netdev - Re: [PATCH net-next 0/3] tcp: improving RACK cpu performance

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Message-Id: <20171005.212612.1580802624897584218.davem@davemloft.net>
Date:   Thu, 05 Oct 2017 21:26:12 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     ycheng@...gle.com
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/3] tcp: improving RACK cpu performance

From: Yuchung Cheng <ycheng@...gle.com>
Date: Wed,  4 Oct 2017 12:59:57 -0700

> This patch set improves the CPU consumption of the RACK TCP loss
> recovery algorithm, in particular for high-speed networks. Currently,
> for every ACK in recovery RACK can potentially iterate over all sent
> packets in the write queue. On large BDP networks with non-trivial
> losses the RACK write queue walk CPU usage becomes unreasonably high.
> 
> This patch introduces a new queue in TCP that keeps only skbs sent and
> not yet (s)acked or marked lost, in time order instead of sequence
> order.  With that, RACK can examine this time-sorted list and only
> check packets that were sent recently, within the reordering window,
> per ACK. This is the fastest way without any write queue walks. The
> number of skbs examined per ACK is reduced by orders of magnitude.

That's a pretty risky way to implement the second SKB list.... but
you avoided making sk_buff larger so what can I say :-)

Series applied, thank.