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Each time some payload is consumed by user space (recvmsg() and friends), TCP calls tcp_rcv_space_adjust() to run DRS algorithm to check if an increase of sk->sk_rcvbuf is needed. This function is based on time sampling, and currently calls tcp_mstamp_refresh(tp), which is a wrapper around ktime_get_ns(). ktime_get_ns() has a high cost on some platforms. 100+ cycles for rdtscp on AMD EPYC Turin for instance. We do not have to refresh tp->tcp_mpstamp, using the last cached value is enough. We only need to refresh it from __tcp_cleanup_rbuf() if an ACK must be sent (this is a rare event). Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com> Link: https://patch.msgid.link/20251024120707.3516550-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
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.