1fea323ff0
On debug kernels, we call xfs_dir3_leaf_check_int() multiple times on every directory modification. The robust hash ordering checks it does on every entry in the leaf on every call results in a massive CPU overhead which slows down debug kernels by a large amount. We use xfs_dir3_leaf_check_int() for the verifiers as well, so we can't just gut the function to reduce overhead. What we can do, however, is reduce the work it does when it is called from the debug interfaces, just leaving the high level checks in place and leaving the robust validation to the verifiers. This means the debug checks will catch gross errors, but subtle bugs might not be caught until a verifier is run. It is easy enough to restore the existing debug behaviour if the developer needs it (just change a call parameter in the debug code), but overwise the overhead makes testing large directory block sizes on debug kernels very slow. Profile at an unlink rate of ~80k file/s on a 64k block size filesystem before the patch: 40.30% [kernel] [k] xfs_dir3_leaf_check_int 10.98% [kernel] [k] __xfs_dir3_data_check 8.10% [kernel] [k] xfs_verify_dir_ino 4.42% [kernel] [k] memcpy 2.22% [kernel] [k] xfs_dir2_data_get_ftype 1.52% [kernel] [k] do_raw_spin_lock Profile after, at an unlink rate of ~125k files/s (+50% improvement) has largely dropped the leaf verification debug overhead out of the profile. 16.53% [kernel] [k] __xfs_dir3_data_check 12.53% [kernel] [k] xfs_verify_dir_ino 7.97% [kernel] [k] memcpy 3.36% [kernel] [k] xfs_dir2_data_get_ftype 2.86% [kernel] [k] __pv_queued_spin_lock_slowpath Create shows a similar change in profile and a +25% improvement in performance. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Darrick J. Wong <djwong@kernel.org> |
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| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| 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 | ||
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.