[patch V2 0/7] futex: Add support for process private hashing

From: Thomas Gleixner
Date: Thu May 05 2016 - 16:45:57 EST

The standard futex mechanism in the Linux kernel uses a global hash to store
transient state. Collisions on that hash can lead to performance degradation
and on real-time enabled kernels to unbound priority inversions.

This new attempt to solve the issue does not require user space changes and
operates transparently. On the first futex operation of a process the kernel
allocates a hash private to the process. All process private futexes are
hashed in this hash. Process shared futexes still use the global hash.

For RT applications and pathological use cases a new futex op is provided
which allows the application to preallocate and thereby size the process
private hash.

The last two patches add support to the perf futex-hash benchmark so test can
be run on nodes and the preallocation sizing can be tested.

The last patch contains a first update for the futex man page.

The difference vs. V1 of this series is that it uses hash_long() now that the
hash_64 implementation has been fixed in mainline. The performance numbers are
more or less the same as with V1 [1].



[1] http://lkml.kernel.org/r/20160428161742.363543816@xxxxxxxxxxxxx

Documentation/sysctl/kernel.txt | 17 +++
b/include/linux/futex_types.h | 12 ++
include/linux/futex.h | 39 +++++--
include/linux/mm_types.h | 4
include/uapi/linux/futex.h | 1
init/Kconfig | 4
kernel/fork.c | 3
kernel/futex.c | 215 +++++++++++++++++++++++++++++++++++++++-
kernel/sysctl.c | 21 +++
tools/perf/bench/Build | 4
tools/perf/bench/futex-hash.c | 101 ++++++++++++++++--
tools/perf/bench/futex.h | 5
12 files changed, 403 insertions(+), 23 deletions(-)