mem: Do not alter cache block state on uncacheable snoops

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

Changeset 11281:84339ca32391
---------------------------
mem: Do not alter cache block state on uncacheable snoops

This patch ensures we do not respond with a Modified (dirty and
writable) line if the request is uncacheable, and that the cache
responding retains the line without modifying the state (even if
responding).

Testing Done

Description:

~		Changeset 11263:8270998ad9b4
	~	Changeset 11281:84339ca32391

		mem: Do not alter cache block state on uncacheable snoops

		This patch ensures we do not respond with a Modified (dirty and
		writable) line if the request is uncacheable, and that the cache
		responding retains the line without modifying the state (even if
		responding).

Diff:

Revision 2 (+22 -7)

Show changes

src/mem/cache/cache.cc

src/mem/cache/cache.cc (Diff revision 2)

could we (at least theoretically) have an uncached write that invalidates cached copies as a side effect?

Andreas Hansson Dec. 24, 2015, 1 a.m. (Dec. 24, 2015, 1 a.m.)

We will eventually need to handle this case. At the moment I'd prefer to know when it happens, hence the panic.

For a whole-line write it's "easy", but for partial-line writes we need the CoherentXBar to help out and force writebacks (or do some pretty horrible in-place update). Patches are on the way.

Steve Reinhardt Dec. 24, 2015, 1:31 p.m. (Dec. 24, 2015, 1:31 p.m.)

OK... the comment could be expanded to reflect some of this discussion, but if it's a temporary situation, that's not necessary.

Ship It!

You have a pending review.

Review Board 2.0.15

This change has been marked as submitted.

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Description:

Changeset 11263:8270998ad9b4

Changeset 11281:84339ca32391

Diff:

Status: Closed (submitted)