f21a3c4803
Sometimes, we may call tcp receive zerocopy when inq is 0, or inq < PAGE_SIZE, or inq is generally small enough that it is cheaper to copy rather than remap pages. In these cases, we may want to either return early (inq=0) or attempt to use the provided copy buffer to simply copy the received data. This allows us to save both system call overhead and the latency of acquiring mmap_sem in read mode for cases where it would be useless to do so. This patchset enables this behaviour by: 1. Returning quickly if inq is 0. 2. Attempting to perform a regular copy if a hybrid copybuffer is provided and it is large enough to absorb all available bytes. 3. Return quickly if no such buffer was provided and there are less than PAGE_SIZE bytes available. For small RPC ping-pong workloads, normally we would have 1 getsockopt(), 1 recvmsg() and 1 sendmsg() call per RPC. With this change, we remove the recvmsg() call entirely, reducing the syscall overhead by about 33%. In testing with small (hundreds of bytes) RPC traffic, this yields a syscall reduction of about 33% and an efficiency gain of about 3-5% when defined as QPS/CPU Util. Signed-off-by: Arjun Roy <arjunroy@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: Soheil Hassas Yeganeh <soheil@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 Restructured Text 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.