ruby: remove wire buffer

Information
Submitter:	Nilay Vaish
Repository:	gem5
Branch:	default
Bugs:
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Description

Changeset 10881:4962564c4ce6
---------------------------
ruby: remove wire buffer

The structure is not being used anywhere.

Testing Done

... assuming no one chimes in to say they're using it in their own code.

I'd like to see Brad's comment on this. I know he pushed hard for this functionality a few years ago.

If I remember correctly, the purpose of the WireBuffer was to allow complicated inter-hardware communication without an explosion of state spaces. For instance, a probe filter co-located with the L3 cache. When you have these two structures implemented a single state machine you have a multiplicative effect on the number of states. But the WireBuffer would (theoretically) allow you to separate these two tightly-integrated structures into two different files.

Personally, I don't have any protocols that use the WireBuffers. However, I have often suggested to others that they use WireBuffers.

yYes, we use the wire buffer in our protocols and oppose its removal. (What's the opposite of the "Ship It" button?) Brad is on vacation today so I'll comment on his behalf :).

Brad Beckmann June 22, 2015, 10:51 a.m. (June 22, 2015, 10:51 a.m.)

Nilay please when commenting on a patch, use Reviewboard rather than directly replying to an email. It is very hard to keep track of your comments over email.

On 6/19 Nilay said "Steve, can you spell out the difference between the WireBuffer and the MessageBuffer classes?"

The wire buffer is not a virtual channel buffer, rather it mimics an actual wired communication between to controllers. As Jason points oout, it allows us to closely tie controllers together and take advantage of ordering properties not provided by MessageBuffers.

Nilay Vaish June 23, 2015, 1:40 p.m. (June 23, 2015, 1:40 p.m.)

You write what you think the WireBuffer is doing. Have you read the code? How do you make sense of a data structure that has queue-like semantics for inserts and heap-like for deletes and recycles? What
wire behaves in this fashion? Or for that matter what wire has buffering associated with it?

Nilay Vaish June 23, 2015, 2:40 p.m. (June 23, 2015, 2:40 p.m.)

One more thing that you may not be aware of. You can connect two controllers
directly using message buffers without going through the network. So, you
probably do not require WireBuffer anyway.

Nilay Vaish June 25, 2015, 9:52 a.m. (June 25, 2015, 9:52 a.m.)

Is AMD further interested in arguing about this data structure?
I am completely confident whatever Brad claimed is not what this
data structure does. And MessageBuffer with ordered=true would
serve the purpose as long as two controllers are directly connnected.
Unless anyone speaks on this issue soon enough (end of next week or so),
I am going assume this debate has concluded and commit this patch.

Steve Reinhardt June 25, 2015, 11:43 a.m. (June 25, 2015, 11:43 a.m.)

We are not interested in further argument. We are using this structure and it should not be removed. We believe that should be sufficient argument for not committing this patch.

You have a pending review.

Review Board 2.0.15

This change has been discarded.

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Status: Discarded