netdev - Re: [PATCH v7 net-next 2/2] tcp: switch rtt estimations to usec resolution

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Message-Id: <20140226.170439.506202474296777480.davem@davemloft.net>
Date:	Wed, 26 Feb 2014 17:04:39 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	stephen@...workplumber.org, ja@....bg, ycheng@...gle.com,
	netdev@...r.kernel.org, ncardwell@...gle.com, brakmo@...gle.com
Subject: Re: [PATCH v7 net-next 2/2] tcp: switch rtt estimations to usec
 resolution

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Wed, 26 Feb 2014 14:02:48 -0800

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Upcoming congestion controls for TCP require usec resolution for RTT
> estimations. Millisecond resolution is simply not enough these days.
> 
> FQ/pacing in DC environments also require this change for finer control
> and removal of bimodal behavior due to the current hack in
> tcp_update_pacing_rate() for 'small rtt'
> 
> TCP_CONG_RTT_STAMP is no longer needed.
> 
> As Julian Anastasov pointed out, we need to keep user compatibility :
> tcp_metrics used to export RTT and RTTVAR in msec resolution,
> so we added RTT_US and RTTVAR_US. An iproute2 patch is needed
> to use the new attributes if provided by the kernel.
> 
 ...
> With help from Julian Anastasov, Stephen Hemminger and Yuchung Cheng
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Acked-by: Neal Cardwell <ncardwell@...gle.com>

Applied, thanks everyone.
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