Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak

From	"Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups	comp.lang.c++
Subject	Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak
Date	2021-12-08 00:59 -0800
Organization	A noiseless patient Spider
Message-ID	<sops5m$8r4$2@dont-email.me> (permalink)
References	(4 earlier) <soo8au$26q$1@dont-email.me> <H0OrJ.110234$Z0a.15989@fx17.iad> <sooam4$j94$1@dont-email.me> <AoOrJ.102436$SW5.42759@fx45.iad> <LyOrJ.56060$no7.16842@fx15.iad>

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On 12/7/2021 11:25 AM, Scott Lurndal wrote:
> scott@slp53.sl.home (Scott Lurndal) writes:
>> Bonita Montero <Bonita.Montero@gmail.com> writes:
>>> Am 07.12.2021 um 19:49 schrieb Scott Lurndal:
>>
>>>
>>>> How do you know?
>>>
>>> Because this would be slower since the lock-modifications
>>> woudln't be done in the L1-caches but in far memory. That's
>>> just a silly idea.
>>
>> Hello, it's a cache-coherent multiprocessor.   You need to
>> fetch it exclusively into the L1 first, so instead of sending the fetch
>> (or invalidate if converting a shared line to owned),
>> you send the atomic op and it gets handled atomically at
>> the far end (e.g. LLC, PCI express device, SoC coprocessor)
>> saving the interconnect (mesh, ring, whatever) bandwidth and
>> the round-trip time between L1 and LLC and reducing contention
>> for the line.
>>
>> If it's already in the L1 cache, then the processor will
>> automatically treat it as a near-atomic, this is expected
>> to be a rare case with correctly designed atomic usage.
> 
> In case you need a public reference for a shipping processor:
> 
> https://developer.arm.com/documentation/102099/0000/L1-data-memory-system/Instruction-implementation-in-the-L1-data-memory-system
> 


You have encountered the rabbit hole of Bonita! I have proved her/it 
wrong several times. No good, goes nowhere.

Thread

Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-05 18:13 +0100
  Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-05 19:56 +0000
    Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-12-05 15:22 -0800
      Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-05 23:43 +0000
        Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-12-05 19:31 -0800
      Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-06 06:26 +0100
    Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-06 06:24 +0100
      Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Ben Bacarisse <ben.usenet@bsb.me.uk> - 2021-12-06 10:45 +0000
        Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-06 13:09 +0100
  Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-06 06:27 +0100
  Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak scott@slp53.sl.home (Scott Lurndal) - 2021-12-06 18:02 +0000
    Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-07 06:27 +0100
      Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak scott@slp53.sl.home (Scott Lurndal) - 2021-12-07 18:06 +0000
        Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-07 19:14 +0100
          Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak scott@slp53.sl.home (Scott Lurndal) - 2021-12-07 18:49 +0000
            Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-07 19:54 +0100
              Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak scott@slp53.sl.home (Scott Lurndal) - 2021-12-07 19:14 +0000
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak scott@slp53.sl.home (Scott Lurndal) - 2021-12-07 19:25 +0000
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-08 09:50 +0100
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2021-12-08 00:59 -0800
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-08 15:41 +0100
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak scott@slp53.sl.home (Scott Lurndal) - 2021-12-08 15:48 +0000
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Bonita Montero <Bonita.Montero@gmail.com> - 2021-12-08 17:35 +0100
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Öö Tiib <ootiib@hot.ee> - 2021-12-08 10:57 -0800
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Manfred <noname@add.invalid> - 2021-12-09 00:27 +0100
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak Juha Nieminen <nospam@thanks.invalid> - 2021-12-09 06:30 +0000
                Re: Little program to test concurrency of .fetch_add and .compare_exchange_weak David Brown <david.brown@hesbynett.no> - 2021-12-08 09:08 +0100

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