mainlining shenanigans
0fa809ca7f
The qspinlock code supports up to 4 levels of slowpath nesting using four per-CPU mcs_spinlock structures. For 64-bit architectures, they fit nicely in one 64-byte cacheline. For para-virtualized (PV) qspinlocks it needs to store more information in the per-CPU node structure than there is space for. It uses a trick to use a second cacheline to hold the extra information that it needs. So PV qspinlock needs to access two extra cachelines for its information whereas the native qspinlock code only needs one extra cacheline. Freshly added counter profiling of the qspinlock code, however, revealed that it was very rare to use more than two levels of slowpath nesting. So it doesn't make sense to penalize PV qspinlock code in order to have four mcs_spinlock structures in the same cacheline to optimize for a case in the native qspinlock code that rarely happens. Extend the per-CPU node structure to have two more long words when PV qspinlock locks are configured to hold the extra data that it needs. As a result, the PV qspinlock code will enjoy the same benefit of using just one extra cacheline like the native counterpart, for most cases. [ mingo: Minor changelog edits. ] Signed-off-by: Waiman Long <longman@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will.deacon@arm.com> Link: http://lkml.kernel.org/r/1539697507-28084-2-git-send-email-longman@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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| drivers | ||
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| usr | ||
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| .clang-format | ||
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| .get_maintainer.ignore | ||
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| 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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.