b860a1b964
Practical experience (and advice from Alexei) tell us that bitfields in structs lead to un-optimized assembly code. I've verified this change does lead to better x86_64 assembly, both via objdump and playing with code snippets in godbolt.org. Using scripts/bloat-o-meter shows the code size is reduced with 24 bytes for xdp_convert_buff_to_frame() that gets inlined e.g. in i40e_xmit_xdp_tx_ring() which were used for microbenchmarking. Microbenchmarking results do show improvements, but very small and varying between 0.5 to 2 nanosec improvement per packet. The member @metasize is changed from u8 to u32. Future users of this area could split this into two u16 fields. I've also benchmarked with two u16 fields showing equal performance gains and code size reduction. The moved member @frame_sz doesn't change sizeof struct due to existing padding. Like xdp_buff member @frame_sz is placed next to @flags, which allows compiler to optimize assignment of these. Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Link: https://lore.kernel.org/r/166393728005.2213882.4162674859542409548.stgit@firesoul 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.