From: Thomas Gleixner <tglx@linutronix.de>
To: LKML <linux-kernel@vger.kernel.org>
Subject: [patch V2 0/7] Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Linus Torvalds <torvalds@linux-foundation.org>, Darren Hart <darren@dvhart.com>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>, Michael Kerrisk <mtk.manpages@googlemail.com>, Davidlohr Bueso <dave@stgolabs.net>, Chris Mason <clm@fb.com>, Carlos O'Donell <carlos@redhat.com>, Torvald Riegel <triegel@redhat.com>, Eric Dumazet <edumazet@google.com>
Date: Thu, 05 May 2016 19:03:37 -0000 [thread overview]
Message-ID: <20160505170339.026555108@linutronix.de> (raw)
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].
Thanks,
tglx
[1] http://lkml.kernel.org/r/20160428161742.363543816@linutronix.de
----
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(-)
next reply other threads:[~2016-05-05 19:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-05 19:03 Thomas Gleixner [this message]
2016-05-05 19:03 ` [patch V2 1/7] futex: Add some more function commentry Thomas Gleixner
2016-05-05 19:03 ` [patch V2 2/7] futex: Hash private futexes per process Thomas Gleixner
2016-05-05 19:03 ` [patch V2 3/7] futex: Add op for hash preallocation Thomas Gleixner
2016-05-05 19:03 ` [patch V2 4/7] futex: Add sysctl knobs for process private hash Thomas Gleixner
2016-05-05 19:03 ` [patch V2 6/7] perf/bench/futex-hash: Support preallocate hash table Thomas Gleixner
2016-05-05 19:03 ` [patch V2 5/7] perf/bench/futex-hash: Support NUMA Thomas Gleixner
2016-05-05 19:03 ` [patch V2 7/7] futex.2: Document hash preallocation opcode Thomas Gleixner
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