be received can be in the 10^5 range.
>
> Most packets are appended to the tail of this queue, and when
> packets can finally be transferred to receive queue, we scan the queue
> from its head.
>
> However, in presence of heavy losses, we might have to find an arbitrary
> point in this queue, involving a linear scan for every incoming packet,
> throwing away cpu caches.
>
> This patch converts it to a RB tree, to get bounded latencies.
>
> Yaogong wrote a preliminary patch about 2 years ago.
> Eric did the rebase, added ofo_last_skb cache, polishing and tests.
>
> Tested with network dropping between 1 and 10 % packets, with good
> success (about 30 % increase of throughput in stress tests)
>
> Next step would be to also use an RB tree for the write queue at sender
> side ;)
>
> Signed-off-by: Yaogong Wang <wygivan@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
The sooner this gets applied the sooner it gets tested and any remaining
bugs discovered and fixed.
Applied, thanks Eric.
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