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From: Terje Mathisen <terje.mathisen@tmsw.no>
Newsgroups: comp.arch
Subject: Re: Arm ldaxr / stxr loop question
Date: Thu, 14 Nov 2024 10:41:14 +0100
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aph@littlepinkcloud.invalid wrote:
> Terje Mathisen <terje.mathisen@tmsw.no> wrote:
>> aph@littlepinkcloud.invalid wrote:
>>> Chris M. Thomasson <chris.m.thomasson.1@gmail.com> wrote:
> 
>>>
>>> That's right, but my point about LDAR on AArch64 is that you can get
>>> sequential consistency without needing a StoreLoad. LDAR can peek
>>> inside the store buffer and, much of the time, determine that it isn't
>>> necessary to do a flush. I don't know if Arm were the first to do
>>> this, but I don't recall seeing it before. It is a brilliant idea.
>>
>> Isn't this just reusing the normal forwarding network?
>>
>> If not found, you do as usual and start a regular load operation, but
>> now you also know that you can skip the flushing of the same?
> 
> Yes. As long as the data in the store buffer doesn't overlap with what
> you're about to write, you can ship the flushing.
> 
>> PS. I do agree that it is a good idea (even patent-worthy?), but not
>> brilliant since it is so very obvious in hindsight.
> 
> LOL!  :-)
> 
>>
>> To me brilliant is something that still isn't obvious after larning
>> about it.
> 
> You have very high standards.

That is one of the reasons I never started a PhD track, I could never 
find an area of study that I thought would be sufficiently ground-breaking.

The other reason is/was that my friend Andy "Crazy" Glew did try the PhD 
route for several years and hit the same stumbling block vs his 
advisors, and I know that Andy is an idea machine well beyond myself.

Terje

-- 
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"