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Re: C++20 futex with heavy contention slower than mutex

From Michael S <already5chosen@yahoo.com>
Newsgroups comp.lang.c++
Subject Re: C++20 futex with heavy contention slower than mutex
Date 2024-04-01 12:18 +0300
Organization A noiseless patient Spider
Message-ID <20240401121800.00000d25@yahoo.com> (permalink)
References <uu6eqs$ab8u$1@raubtier-asyl.eternal-september.org>

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On Fri, 29 Mar 2024 14:14:11 +0100
Bonita Montero <Bonita.Montero@gmail.com> wrote:

> The following program simulates constant locking und unlocking of one
> to jthread::hardware_concurrency() threadas with a std::mutex and a
> futex. On my 16 core / 32 thread Zen4 system a futex is faster up to
> 5 threads constantly contending, but beyond the CPU time of the futex
> explodes and the conventional mutex is faster with Windows as and with
> Linux.
>

In case of heavy contention what to consider 'faster' is not at all
obvious.

On lightly loaded system with more cores than work to do (a typical
client) 'faster' means faster forward progress of group of contending
threads. Achieved by very long polling before switching to wait,
probably up to several tens of usec and by hyperactive tickless OS
scheduler.

On heavily loaded system with much more work to do than available
cores, 'faster' means more work done by unrelated threads and processes.
Achieved by very short polling before switching to wait, probably less
than 500 nsec and by 'passive' OS scheduler that rarely intervenes
outside of clock tick.

And of course there are cases in the middle.

And then traditional HPC with MPI that is completely different kettle of
fish.

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C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-29 14:14 +0100
  Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-29 15:28 -0700
    Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-29 15:30 -0700
      Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-29 16:29 -0700
        Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-29 19:46 -0700
        Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-30 09:25 +0100
          Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-30 11:51 -0700
            Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-30 12:02 -0700
            Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-30 21:18 +0100
              Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-31 13:11 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-01 08:32 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-31 23:40 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-01 10:57 +0200
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-01 11:01 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-01 12:27 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-02 04:37 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-12 14:16 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-13 03:00 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 12:26 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 06:19 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 21:26 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 06:30 +0200
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 06:34 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 22:21 -0700
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 22:21 -0700
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 22:22 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 07:30 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 22:32 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 07:36 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 22:42 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 07:46 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 22:48 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 11:25 +0200
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 15:12 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-14 12:02 -0700
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-14 12:06 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-14 22:57 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-14 20:23 -0700
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-14 20:26 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-15 06:15 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-14 22:03 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-15 08:20 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-15 12:08 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-16 06:32 +0200
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-16 11:31 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-16 14:07 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-17 10:24 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-17 11:48 -0700
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-17 11:52 -0700
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-16 14:14 -0700
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-18 15:12 +0200
                Re: C++20 futex with heavy contention slower than mutex Richard Damon <richard@damon-family.org> - 2024-04-18 22:03 -0400
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-19 06:18 +0200
                Re: C++20 futex with heavy contention slower than mutex scott@slp53.sl.home (Scott Lurndal) - 2024-04-19 13:41 +0000
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-19 15:44 +0200
                Re: C++20 futex with heavy contention slower than mutex scott@slp53.sl.home (Scott Lurndal) - 2024-04-19 14:48 +0000
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-19 17:32 +0200
                Re: C++20 futex with heavy contention slower than mutex scott@slp53.sl.home (Scott Lurndal) - 2024-04-19 18:27 +0000
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-20 04:48 +0200
                Re: C++20 futex with heavy contention slower than mutex scott@slp53.sl.home (Scott Lurndal) - 2024-04-20 15:16 +0000
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-20 17:36 +0200
                Re: C++20 futex with heavy contention slower than mutex Richard Damon <richard@damon-family.org> - 2024-04-19 23:00 -0400
                Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-04-20 06:11 +0200
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-14 12:10 -0700
                Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-13 22:46 -0700
            Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-31 22:01 -0700
              Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-31 22:02 -0700
    Re: C++20 futex with heavy contention slower than mutex Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-30 05:18 +0100
  Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-30 12:00 -0700
  Re: C++20 futex with heavy contention slower than mutex Michael S <already5chosen@yahoo.com> - 2024-04-01 12:18 +0300
    Re: C++20 futex with heavy contention slower than mutex "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-04-04 19:56 -0700

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