864e5c0907
When TCP implements its own pacing (when no fq packet scheduler is used), it is arming high resolution timer after a packet is sent. But in many cases (like TCP_RR kind of workloads), this high resolution timer expires before the application attempts to write the following packet. This overhead also happens when the flow is ACK clocked and cwnd limited instead of being limited by the pacing rate. This leads to extra overhead (high number of IRQ) Now tcp_wstamp_ns is reserved for the pacing timer only (after commit "tcp: do not change tcp_wstamp_ns in tcp_mstamp_refresh"), we can setup the timer only when a packet is about to be sent, and if tcp_wstamp_ns is in the future. This leads to a ~10% performance increase in TCP_RR workloads. Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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 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.