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tcp_rcv_space_adjust is called every time data is copied to user space, introducing a tcp tracepoint for which could show us when the packet is copied to user. When a tcp packet arrives, tcp_rcv_established() will be called and with the existed tracepoint tcp_probe we could get the time when this packet arrives. Then this packet will be copied to user, and tcp_rcv_space_adjust will be called and with this new introduced tracepoint we could get the time when this packet is copied to user. With these two tracepoints, we could figure out whether the user program processes this packet immediately or there's latency. Hence in the printk message, sk_cookie is printed as a key to relate tcp_rcv_space_adjust with tcp_probe. Maybe we could export sockfd in this new tracepoint as well, then we could relate this new tracepoint with epoll/read/recv* tracepoints, and finally that could show us the whole lifespan of this packet. But we could also implement that with pid as these functions are executed in process context. Signed-off-by: Yafang Shao <laoar.shao@gmail.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.