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NNTP-Posting-Date: Wed, 13 Nov 2024 18:13:04 +0000
Sender: Andrew Haley <aph@zarquon.pink>
From: aph@littlepinkcloud.invalid
Subject: Re: Arm ldaxr / stxr loop question
Newsgroups: comp.arch
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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.

Andrew.