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On x86_64, frag_* fields of struct page_pool are scattered across two cachelines despite the summary size of 24 bytes. All three fields are used in pretty much the same places, but the last field, ::frag_users, is pushed out to the next CL, provoking unwanted false-sharing on hotpath (frags allocation code). There are some holes and cold members to move around. Move frag_* one block up, placing them right after &page_pool_params perfectly at the beginning of CL2. This doesn't do any meaningful to the second block, as those are some destroy-path cold structures, and doesn't do anything to ::alloc_stats, which still starts at 200-byte offset, 8 bytes after CL3 (still fitting into 1 cacheline). On my setup, this yields 1-2% of Mpps when using PP frags actively. When it comes to 32-bit architectures with 32-byte CL: &page_pool_params plus ::pad is 44 bytes, the block taken care of is 16 bytes within one CL, so there should be at least no regressions from the actual change. ::pages_state_hold_cnt is not related directly to that triple, but is paired currently with ::frags_offset and decoupling them would mean either two 4-byte holes or more invasive layout changes. Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com> Link: https://lore.kernel.org/r/20230804180529.2483231-4-aleksander.lobakin@intel.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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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.