netdev - Re: [PATCH net-next] tcp: refine pacing rate determination

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Message-Id: <20150825.113404.916165871303626879.davem@davemloft.net>
Date:	Tue, 25 Aug 2015 11:34:04 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, ncardwell@...gle.com, ycheng@...gle.com
Subject: Re: [PATCH net-next] tcp: refine pacing rate determination

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Fri, 21 Aug 2015 17:38:02 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> When TCP pacing was added back in linux-3.12, we chose
> to apply a fixed ratio of 200 % against current rate,
> to allow probing for optimal throughput even during
> slow start phase, where cwnd can be doubled every other gRTT.
> 
> At Google, we found it was better applying a different ratio
> while in Congestion Avoidance phase.
> This ratio was set to 120 %.
> 
> We've used the normal tcp_in_slow_start() helper for a while,
> then tuned the condition to select the conservative ratio
> as soon as cwnd >= ssthresh/2 :
> 
> - After cwnd reduction, it is safer to ramp up more slowly,
>   as we approach optimal cwnd.
> - Initial ramp up (ssthresh == INFINITY) still allows doubling
>   cwnd every other RTT.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.
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