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Eric Dumazet says: ==================== tcp: do not use tcp_time_stamp for rcv autotuning 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. ==================== Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.