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Re: Idea for spin-wait loops

From Michael S <already5chosen@yahoo.com>
Newsgroups comp.lang.c++
Subject Re: Idea for spin-wait loops
Date 2024-03-27 17:09 +0200
Organization A noiseless patient Spider
Message-ID <20240327180957.000049c7@yahoo.com> (permalink)
References (2 earlier) <utnfoq$3s1eu$1@dont-email.me> <utoho8$6p4u$2@raubtier-asyl.eternal-september.org> <uttd1r$1ervd$1@dont-email.me> <utu71j$1obp8$1@raubtier-asyl.eternal-september.org> <utv9l7$2anr0$2@dont-email.me>

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On Tue, 26 Mar 2024 13:02:47 -0700
"Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> wrote:

> On 3/26/2024 3:12 AM, Bonita Montero wrote:
> > Am 26.03.2024 um 03:48 schrieb Chris M. Thomasson:  
> >> On 3/23/2024 11:38 PM, Bonita Montero wrote:  
> >>> Am 23.03.2024 um 21:58 schrieb Chris M. Thomasson:  
> >>>>
> >>>> MWAIT?  
> >>>
> >>> MWAIT has no timeout.
> >>>  
> >>
> >> Not sure how important it would be for MWAIT to have a timeout...
> >> You are referring to user space, right?  
> > 
> > MWAIT could be used for limited spinning like glibc's pthread_mutex
> > is capable. The advantage of a MWAIT with timout would be much less
> > interconnect-traffic compared to polling.
> >   
> 
> MWAIT is meant to get around polling?

I don't know what you mean by 'get around'.
The main point of original Monitor/MWAIT is to allow to one SMT thread
to do polling on memory address in a way that consumes almost no core's
execution resources thus allowing to the other SMT thread(s) of the
same core to run faster. The sort of more intelligent PAUSE.
In the absence of other SMT threads the main advantage of polling
loop with Monitor/MWAIT vs simple tight polling loop (STPL) is reduced
power consumption.
As far as cache coherence traffic (CCT) is concerned, Monitor/MWAIT
polling loop provides virtually no advantage relatively to STPL. Both
are quite efficient from CCT perspective, at least as long as programmer
does not do anything stupid.

Later on Intel invented 'MWAIT for Power Management' that has slightly
different objectives. But that is O.T.

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Idea for spin-wait loops Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-23 17:53 +0100
  Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-23 13:52 -0700
    Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-23 13:58 -0700
      Re: Idea for spin-wait loops Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-24 07:38 +0100
        Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-25 19:48 -0700
          Re: Idea for spin-wait loops Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-26 11:12 +0100
            Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-26 13:02 -0700
              Re: Idea for spin-wait loops Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-26 21:23 +0100
                Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-26 13:30 -0700
                Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-26 13:31 -0700
                Re: Idea for spin-wait loops Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-27 10:18 +0100
              Re: Idea for spin-wait loops Michael S <already5chosen@yahoo.com> - 2024-03-27 17:09 +0200
                Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-27 12:58 -0700
    Re: Idea for spin-wait loops Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-24 07:37 +0100
      Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-24 12:33 -0700
    Re: Idea for spin-wait loops scott@slp53.sl.home (Scott Lurndal) - 2024-03-24 20:43 +0000
      Re: Idea for spin-wait loops Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-25 07:23 +0100
      Re: Idea for spin-wait loops Michael S <already5chosen@yahoo.com> - 2024-03-25 14:34 +0200
        Re: Idea for spin-wait loops Michael S <already5chosen@yahoo.com> - 2024-03-25 19:11 +0200
        Re: Idea for spin-wait loops Bonita Montero <Bonita.Montero@gmail.com> - 2024-03-25 18:53 +0100
          Re: Idea for spin-wait loops "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2024-03-26 13:13 -0700

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