mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/
synced 2026-11-10 20:48:12 +00:00
No description
- C 96.8%
- Assembly 0.9%
- Rust 0.7%
- Shell 0.6%
- Python 0.5%
- Other 0.3%
7e340f4fadAlexandre Ghiti <alexghiti@rivosinc.com> says: In RISC-V, after a new mapping is established, a sfence.vma needs to be emitted for different reasons: - if the uarch caches invalid entries, we need to invalidate it otherwise we would trap on this invalid entry, - if the uarch does not cache invalid entries, a reordered access could fail to see the new mapping and then trap (sfence.vma acts as a fence). We can actually avoid emitting those (mostly) useless and costly sfence.vma by handling the traps instead: - for new kernel mappings: only vmalloc mappings need to be taken care of, other new mapping are rare and already emit the required sfence.vma if needed. That must be achieved very early in the exception path as explained in patch 3, and this also fixes our fragile way of dealing with vmalloc faults. - for new user mappings: Svvptc makes update_mmu_cache() a no-op but we can take some gratuitous page faults (which are very unlikely though). Patch 1 and 2 introduce Svvptc extension probing. On our uarch that does not cache invalid entries and a 6.5 kernel, the gains are measurable: * Kernel boot: 6% * ltp - mmapstress01: 8% * lmbench - lat_pagefault: 20% * lmbench - lat_mmap: 5% Here are the corresponding numbers of sfence.vma emitted: * Ubuntu boot to login: Before: ~630k sfence.vma After: ~200k sfence.vma * ltp - mmapstress01 Before: ~45k After: ~6.3k * lmbench - lat_pagefault Before: ~665k After: 832 (!) * lmbench - lat_mmap Before: ~546k After: 718 (!) Thanks to Ved and Matt Evans for triggering the discussion that led to this patchset! * b4-shazam-merge: riscv: Stop emitting preventive sfence.vma for new userspace mappings with Svvptc riscv: Stop emitting preventive sfence.vma for new vmalloc mappings dt-bindings: riscv: Add Svvptc ISA extension description riscv: Add ISA extension parsing for Svvptc Link: https://lore.kernel.org/r/20240717060125.139416-1-alexghiti@rivosinc.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com> |
History
|
|
|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .rustfmt.toml | ||
| 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 reStructuredText 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.