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struct device is big, around 760 bytes on x86_64. It's not a critical structure, but it is embedded everywhere, so making it smaller is always a good thing. With a recent patch that moved a field from struct device to the private structure, some benchmarks showed a very odd regression, despite this structure having nothing to do with those benchmarks. That caused me to look into the layout of the structure. Using 'pahole', it showed a number of holes and ways that the structure could be reordered in order to align some cachelines better, as well as reduce the size of the overall structure. Move 'struct kobj' to the start of the structure, to keep that access in the first cacheline, and try to organize things a bit more compactly where possible By doing these few moves, the result removes at least 8 bytes from 'struct device' on a 64bit system. Given we know there are systems with at least 30k devices in memory at once, every little byte counts, and this change could be a savings of 240k of kernel memory for them. On "normal" systems the overall memory savings would be much less. Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com> Cc: Johan Hovold <johan@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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| certs | ||
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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.