c2da3f1b71
Waiman reported that on large systems with a large amount of interrupts the readout of /proc/stat takes a long time to sum up the interrupt statistics. In principle this is not a problem. but for unknown reasons some enterprise quality software reads /proc/stat with a high frequency. The reason for this is that interrupt statistics are accounted per cpu. So the /proc/stat logic has to sum up the interrupt stats for each interrupt. The interrupt core provides now a per interrupt summary counter which can be used to avoid the summation loops completely except for interrupts marked PER_CPU which are only a small fraction of the interrupt space if at all. Another simplification is to iterate only over the active interrupts and skip the potentially large gaps in the interrupt number space and just print zeros for the gaps without going into the interrupt core in the first place. Waiman provided test results from a 4-socket IvyBridge-EX system (60-core 120-thread, 3016 irqs) excuting a test program which reads /proc/stat 50,000 times: Before: 18.436s (sys 18.380s) After: 3.769s (sys 3.742s) Reported-by: Waiman Long <longman@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com> Reviewed-by: Waiman Long <longman@redhat.com> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com> Reviewed-by: Davidlohr Bueso <dbueso@suse.de> Cc: Matthew Wilcox <willy@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Kees Cook <keescook@chromium.org> Cc: linux-fsdevel@vger.kernel.org Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Miklos Szeredi <miklos@szeredi.hu> Cc: Daniel Colascione <dancol@google.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Randy Dunlap <rdunlap@infradead.org> Link: https://lkml.kernel.org/r/20190208135021.013828701@linutronix.de |
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| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| firmware | ||
| 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 | ||
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| Kbuild | ||
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| 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.