[PATCH v3 00/13] futex: Introducing throughput-optimized futexes

[Waiman Long <Waiman.Long@hpe.com>]

 v2->v3:
  - Use the abbreviation TP for the new futexes instead of TO.
  - Make a number of changes accordingly to review comments from
    ThomasG, PeterZ and MikeG.
  - Breaks the main futex patch into smaller pieces to make them easier
    to review.
  - Integrate the microbenchmark into the "perf bench futex" tool
    so that others can use it too.

 v1->v2:
  - Adds an explicit lock hand-off mechanism.
  - Adds timeout support.
  - Simplifies the required userspace code.
  - Fixes a number of problems in the v1 code.

This patchset introduces a new futex implementation called
throughput-optimized (TP) futexes. It is similar to PI futexes in its
calling convention, but provides better throughput than the wait-wake
futexes by encouraging more lock stealing and optimistic spinning
especially when the lock holders don't sleep and the critical sections
are not very short.

A manpage patch that documents changes to the futex(2) system call
will be sent out separately.

Patch 1 consolidates the duplicated timer setup code.

Patch 2 renames the futex_pi_state structure to futex_state as it
will no longer be specific to the PI futexes. Some futex_pi_state
related functions are also renamed.

Patch 3 adds some helper functions to be used in later patches.

Patch 4 consolidates the codes that need to add or delete futex_state
to pi_state_list.

Patch 5 adds a new type field to the futex_state structure.

Patch 6 changes the futex_hash_bucket to include another list for
futex state objects and a spinlock to guard the new list.

Patch 7 is the core of this patchset and introduction of the new
TP futexes.

Patch 8 enables more robust handling when the futex owners died
unexpectedly.

Patch 9 implements the lock handoff mechanism to prevent lock
starvation.

Patch 10 enables the FUTEX_LOCK call to return a status code to show
how the lock is being acquired.

Patch 11 adds code support the specification of a timeout value in
the FUTEX_LOCK call.

Patch 12 adds a new documentation file about the TP futexes.

Patch 13 adds the futex microbenchmark that was used to produce the
performance data to the "perf bench futex" tool. Others can then use
it to do their own evaluation.

Waiman Long (13):
  futex: Consolidate duplicated timer setup code
  futex: Rename futex_pi_state to futex_state
  futex: Add helpers to get & cmpxchg futex value without lock
  futex: Consolidate pure pi_state_list add & delete codes to helpers
  futex: Add a new futex type field into futex_state
  futex: Allow direct attachment of futex_state objects to hash bucket
  futex: Throughput-optimized (TP) futexes
  futex: Enable robust handling of TP futexes
  futex: Implement lock handoff for TP futexes to prevent lock
    starvation
  futex: Inform FUTEX_LOCK callers on how the lock is acquired
  futex: Add timeout support to TP futexes
  futex, doc: TP futexes document
  perf bench: New microbenchmark for userspace mutex performance

 Documentation/00-INDEX         |    2 +
 Documentation/tp-futex.txt     |  147 +++++++
 include/linux/sched.h          |    4 +-
 include/uapi/linux/futex.h     |    4 +
 kernel/futex.c                 |  943 +++++++++++++++++++++++++++++++++++-----
 tools/perf/bench/Build         |    1 +
 tools/perf/bench/bench.h       |    1 +
 tools/perf/bench/futex-mutex.c |  558 ++++++++++++++++++++++++
 tools/perf/bench/futex.h       |   25 +
 tools/perf/builtin-bench.c     |    4 +
 10 files changed, 1575 insertions(+), 114 deletions(-)
 create mode 100644 Documentation/tp-futex.txt
 create mode 100644 tools/perf/bench/futex-mutex.c