netdev - Re: [PATCH net-next 00/10] tcp: do not use tcp_time

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Message-Id: <20170426.144458.2055504829054846592.davem@davemloft.net>
Date:   Wed, 26 Apr 2017 14:44:58 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, soheil@...gle.com, eric.dumazet@...il.com
Subject: Re: [PATCH net-next 00/10] tcp: do not use tcp_time_stamp for rcv
 autotuning

From: Eric Dumazet <edumazet@...gle.com>
Date: Tue, 25 Apr 2017 10:15:31 -0700

> Some devices or linux distributions use HZ=100 or HZ=250
> 
> TCP receive buffer autotuning has poor behavior caused by this choice.
> Since autotuning happens after 4 ms or 10 ms, short distance flows
> get their receive buffer tuned to a very high value, but after an initial
> period where it was frozen to (too small) initial value.
> 
> With BBR (or other CC allowing to increase BDP), we are willing to
> increase tcp_rmem[2], but this receive autotuning defect is a blocker
> for hosts dealing with gazillions of TCP flows in the data centers,
> since many of them have inflated RCVBUF. Risk of OOM is too high.
> 
> Note that TSO autodefer, tcp cubic, and TCP TS options (RFC 7323)
> also suffer from our dependency to jiffies (via tcp_time_stamp).
> 
> We have ongoing efforts to improve all that in the future.

Looks great, series applied, thanks Eric.