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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.
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