Re: Arm ldaxr / stxr loop question

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"