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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: comp.arch
Subject: Re: arm ldxr/stxr vs cas
Date: Mon, 2 Sep 2024 11:58:35 -0700
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On 9/2/2024 11:55 AM, Chris M. Thomasson wrote:
> On 9/2/2024 10:27 AM, jseigh wrote:
>> I read that arm added the cas instruction because they didn't think
>> ldxr/stxr would scale well.  It wasn't clear to me as to why that
>> would be the case.  I would think the memory lock mechanism would
>> have really low overhead vs cas having to do an interlocked load
>> and store.  Unless maybe the memory lock size might be large
>> enough to cause false sharing issues.  Any ideas?
> 
> Reservation granularity? Wrt the PPC, wow this an older thread:
> 
> https://groups.google.com/g/comp.arch/c/yREvvvKvr6k/m/nRZ5tpLwDNQJ
> 
> LL/SC can spuriously fail... It's more obstruction free than lock-free? 
> I think this is why a strong and weak CAS are in the C/C++ std's?
> 

Btw, have you talked with Alexander Terekhov lately? He is a smart guy. :^)