Port: Stricter port bind/unbind semantics

Information
Submitter:	Andreas Hansson
Repository:	gem5
Branch:	default
Bugs:
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Description

Changeset 9157:e5872950c9a3
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Port: Stricter port bind/unbind semantics

This patch tightens up the semantics around port binding and checks
that the ports that are being bound are currently not connected, and
similarly connected before unbind is called.

The patch consequently also changes the order of the unbind and bind
for the switching of CPUs to ensure that the rules are adhered
to. Previously the ports would be "over-written" without any check.

There are no changes in behaviour due to this patch, and the only
place where the unbind functionality is used is in the CPU.

Testing Done

Ran a simple se and fs simulation and created and restored from
checkpoints for both.

Issue Summary

Description	From	Last Updated	Status
Actually, thinking about this, is this necessary? If I want to have the two sets of CPUs have their own ...	Tony Gutierrez	Aug. 23, 2012, 7:32 a.m.	Dropped

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src/cpu/base.cc (Diff revision 1)

Actually, thinking about this, is this necessary? If I want to have the two sets of CPUs have their own caches/TLBs and maintain their connections even when switched out, this assert will fail. Whereas with the check for a connection, this code will assume the new CPU already has a cache, or something connected to it, and function properly.

I guess it depends on what we want this functionality to do, if it's strictly for fast-forwarding then this is probably correct.

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Andreas Hansson Aug. 23, 2012, 5:37 a.m. (Aug. 23, 2012, 5:37 a.m.)

Well, if we want to support the case you mention, i.e. a flexible definition of what is switched and what is not, core, TLB, caches etc, then there are a lot of changes to do. Currently, what we switch is the core, and the code merely ensures that when a port is disconnected, then both parties agree and you only connect a port that is currently not connected. Makes sense?

I agree that it would be interesting to consider the notion of a core, CPU, cluster etc with different notions of what is switched, but that is a whole range of issues we have to sort out before we get there.

Tony Gutierrez Aug. 23, 2012, 6:23 a.m. (Aug. 23, 2012, 6:23 a.m.)
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agreed
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Issue Summary

Status: Closed (submitted)