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c5a282e963
This patch aims at reducing ep wq.lock hold times in epoll_wait(2). For the blocking case, there is no need to constantly take and drop the spinlock, which is only needed to manipulate the waitqueue. The call to ep_events_available() is now lockless, and only exposed to benign races. Here, if false positive (returns available events and does not see another thread deleting an epi from the list) we call into send_events and then the list's state is correctly seen. Otoh, if a false negative and we don't see a list_add_tail(), for example, from irq callback, then it is rechecked again before blocking, which will see the correct state. In order for more accuracy to see concurrent list_del_init(), use the list_empty_careful() variant -- of course, this won't be safe against insertions from wakeup. For the overflow list we obviously need to prevent load/store tearing as we don't want to see partial values while the ready list is disabled. [dave@stgolabs.net: forgotten fixlets] Link: http://lkml.kernel.org/r/20181109155258.jxcr4t2pnz6zqct3@linux-r8p5 Link: http://lkml.kernel.org/r/20181108051006.18751-6-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Suggested-by: Jason Baron <jbaron@akamai.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.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.