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I have a question about speculative execution and pipelining in CPUs, and I'm wondering: should I ask it on Stack Overflow? Or is it a software-only site?

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WHAT IS THE QUESTION THAT YOU WANT TO ASK? – jcolebrand Mar 2 '11 at 21:34
It's about how the CPU decides whether speculatively executing an instruction will have an unintended side effect (like a branch misprediction resulting in disk I/O). – Mehrdad Mar 2 '11 at 21:37
@drachenstern does it really matter though? I find the question interesting enough as it is, in order to see where it belongs – Pëkka Mar 2 '11 at 21:37
@drachenstern... it's okay, man. – Pops Mar 2 '11 at 21:37
@Pekka: Well if it's a software-only site then if I post it, it'll just get closed as "off-topic". :\ – Mehrdad Mar 2 '11 at 21:38
@Pekka ~ The original question as posed is highly entertaining, and generally encourages me to give a large consideration to the matter at hand. I'm genuinely ready to offer a stance to the asker merely on the merits of the original post. – jcolebrand Mar 2 '11 at 21:38
Please follow and submit good examples of such questions to… so the Computer Architecture and Organization stackexchange can move forward. – Adam Davis Mar 2 '11 at 21:55
@Polyanna: Oh, good idea! – Mehrdad Mar 2 '11 at 22:16
One of the mods should probably edit me and Adam's @eds so that they look correct :p Polyanna and drachenstern indeed! ;-) – jcolebrand May 14 '12 at 15:04
up vote 5 down vote accepted

I would like for Stack Overflow to accept such a question, and it has fielded processor-specific question in the past.

However you would have to very clearly write the question so that it appears to be a problem a regular programmer might run into, and that it's something they can solve via changing their code.

If you can't change the behavior of the problem, or solve it with a code change, then it doesn't belong on Stack Overflow.

So if you are asking theoretical questions about computer architecture then it probably doesn't apply, and the best bet is probably the Computer Science Stack Exchange, although that still might be a poor fit.

If you are asking people to enumerate all the ways that the current line of processors deal with such issues, then you probably should go to Super User.

But if you have a piece of assembly code that demonstrates the problem, and are asking for a solution, or if you notice a performance problem and you have a suspicion, and code that demonstrates the problem, then you should be safe on Stack Overflow.

However: there are very few people on Stack Overflow who would be able to answer your question with regards to all of today's most common processors.

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Look here Adam, that weren't his Q and you know it :p ~ However, I like where you've gone with this. Now that you've gone and generalized it, it starts to seem like a dupe of many other questions. – jcolebrand Mar 2 '11 at 21:55
Can we continue to generalize this and make up a "where do I put my question" sort of wizard app? Hmm, you spin the wheels in my brain. – jcolebrand Mar 2 '11 at 21:56
@drach - I tried to help people with this list of alternate places, but haven't kept it up to date (though others have to some degree). I don't know that this could be automated, but it would be nice if we could draw a nice chart for everyone, perhaps one part venn diagram and one part flowchart, that would help people better understand the differences between each site, the types of questions that should be acceptable, and where the gaps exist. – Adam Davis Mar 2 '11 at 22:00
Have you ever played with one of those 20Q games? you really should. – jcolebrand Mar 2 '11 at 22:01
@drach - Have you ever made one of those 20Q games? You really should. No, really, go ahead and start the database for the stackexchange twenty questions. We'll wait here. – Adam Davis Mar 2 '11 at 22:12
I figure there's 43 sites, how hard can it be? Oh, 44 sites. Look, it's only 45 sites. I'll uh ... brb. – jcolebrand Mar 2 '11 at 22:14
@jcolebrand It's been a year. Any progress? – Adam Davis May 16 '12 at 1:44
No Polyanna, I .. got busy .. – jcolebrand May 16 '12 at 14:52

First impression: hardware question → Super User.

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Exactly why I asked. Now what about your second impression? Is it the same or is it different? :) – Mehrdad Mar 2 '11 at 21:39
Beat me to it. I can't upvote because I reached my vote limit for the day but +1 – BinaryMisfit Mar 2 '11 at 21:40
I don't see this as a "user" question. – dmckee Mar 2 '11 at 22:48
@Diago what about today? :p – jcolebrand May 14 '12 at 15:00

I was just informed there is a site at

I would suggest starting there.

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Holy cow... didn't see that one coming o___o – Mehrdad Mar 2 '11 at 21:54
Oh hey, I didn't know that beta had started. +1 – Pops Mar 2 '11 at 22:00
The userbase there might be able to address it, but probably not. – Adam Davis Mar 2 '11 at 22:01
No, but they might be more into speculative pipelines and order of executions. I mean, chips aint code, even if there is some overlap – jcolebrand Mar 2 '11 at 22:05
@Pop, beta started in September or so. – mmyers Mar 2 '11 at 22:08
That should tell you something about how much I like electrical engineering, @mmyers. – Pops Mar 2 '11 at 22:38
Electrical Engineering definitely has users who can answer questions about pipelines and orders of execution. However, I think it's safe to assume that this guy is interested in x86, where we'll have more expertise in 8-bit processors, smaller ARM chips, and embedded processors on FPGAs. – Kevin Vermeer May 14 '12 at 14:36
@KevinVermeer It's about how the CPU decides whether speculatively executing an instruction will have an unintended side effect (like a branch misprediction resulting in disk I/O). – jcolebrand May 14 '12 at 15:02
Disk I/O? What's this 'disk' you speak of? :) – Kevin Vermeer May 14 '12 at 15:08
I happen to have quoted the OP's comment from directly below the Q – jcolebrand May 14 '12 at 15:08

This question can be answered by someone who knows processor architectures very well. Ideally a processor designer, but that's a very rare breed. It could also be a one of the few researchers in processor modelization (most likely to hang out on Theoretical Computer Science, though I haven't seen any), but that site only accepts research-level questions anyway. The largest target audience is compiler writers, and they're more likely to hang out on Stack Overflow. On this basis, I recommend Stack Overflow.

(And not Super User, which is for people who take processors and put them into computers, which is not your problem at all. SU would be appropriate for a question such as which CPU models have what features.)

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